CN101283507B

CN101283507B - Methods and systems for protecting charge transfer capacitance sensor for proximity detection

Info

Publication number: CN101283507B
Application number: CN2006800194937A
Authority: CN
Inventors: J·K·雷诺
Original assignee: Synaptics Inc
Current assignee: Synaptics Inc
Priority date: 2005-06-03
Filing date: 2006-06-03
Publication date: 2011-03-30
Anticipated expiration: 2026-06-03
Also published as: CN101213461A; CN101283507A; CN101213461B; CN101273274A

Abstract

Methods, systems and devices are described for determining a measurable capacitance for proximity detection in a sensor having a plurality of sensing electrodes and at least one guarding electrode. A charge transfer process is executed for at least two executions. The charge transfer process includes applying a pre-determined voltage to at least one of the plurality of sensing electrodes using a first switch, applying a first guard voltage to the at least one guarding electrode using a second switch, sharing charge between the at least one of the plurality of sensing electrodes and a filter capacitance, and applying a second guard voltage different from the first guard voltage to the at least one guarding electrode.; A voltage is measured on the filter capacitance for a number of measurements equal to at least one to produce at least one result to determine the measurable capacitance for proximity detection.

Description

Protection is used for the method and system of the charge transfer capacitance transducer of proximity detection

Priority data

The application requires in the U.S. Provisional Patent Application sequence number 60/687 of submission on June 3rd, 2005,012,60/687,166,60/687,148,60/687,167, the sequence number of submitting on February 16th, 60/687,039 and 60/687,037 and 2,006 60/774,843 priority, and at this with their introducings for your guidance.

Technical field

The present invention relates generally to capacitance sensing, and relate to more especially and utilize the charge transfer technology of conversion can detect device, the system and method that to measure electric capacity.

Background technology

Capacitance sensor/the sensing system of response electric charge, curtage can be used for detection position or proximity (or motion or existence or some similar information), and generally is used as the input unit of computer, PDA(Personal Digital Assistant), media player and register, video game computer, consumer-elcetronics devices, cell phone, coin telephone, point of sales terminal, ATM, phonebooth etc.The capacitance sensing technology is used in the application of the input of for example user's load button, Sliding Control, rolling ring, rolling band and other type and control.Employed one type capacitance sensor is the button-type transducer in this application, and it can be used to provide the information about input proximity or existence.The capacitance sensor of employed another type is a touchpad sensor in this application, and it can be used to provide the information about input, for example position, motion; And/or along an axle (1-D transducer), two axles (2-D transducer) or the similar information of multiaxis more.Button-type transducer and touchpad sensor can also randomly be configured to the information that provides other, for example some indications of the power that is associated with input, duration or capacitive coupling amount.License at people's such as Trent U.S. published application 2004/0252109A1 with on March 9th, 1999 based on the example of the 1-D of capacitance sensing technology and 2-D touchpad sensor in people's such as Gillespie the U.S. Patent number 5,880,411 and describe to some extent.For example, in the input unit of the electronic system that comprises handheld computer and notebook computer, find this 1-D and 2-D transducer easily.

The user generally comes the operation of capacitor input unit by place or move one or more finger pieces, contact pilotage and/or object at the sensing region that is arranged in the one or more transducers on the input unit or among the input unit near input unit.In case carrier signal be applied to can be detected sensing region relevant with positional information (for example (or a plurality of) position, proximity, one (or a plurality of) motion and/or a similar information) about sensing region and excitation/stimulation, this will produce capacity effect.This positional information can be used to again to select, moves, the combination in any of text, figure, pointer, highlighted part and/or any other indicating device on rolling or the operating display.This positional information can also be used for making user and interface to interact, and for example controls volume, regulates brightness or realizes any other purpose.

Although extensively adopted capacitance sensor, the sensor designer still continues to seek the mode of the functional and usefulness that improves transducer.Especially, the engineer continues to strive for reducing the influence of parasitic noise to this transducer.For example, the current shielding sensing region that all comprises of many capacitance sensors makes it not to be subjected to ground level or other structure of external noise signal and internal noise effect of signals.Though the ground level that keeps on rough constant voltage and the shielding of other type can prevent some parasitic noise disturb sensor operations effectively, they also can for example reduce sensor resolution or increase ghost effect by increasing parasitic capacitance.Therefore, the performance of this device is desirable anything but.

Therefore, be desirable to provide and be used for apace, detect effectively and efficiently and can measure the system and method that electric capacity prevents by spurious noise signal simultaneously and/or strengthens at least some adverse effects that resolution produces.And, wish to create for example scheme implemented of standard ℃, microcontroller and passive component of a kind of parts that can utilize easy acquisition.In conjunction with the accompanying drawings with aforesaid technical field and background technology, from subsequently detailed description and appended claim, the feature of other hope and characteristic will be conspicuous.

Summary of the invention

Describe such mthods, systems and devices, be used for being identified for the electric capacity measured that proximity detects at transducer with a plurality of sensing electrodes and at least one guard electrode (guarding electrode).The electric charge transfer processing carries out at least twice.The electric charge transfer processing comprises utilizes first switch that predetermined voltage is applied in a plurality of sensing electrodes at least one; utilize second switch that the first protection voltage is applied at least one guard electrode; be shared in the electric charge between at least one and the filter capacitor in a plurality of sensing electrodes, and the second protection voltage that will be different from the first protection voltage is applied at least one guard electrode.Measuring voltage on filter capacitor is measured number and is equaled at least once, thereby is identified for the electric capacity measured that proximity detects to produce at least one result.

Utilize technology described herein; protection capacitance detecting scheme can utilize the parts of easy acquisition to implement expediently, but and sensing implement button, slide block, cursor control or user interface navigation feature appoint the finger piece, contact pilotage of other function or the position of other object relevant with capacitance sensor aspect be particularly useful.

Description of drawings

To describe various aspects of the present invention in conjunction with the following drawings hereinafter, wherein identical Reference numeral is represented components identical, and:

Figure 1A is used to utilize the conversion charge transfer technology with protection to detect the flow chart of the exemplary technique of electric capacity;

Figure 1B is the calcspar that comprises the exemplary electrical capacitance proximity sensor of protective circuit;

Fig. 1 C is the timing diagram about the exemplary technique that is used to operate the electrical capacitance proximity sensor with Figure 1B protective circuit;

Fig. 2 A-B is the timing diagram that is applied to the exemplary guard signal of guard electrode.

Fig. 3 A-E is the calcspar of demonstrative circuit that is used to produce the protection voltage of guard signal;

Fig. 4 A-E is the more detailed block diagram of demonstrative circuit that is used to produce the protection voltage of guard signal; With

Fig. 5 is the proximity transducer schematic representation of apparatus with electronic system.

Embodiment

Below detailed description only is exemplary in essence and is not meant restriction the present invention or application of the present invention and use.In addition, be not meant by any expression that proposes in aforesaid technical field, background, summary of the invention or the following detailed description or theoretical hint and limited.

According to various one exemplary embodiment, utilize the easy design capacitance of two or more switches to detect and/or measuring circuit.And the guard signal with two or more protection voltages can utilize one or more other switches and one or more passive electronic network (it can be simple lead or complicated network) to be applied to guard electrode; This can be used for shield sensor makes it not carry out undesirable electric coupling, improves sensor performance thus.In typical enforcement, carry out that the electric charge transfer processing repeats twice or repeatedly.In the electric charge transfer processing; utilize one or more switches that predetermined voltage is applied to and to measure electric capacity; and with second switch the first protection voltage is applied to guard electrode, in passive network, can measures electric capacity and filter capacitor and share electric charge and the second protection voltage is applied to guard electrode.Utilize this electric charge transfer processing, repeatedly apply predetermined voltage and share the voltage that can influence on the filter capacitor with relevant electric charge.Voltage on the filter capacitor can be the voltage at circuit node place of the voltage at expression filter capacitor two ends.Voltage on the filter capacitor also can be the voltage at the two ends of filter capacitor own.The electric charge transfer processing can think thus in repeatedly carrying out with electric charge roughly " combination " to filter capacitor so that " output " voltage of filtration filter capacitor.The electric charge transfer processing can only be utilized switch and passive component, and for example resistance, electric capacity and/or inductance carry out.After repeating electric charge transfer processing one or many, measure the voltage (electric charge on its expression filter capacitor) on the filter capacitor.One or more measurements can be used to produce one or more results and determine can measure electric capacity.The measurement of voltage can be simple as the voltage on the filter capacitor is compared with threshold voltage on the filter capacitor, or as extract the rapid analog-to-digital conversion complexity of electric charge and measuring voltage multistep repeatedly from filter capacitor.Utilize these technology, can easily design the existence that can detect finger piece, contact pilotage or other object or the capacitive position sensor of proximity.In addition; each embodiment of protection described herein (for example only utilizes conventional switching mechanism; the signal pin of control device) and passive component (for example; one or more capacitors, resistance, inductance etc.) implement easily, and do not need to increase the extra active electronic device of cost and complexity.Various resist technology described herein can use with electric charge and shift similar parts of detection technology and method.With the integrated simple coupling of multichannel, the protection that this provides high efficiency to implement.As a result, the parts that utilize obtainable easily and appropriate price still can be under various environment facility implement various protection scheme described herein (with sensing scheme if desired) reliably, describe more comprehensively as following.

With reference now to Figure 1A,, show and be used to detect the exemplary technique 800 that can measure electric capacity, it provides protection can measure electric capacity with shielding and makes it not carry out undesirable electric coupling.This method 800 uses the electric charge of conversion to shift to detect can measure electric capacity, and especially may be used on being used for the detection of the electric capacity that object space detects.This technology suitably comprises following wide in range step: carry out electric charge transfer processing (step 801) twice or repeatedly (as repeating by step 810) and optionally measure voltage on the filter capacitor with bear results (step 824) with voltage protection.Electric charge transfer processing 801 comprises predetermined voltage is applied to can measure (step 802) on the electric capacity.Then, the first protection voltage is applied to (step 804) on the guard electrode.Be applied at predetermined voltage and can measure before electric capacity stops, the first protection voltage preferably is provided.Then, share electric charge (step 806) by measuring electric capacity and filter capacitor." sharing " electric charge in this context has referred to the seedbed conversion can measure electric capacity and filter capacitor with coupling, there is the seedbed to be transformed into another place in the system, the transfer of guiding electric charge in other mode, or do not have the seedbed by static or other inertia and make electric charge shift impedance.Then, the second protection voltage is applied to guard electrode (step 808).The second protection voltage is different from the first protection voltage, and preferably is applied to guard electrode before electric charge is shared basic the end.The electric charge transfer processing repeats at least once (step 810) at least two kinds of performances in the electric charge transfer processing sum, and can repeat many times.Can repeat the voltage of electric charge transfer processing on filter capacitor and surpass threshold voltage, until and/or according to arbitrary other scheme, handle 801 and carry out pre-determined numbers.When the electric charge transfer processing is carried out, provide the first and second protection voltages to shield undesirable electric coupling.

The voltage of measuring on the filter capacitor can occur in any time with bear results (step 824), be included in before the electric charge transfer processing, afterwards and during.In addition, the each repetition can not measured the voltage 824 on the filter capacitor, can measure voltage 824 one or many on the filter capacitor so that the electric charge transfer processing number of measurement result number and execution can be any ratio, comprise one than many, one to one and compare one more.When the voltage substantially constant on the filter capacitor, preferably measure the voltage on the filter capacitor.When determining to measure the value of electric capacity, use one or more measurement results.Can obtain to measure the value of electric capacity according to any technology.In each embodiment, carry out this based on the value (for example, filter capacitor) of known elements in the measurement of the voltage on the filter capacitor (electric charge of its expression on filter capacitor), the system and number of times that electric charge transfer processing 801 is performed and determine.As just mentioning preceding, carry out handle 801 concrete number of times can be according to predetermined value, determine according to the voltage at the filter capacitor two ends that intersect with threshold voltage or as suitable any other factor.

Repeating step 802-808 and step 824 (step 810) as required.For example, in proximity transducer is implemented, determine repeatedly corresponding to the general per second of the electric capacity measured of each sensing electrode.This provide near the proximity of object definite transducer and proximity change ability and be convenient in the device of user's input, use this processing thus.Thus, can repeat this processing with the high speed of per second, can realize that per second carries out measuring many times determining of electric capacity for each sensing electrode.

Can carry out in any way and handle 800.In each embodiment, software by being present in digital storage (for example being positioned at memory controller or that communicate by letter with controller) or any other digital storage media (for example, CD or disk, be transmitted in modulation signal on the carrier wave etc.) or firmware are carried out and are handled 800.The processing of as above discussing 800 and its each equivalent and derivative also can be carried out with programmed circuit or other logic of suitable any type.

The step that applies the first and second protection voltages can be implemented with various technology and device.For example; (for example can utilize switching mechanism and passive component; one or more capacitors, resistance, inductance etc.) protection voltage is provided, and do not need to increase the extra active electronic device (can be used for providing appropriate protection voltage) of cost and complexity with Low ESR although comprise DAC and the such active electronic device of follower.

Present initial reference Figure 1B, exemplary capacitance sensor 100 suitably comprises three sensing electrode 112A-C and a guard electrode 106.Sensing electrode 112A-C is directly coupled to switch 116-C respectively.Sensing electrode 112-C also passes through direct and filter capacitor (" integrated capacitance " or " integrated filter ") 110 (C of passive impedance 108A-C respectively _F) coupling.Also show filter capacitor 110 and be directly coupled to switch 118.Guard electrode 106 is coupled to the protection voltage generation circuit 104 that comprises passive protection net 105 and one or more switch 114.Protection voltage generation circuit 104 provides suitable guard signal (V _G) 103.And shown in Figure 1B, be stimulus 101, it is not the part of capacitance sensor 100 and is detected by capacitance sensor 100.Although Figure 1B shows a contact pilotage, stimulus 101 can be one or more finger pieces, contact pilotage, object etc.

Although Figure 1B shows the concrete configuration of transducer 100, it should be understood that to have many other configurations.Other embodiment of capacitance sensor 100 can comprise sensing electrode, guard electrode, filter capacitor, passive impedance, switch, protection voltage generation circuit and the controller for the suitable any amount of transducer.They can also be any ratios that is suitable for transducer; For example, as allow by the sensing scheme of using many than one, one than many, one to one or how to put than polygamy, sensing electrode also can be coupled to the filter capacitor that has or do not have passive impedance.It should be noted that, though Figure 1B shows switch 114,116A-C and 118 that all I/O that utilize controller 102 implement, but this only is an exemplary embodiment, and these and other switch can be implemented with the various different devices that comprise the discrete switch that is different from any controller.As other example; transducer can use the passive protection net that is made of single wire or more complicated circuit network; perhaps transducer also can utilize single switch or a plurality of switch (it can comprise the one or more I/O that utilize controller, multiplexer, digital to analog converter (DAC) etc., because each multiplexer or DAC comprise a plurality of switches) that guard signal is provided.Can use switch so that guard signal to be provided with multiple mode, comprise off switch, open switch or start it in some other mode (for example, PWM and pulse code modulation).Therefore, can apply voltage by off switch and by opening switch, this depends on how circuit is arranged.Also can use other analog component (for example, in order to cushion the output of passive protection net 105).

Sensing electrode 112A-C provides and can measure electric capacity, the variation of the electric field that its value representation and stimulus 101 are relevant.Each can measure the effective capacitance of electric capacity representative by capacitance sensor 100 detectable associated sensed electrode 112A-C.In " absolute capacitance " detection scheme, can measure total effective capacitance of the local ground connection of electric capacity representative from the sensing electrode to the system.In " shift electric capacity (trans-capacitance) " detection scheme, can measure electric capacity and represent total effective capacitance between sensing electrode and the one or more drive electrode.Thus, total effective capacitance can be quite complicated, relates to as series connection and electric capacity, resistance and inductance in parallel by sensor design and operational environment definition.Yet, in many cases, can simple analog from the electric capacity measured of input as and fixing background capacitance little variation electric capacity in parallel.

In order to determine to measure electric capacity, utilize the switch 114 of any amount, 116A-C that suitable voltage signal is imposed on each electrode 106,112A-C.In each embodiment, the operation of switch 114,116A-C is by controller 102 (it can be microprocessor or other controller arbitrarily) control.By utilizing switch 116A-C to apply appropriate signal, can determine the electric capacity measured that shows by electrode 112A-C (difference).And; by utilizing switch 114 to apply appropriate signal; can produce suitable protection voltage and be placed on guard signal 103 on the guard electrode 106, can measure the influence that electric capacity makes it not to be subjected to undesirable noise and other parasitic signal with duration of work shielding at transducer 100 with generation.

Guard electrode 106 is to show the arbitrary structures of the protection voltage that comprises guard signal 103 that applies, to prevent and one or more undesirable capacitive coupling of measuring electric capacity.Although Figure 1B shows the guard electrode 106 with " pectination " profile; but show this profile for convenience of explanation; and as can be applicable among the equivalent embodiment of any amount of design of transducer 100, guard electrode 106 can be any other form or shape.For example, sensing electrode 112A-C can or have some other shapes with some other patterned arrangement, and the shape of guard electrode 106 can be arranged suitably.Guard electrode 106 can also wiring around all or part of periphery of one group of sensing electrode, so that small part shields the influence that this group is not subjected to environment.Guard electrode 106 can not be subjected to the influence of any electronic device of sensing electrode back to shield them in the wiring of at least a portion sensing electrode back.Guard electrode 106 can also connect up between sensing electrode and not be subjected to each other influence to shield them.Guard electrode does not need to extend in the total length between the sensing electrode or covers whole sensing electrodes to provide the protection with level.For example, the part that guard electrode 106 can only parallel sensing electrode 112A-C, or insert some or all of sensing electrode 112A-C.In addition; if use " transfer electric capacity " detection scheme; then guard electrode 106 can connect up around arbitrary region; guard electrode 106 can be disturbed sensing electrode 112A-C and the capacitive coupling between the drive electrode, for example some zones between sensing electrode 112A-C and the drive electrode arbitrarily in this zone.As described below, guard electrode 106 and the capacitive coupling that can measure between the electric capacity can be via switch 114 by applying suitable protection voltage control.

In the one exemplary embodiment shown in Figure 1B, provide filter capacitor 110 by one or more capacitors (for example discrete capacitor of any amount), to receive the electric charge that shifts from sensing electrode 112A-C.Although selected concrete filter capacitor value will change to another embodiment from an embodiment, the electric capacity of each filter capacitor 110 is generally bigger, perhaps than the electric capacity that can measure electric capacity one or two order of magnitude greatly only, but often big several magnitude.For example, when the desired value that can measure electric capacity was several pico farad orders of magnitude etc., filter capacitor 110 can be designed to several millimicrofarad orders of magnitude.Yet the actual value of filter capacitor 110 can change, and this depends on certain embodiments.

Although particular instance has been shown in Figure 1B, the principle of the capacitance sensing that combines with protection can be applied to the two ends of the sensor construction 100 of wide array.In the one exemplary embodiment shown in Figure 1B, each sensing electrode 112A-C with each relevant electric capacity measured thus, is coupled to shared filter capacitor 110 by relevant passive impedance 108A-C.Under suitable situation, can measure electric capacity for each, optional embodiment can use a plurality of filter capacitors and/or passive impedance.Optional embodiment also can share a plurality of passive impedance and/or filter capacitors of measuring between the electric capacity.When comprising passive impedance 108A-C, generally for example the diode, capacitor, inductance, resistance etc. of any type provide passive impedance 108A-C by one or more non-active electronic components.Usually each passive impedance 108A-C of design has enough big impedance to prevent between the electric capacity charge period that a large amount of electric currents from flowing into filter capacitors 110 can measuring, as following description more comprehensively.In each embodiment, impedance 108A-C can be 100 kilohms or the more order of magnitude, although other embodiment can utilize very different resistance values.Yet once more, passive impedance 108A-C does not need to be present in and otherwise implements among all embodiment that electric charge shares.

The operation of transducer 100 suitably comprises the electric charge transfer processing and is handled by the measurement of using one or more switch 116A-C, 118 to be easy to realize, utilizes switch 114 to apply guard signal 103 simultaneously.Once more, implement switch 114,116A-C and/or 118 although show the I/O that utilizes controller 102, but switch 114,116A-C and/or 118 can implement with discrete switch, multiplexer, field-effect transistor and/or other construction of switch of any type, only propose several examples at this.Alternatively, some switches 114,116A-C, 118 can implement with the internal logic/circuit of output pin that is coupled to controller 102 or I/O (I/O) pin, shown in Figure 1B.If you are using, this I/O pin can also provide input function and/or other switch.For example, switch 118 can be implemented with the I/O 119 that is also connected to or comprise the input capability in the controller 102.This input capability can be used for measuring directly or indirectly the voltage on the filter capacitor 110, and comprises multiplexer, comparator, magnetic hysteresis threshold values, CMOS threshold value or analog to digital converter.Such I/O pin generally can switchably be used one or more logical values and/or " high impedance " or " open circuit " value by the internal switch that supply voltage is coupled in utilization.Logical value can be voltage or other signal of any appropriate.For example, logic " height " or " 1 " value are corresponding to " height " voltage (for example, 5 volts), and logic " low " or " 0 " value are corresponding to relative " low " voltage (for example, local system ground connection ,-5 volts etc.).The signal specific of selecting and applying can change to another embodiment significantly from an embodiment, and this depends on the sensing scheme of specific controller 102, sensor configuration and selection.For example, current source, pull-up resistor or digital to analog converter (DAC) also can make and be used to provide suitable voltage, and can be at controller 102 outside or inner.

The advantage of many embodiment is only to utilize passive component can implement very general capacitance sensor 100 easily in conjunction with controller 102, and controller 102 is conventional digitial controllers that the combination in any by one or more microcontrollers, digital signal processor, microprocessor, programmable logic array, integrated circuit, other control circuit etc. constitutes.Many these controller products are easily from comprising the Microchip Technologiesof Chandler of Arizona State; The Freescale Semiconductor ofAustin of Texas; Obtain with each commercial sources of the TexasInstruments of Richardson of Texas etc.Controller 102 can comprise digital storage (for example, static, dynamic or quickflashing random access memory), and it can be used to store the employed data of the various electric charge transfer processing of execution program and the instruction of the various capacitance sensors that are used for comprising here.In each embodiment operating period, need comprise the operation of switch 114,116A-C and 118 at the only electric excitation on the sensing electrode 112A-C electric capacity measured relevant that the operating period of transducer 100 takes place with them; But this operation respond packet is contained in configuration, software, firmware or other instruction in the controller 102 and takes place.

The electric charge transfer processing, its general repetition twice or more times, suitably comprise utilize first switch apply predetermined voltage (for example supply voltage, cell voltage, or logical signal) giving the applicable electric capacity charging of measuring, passive in appropriate circumstances then or have the seedbed to allow applicable electric capacity and the filter capacitor arbitrarily (for example 110) measured to share electric charge.Passive sharing can be shifted by for example resistance realization of impedance by electric charge, and active sharing can realize that this switch can be used to measure and be capacitively coupled to suitable filter capacitor by energizing switch.

The normally single suitable voltage of predetermined voltage, for example supply voltage, cell voltage, digital logic level, by any separation or amplification form etc. in the resistance of driven with current sources, these voltages.Scheduled voltage generally is known, and generally remains unchanged; Yet, all need not be this situation, as long as predetermined voltage keeps ratio scale (ratiometric) with the measuring voltage that can use on the filter capacitor (for example 110).For example, the capacitance sensing scheme can comprise the filter capacitor that resets to resetting voltage, and also comprises by the voltage on voltage (comparing resetting voltage) on comparison filter capacitor one side and threshold voltage (also than resetting voltage) the measurement filter capacitor.Utilize this sensing scheme, poor between predetermined voltage and the resetting voltage, and poor between threshold voltage and the resetting voltage should keep roughly being in ratio, carry out the electric charge transfer processing on average can cause determine to measure electric capacity.Thus since the term of execution being used for determining measuring the electric charge transfer processing of electric capacity from measuring the electric charge that electric capacity is shared to filter capacitor, will be proportional so be used to measure the threshold value of change in voltage on the filter capacitor with the change in voltage on the filter capacitor.Especially, be V at predetermined voltage _DdAnd resetting voltage is under the situation of GND, and threshold voltage can be a ratio scale for CMOS input threshold value, for example (1/2) * (V _Dd-GND).

Example shown in Figure 1B can be with as being worked by the mode shown in Fig. 1 C.In by the embodiment shown in Figure 1B-C, each switch 116A-C applies the predetermined voltage with " charging pulse " 201, the RC time constant of phase specific impedance 108A-C and filter capacitor 110, should generally have the short relatively cycle by " charging pulse " 201, and the relevant RC time constant of measuring electric capacity with it of phase specific impedance 108A-C preferably has the short relatively cycle.This makes the electric charge that adds filter capacitor 110 during the electric charge transfer processing to mainly actively measure on the electric capacity and electric charge that share with filter capacitor 110 from being stored in, and lessly comes leisure to apply during the predetermined voltage by the mobile electric current of associated impedances (for example 108A-C).This helps to prevent that too much electric current from revealing by impedance 108A-C.Shown in Fig. 1 C, before applying predetermined voltage, each charging pulse 201 provides the relative brief duration of " opposite " " discharge voltage " (voltage with amplitude opposite with predetermined voltage) in addition.Discharge voltage can compensate any electric current of revealing by impedance 108A-C during the electric charge transfer processing; The optional feature that needs among this not all embodiment.Can use not only voltage level in an execution or in the predetermined voltage between a plurality of execution, and this is suitable for also for opposite voltage.Yet predetermined voltage and opposite voltage (if you are using) have constant substantially voltage in many cases.

Below discuss to have described and to measure electric capacity (for example, 112A-C is relevant with sensing electrode), a filter capacitor 110 and a common passive impedance (for example, operation 108A-C) with a guard electrode (for example 106), one.This is for clarity, and it should be understood that, a plurality of electric capacity, passive impedance and filter capacitors measured can be included in the system, and they can be connected (at least partially or completely separating on the time) or (at least partially or completely overlapping on the time) in parallel work.

Predetermined voltage is applied to can measure electric capacity after, permission can be measured electric capacity and filter capacitor and be shared electric charge.Share electric charge in order to allow to measure electric capacity, make the passive transfer of electric charge without any need for operation except stopping to apply predetermined voltage and interrupting time enough.In each embodiment, can (for example lack relatively break period, if filter capacitor is directly connected to the electric capacity measured of connecting with small resistor), maybe can occur some time of delays (for example, electric charge shift by with can measure the bigger resistance that electric capacity, filter capacitor and reference voltage are connected).In other embodiments, allow the electric charge transfer to comprise and stop to apply predetermined voltage and have the seedbed one or more switches relevant of excitation can measure electric capacity and filter capacitor, and/or carry out other suitable operation with coupling with controller.For example, utilize " sigma-delta " technology can occur the electric charge of sharing with filter capacitor in other embodiments; For example at filter capacitor via measuring in electric capacity charging and the processing by the discharge of " delta " electric capacity (not shown), vice versa.As another example, the electric charge shared with filter capacitor can appear in the switch (not shown) that can measure electric capacity and filter capacitor or coupling and uncoupling filter capacitor and supply voltage by excitation coupling and uncoupling.In such embodiments, can there be for example impedance shown in the 108A-C shown in Figure 1B, can increases passive or active element, and/or as suitable replacing by passive or active element.

(for example wherein utilize one or more active parts, by the active switch that opens or closes) can occur measuring the electric charge transfer processing of sharing electric charge between electric capacity and the filter capacitor, clearly illustrate that with these excitations of active parts and share the beginning and the end in cycle.Equally, wherein by energizing switch to the Low ESR reference voltage, can measure the electric charge transfer processing that electric capacity is directly connected to filter capacitor one side and is coupled to the filter capacitor opposite side, also clearly illustrated that the beginning and the end in shared cycle.On the contrary, the electric charge transfer processing of passive shared electric charge has a not clear electric charge cycle of sharing and represents.In the system of passive shared electric charge, think that the electric charge cycle of sharing begins when applying the predetermined voltage termination; When the electric charge cycle of sharing must begin (carrying out the electric charge transfer processing subsequently) at charging pulse subsequently or before and when filter capacitor resets or before finish (if using the end that resets and show one group of electric charge transfer processing).The shared cycle can finish before the charging pulse subsequently and before any resetting, and voltage is enough similar to make insignificant electric charge stop effectively when shared can measuring between electric capacity and the filter capacitor because electric current is flowing in; This is can measure simultaneously the situation that electric capacity and filter capacitor intercouple through time enough.Yet even voltage is not equal substantially before subsequently charging pulse or reset signal, electric charge is shared still when charging pulse or reset signal begin and is finished.This is because be coupled to (for example in the transducer 100 at Figure 1B) in the passive shared system that can measure electric capacity at filter capacitor always, applies any electric charge that the influence of charging pulse or reset signal can measure between electric capacity and the filter capacitor and shares.Any electric charge that the low impedance path of charging pulse or reset signal refers on the electric capacity of sharing with filter capacitor measured can be ignored until removing low impedance source.

Can measure processing in the arbitrfary point of the electric charge transfer processing that is suitable for employed sensor configuration and sensing scheme, and the performance of performance number of measure handling and the electric charge transfer processing that is suitable for employed sensor configuration and sensing scheme can be any ratio.For example, measure to handle and to share electric charge between electric capacity and the filter capacitor and voltage on the filter capacitor is positioned at from some percentage point of asymptote after carry out can measuring, or measure processing and can when carrying out the electric charge transfer processing, carry out at every turn.On the contrary, when applying predetermined voltage, can measure processing (if filter capacitor prevents rightly at that time and can measure capacitance charge and share).Can only measure processing, or only after repeatedly repeating to take place, measure processing for one group of repeated electric charge transfer processing.The measurement of voltage can be as comparing the voltage on the filter capacitor simple (for example in " sigma-delta " scheme) on the filter capacitor with threshold voltage, or as the rapid analog-to-digital conversion of multistep complicated when the voltage on the filter capacitor is pronounced the multidigit value then (for example when the electric charge transfer processing of carrying out dose known amounts and).For example in other double slanted sensing system that the voltage on oscillator or the filter capacitor drives, and in the multi-bit ADC of the voltage on using many threshold measurements filter capacitor, also can use many threshold values between low and high threshold.Can carry out one or more measurements, and if suitable just storage, to determine the applicable electric capacity of measuring.

Can be in many pieces of documents, at U.S. Patent number 5,730,165,6,466,036 and 6,323, in 846 and on June 3rd, 2006 is in Methods and Systems for Detectinga Capacitance Using Switched Charge Transfer techniques and the U.S. Patent application of on June 3rd, 2006 by people's such as KirkHargreaves Methods and Systems for Detecting a Capacitance Using Sigma-DeltaMeasurement Techniques by the title of people such as David Ely application, finds the more details about specific capacitor sensing scheme.Have, specific in other embodiments capacitance sensing technology and sensor construction 100 can change significantly again.

Can be subjected to the influence of environment without any the system of shielding or protection.Therefore, as formerly described, many capacitance sensors comprise that ground level or shielding sensing region are not subjected to other structure of outside and internal noise effect of signals.Yet ground level is desirable anything but with the shielding that remains on other type under about constant voltage, and they can increase the effect of parasitic capacitance (or other spurious impedance and relevant charge leakage) and reduce resolution or dynamic range.On the contrary, the low-impedance protection of driving can provide similar shielding, and can significantly not increase the effect of parasitic capacitance or reduce resolution.This is to pass the electric charge that any parasitic capacitance relevant with any guard electrode transfer on any filter capacitor to carry out by minimizing during execution causes determining measuring the process of electric charge transfer processing of electric capacity.The voltage of protection can provide by the output of using the self charge transfer processing, and is similar with the voltage of protection.Can provide this output to have the input of the buffer (or other follower circuit) of low-impedance a plurality of sense channel as protection.Alternatively, these protection voltages can also directly provide by utilizing protection-electric charge transfer processing (for the processing of protecting purpose to carry out), and this protection-electric charge transfer processing provides low-impedance guard signal inherently so that do not need other buffering; This protection electric charge transfer processing can also be similar with the electric charge transfer processing that is used for the sensing use, but do not need.

General electric charge shift the sensing scheme carry out the electric charge transfer processing repeatedly (often be hundreds of time or more) be used for determining the measurement that can measure electric capacity with generation.This group electric charge transfer processing that causes being used for a definite measurement changes between embodiment.As four examples, this group can reset between attitude and the final threshold value attitude for the system that is charged to threshold value; This group can be in initial state and final reading between the attitude for carrying out one group of a plurality of electric charge transfer processing and reading the system of one or more multidigit voltages outputs; This group can be between low and high threshold for double inclined plane or oscilator system; This group can also be the sampling length of digital filter for sigma-delta system.This group electric charge transfer processing defines the group of considering total protective effect, or " process of carrying out the electric charge transfer processing can cause measuring determining of electric capacity ".

To transfer to net charge on the filter capacitor in order reducing during execution causes determining measuring the process of electric charge transfer processing of electric capacity, can to apply guard signal with due care voltage by the parasitic capacitance relevant with guard electrode.Predetermined charging voltage is applied to can be measured electric capacity and can continue some times, and before this continued to finish, the first protection voltage similar to this predetermined voltage can be applied to suitable guard electrode.Because predetermined voltage generally is very constant, so the first protection voltage generally can be single about constant voltage.Then, can measure share all electric charges between electric capacity and the relevant filter capacitor before (that is, and electric charge share finish before), the guard signal that is applied to guard electrode can change to correlation filtering electric capacity on the similar second protection voltage of voltage.Have again, although in this argumentation, used odd number, can comprise any amount guard electrode, can measure electric capacity, impedance, filter capacitor etc.

In the embodiment shown in Figure 1B, guard electrode 106 is provided above low impedance path, forming the protection voltage of guard signal 103 during the sense process at least roughly near the voltage on the active electrode (for example 112A-C).Charge and to measure electric capacity if apply quite constant predetermined voltage, then can comprise the single voltage similar finishing the guard signal 103 that is applied to guard electrode 106 before applying predetermined voltage to this predetermined voltage.Then, filter capacitor 110 and can measure electric charge between the electric capacity shift to finish before (that is, before sharing end cycle), the guard signal 103 that is applied to guard electrode 106 can change to the protection voltage similar to the voltage on the filter capacitor 110.If it is that second of substantially constant voltage is protected voltage and repeatedly carried out the electric charge transfer processing that guard signal 103 changes to during electric charge is shared, and then can be the selected voltage of voltage on the approximate filter capacitor 110.It is suitable should being similar to when using discrete voltages in guard signal 103, because the voltage on the filter capacitor 110 changes during sharing and between the electric charge transfer processing repeats.For example, the protection voltage that is applied to the guard signal 103 of guard electrode 106 can be set to predetermined voltage can measuring between the electric capacity charge period, changes to appropriate threshold voltage (V from predetermined voltage then _TH) and correlation filtering electric capacity 110 on the voltage of back between the voltage that resets, to reduce the net transfer of electric charge.Any DC skew between guard electrode voltage and the sensing electrode voltage can not influence the validity of capacity coupled protection, because similar voltage swing (that is, the similar variation of voltage) is general bigger than the virtual voltage that applies, guarantees effective protection.

Guard signal (V _G) 103 protection voltage can produce with mode arbitrarily.Even the embodiment shown in Figure 1B-C has described by starting switch 114 and applied the guard signal 103 that the I/O of supply voltage produces, it should be understood that it also can is many other embodiment.For example; the optional source that is used for guard signal 103 except digital I/O, can comprise discrete switch, multiplexer, operational amplifier (OP-AMP), follower or ADC; utilize electric current and/or voltage source, and can separate with the controller of implementing the electric charge transfer processing.In addition, in various equivalent embodiment, can also use digital to analog converter, pulse width modulator to wait and produce guard signal 103.In addition, can apply the wide-range voltage that is different from by the use of electric charge transfer processing.For example, being used for the voltage source (if working voltage source, rather than electric current or some other sources) of guard signal 103, even the protection voltage of guard signal 103 itself, can exceed by predetermined voltage and filter capacitor resetting voltage restricted portion.Also to understand, in system, use one or more guard signals with a plurality of guard electrodes 106.In addition, when sensing electrode is in when not being to be used for " passive " of sensing, can use sensing electrode as guard electrode.

In the embodiment shown in Figure 1B-C, guard electrode 106 is connected to suitable protection voltage generation circuit 104.Protection voltage generation circuit 104 suitably comprises one or more switches 114, is implemented as the I/O of controller 102.Although the particular instance of below having described protection voltage generation circuit 104 (for example; in conjunction with Fig. 3 A-E and 4A-E), but circuit 104 is to respond the signal that is applied by switch 114 produces any appropriate of two or more different value voltages on guard electrode 106 circuit.In each embodiment, passive protection net 105 usefulness of circuit 104 comprise conventional passive impedance circuit (for example voltage or the impedance-driven circuit) enforcement of resistance, inductance and/or the capacitor of one or more routines.Show passive protection net 105 and be directly connected to guard electrode 106 in the transducer 100; In other was realized, switch, follower or other element can be mediate.

In one embodiment, guard signal 103 comprises near the voltage that equals the voltage relevant with the electric charge transfer processing.Guard signal 103 comprise near the predetermined voltage that is applied to any " active " sensing electrode with during charge cycle (for example, relevant one or more sensing electrode 112A-C) with measuring electric capacity to " near the voltage of charging " of their chargings.Guard signal 103 also comprises " near the share voltage " that is approximately equal to the relevant voltage of any " active " sensing electrode of sharing with filter capacitor 110 during the cycle of sharing when allowing electric charge to share.In this embodiment, guard signal 103 (that is, before charge cycle finishes) before applying the predetermined voltage end begins and will be applied to guard electrode 106 near charging voltage.Can also apply At All Other Times near charging voltage, for example during the whole charge cycle or during the other parts at charge cycle.When applying near charging voltage is that flexibility is arranged, owing to (for example, 112A-C), and can ignore the influence of guard electrode 106 being coupled to the parasitic capacitance of active sensing electrode at the active sensing electrode of that cycle drive.(for example, 112A-C) with between the relevant filter capacitor 110 share before electric charge finishes, guard signal 103 changes to begin and will be applied to guard electrode 106 near share voltage at any active sensing electrode.With apply near charging voltage similarly, when beginning to apply near share voltage has flexibility.For example, when allowing electric charge can applying near share voltage at the whole duration in this cycle between the active sensing electrode (for example 112A-C) or when only near this end cycle, sharing.In order to make protection effectively, when applying these two approaching protection voltages, generally should provide low relatively impedance.Yet when not applying these two protection voltages, this protection needn't drive with Low ESR always, although can reduce the validity as protection.

Can replenish or revise general purpose transducer and the protection scheme shown in described above and Figure 1B in many different modes.In each embodiment, the electric capacity (not shown) that comprises can be included in the electric charge that removes from each sense channel relevant with sensing electrode 112A-C with interim storage in the protection voltage generation circuit 104.This electric charge of operating period subsequently can turn back to suitable sense channel (generally getting back to electrode 112A-C itself).Described another kind of mode, by the electric charge on the included electric capacity (is for example remained on relative steady state value, by utilizing switch 114 to apply the signal of telecommunication), can reduce the electric charge between filter capacitor 110 and the electric capacity that comprises, shared clean amount by sensing electrode 112A-C.Generally, the electric capacity that design comprises is compared the concrete total capacitance bigger (at least one order of magnitude or bigger) of protection electric capacity between sensing electrode 112A-C and the guard electrode 106, and bigger than relevant filter capacitor 110 usually.In such an embodiment, low-impedance protection signal 103 is avoided and sensing electrode 112A-C and the influence of other electrode coupling arbitrarily relatively because the electric capacity that comprises is bigger.As a result, if the sensing scheme is guaranteed, then single guard electrode 106 can be used for shielding effectively a plurality of sensing electrode 112A-C and is not subjected to undesirable inside and outside coupling, comprises the coupling from a sense channel to another sense channel.As directed, even when being used to produce the switch opens of protection voltage, guard signal 103 also can be a Low ESR and effective.Except described herein those, also can carry out many other enhancings or change.For example, if this output is high impedance, then protect the output of voltage generation circuit 104 can cushion effectively so that the protection to a plurality of sensing electrodes to be provided.

With reference to figure 1C, show exemplary timing scheme 150, its mode that is suitable for utilizing electric charge to shift sensing " switching the RC time constant " is operated the transducer 100 of Figure 1B.Concrete timing scheme 150 shown in Fig. 1 C mainly is applied to the sensing of the electric capacity measured of sensing electrode 112A.Can carry out similar processing to measure the electric charge on the electrode relevant with the electric capacity measured of sensing electrode 112B-C.Should be noted that can measure electric capacity at each shares under the situation of common filter capacitor 110, the sense channel general sequence ground operation relevant and be not the while for this particular instance with sensing electrode.Yet parallel work-flow can be carried out in equivalent embodiment, for example can measure electric capacity at each and provide its oneself filter capacitor 110, or for example coding or frequency modulation(FM) sequence has been applied among the embodiment of independent sense channel.

During " the RC time constant of the switching " sense process shown in the timing scheme 150, the measured electric capacity relevant with sensing electrode 112A utilizes switch 116A to provide charging voltage pulse 201.In this embodiment, switch 116A utilizes the digital I/O of controller 102 to implement.Because digital I/O generally provides logic high and low voltage (for example, V _DdAnd GND), so apply and have predetermined voltage V _DdThe charge voltage pulse very simple.Providing between the charging pulse 201, allowing the measured electric capacity relevant to discharge into filter capacitor 110 via passive impedance 108A with sensing electrode 112A.This passes through V _x117A (at the node place of being coupled to switch 116A corresponding to the voltage on the electric capacity measured relevant) and V with sensing electrode 112A _FThe Voltage trace at 115 (at the node places of being coupled to I/O119 corresponding to the voltage on the filter capacitor 110) illustrates.Vx 117A is elevated to predetermined voltage (for example, V when applying predetermined voltage during charge cycle _Dd), during sharing the cycle, reduces electric charge in filter capacitor 110 time when measuring capacitor discharge then along with the time constant that defines by the electric capacity measured relevant with passive impedance 108A with sensing electrode 112A.Simultaneously, along with being charged during the cycle of sharing by the electric capacity measured relevant with sensing electrode 112A, the voltage on the filter capacitor 110 slowly increases.During the cycle of sharing, V _x117A and V _F115 near same value, because two electric capacity separately are at shared electric charge.In most embodiment, the shared cycle will be provided with long enough can make V _x117A and V _F115 share enough electric charges so that they are basic identical when sharing end cycle.This can make this system not too responsive to regularly changing.

Between in front shared cycle and charge cycle subsequently, optional " current canceling " voltage is applied to measures electric capacity.The timing of control " current canceling " voltage is so that the amount of " parasitism " electric charge that removes from filter capacitor 110 is added to the amount of " parasitism " electric charge of filter capacitor 110 no better than by passive impedance 108A during charge cycle, and can measure electric capacity and still stay suitable charging voltage place before sharing with filter capacitor 110.This allows less value for passive impedance 108A, and allows generally time constant faster, can not measure regularly demand of capacitance charge and can not change.

Provide the I/O pin 119 of the controller 102 of switch 118 also to measure the voltage 115 on the filter capacitor.I/O 119 comprises suitably or comparator (it is can be used to provide signal bits an analog-to-digital quantizer), Schmidt trigger, CMOS threshold values is provided and/or can measures the voltage V of each time (for example 202A-C) when switch 118 is opened _F115 multidigit analog to digital converter parts.When comparator is used for measuring voltage 115, V _THCan summary equal mid point between high and the low logical value to simplify this system.V _THThe chances are has the height of simple exemplary CMOS threshold value and the mid point between the low logical value.

In the specific embodiment shown in Fig. 1 C, the measured electric capacity relevant with sensing electrode 112A is recharged and the voltage V on filter capacitor 110 of discharging _F115 surpass the threshold voltage V relevant with I/O 119 _THWhen I/O 119 senses passing threshold voltage V _THWhen (representing), utilize the switch 118 of I/O 119 that reset signal 203 is provided by a 202C.Switch 118 applies reset signal 203, at voltage V _F115 surpass threshold voltage V _THAfterwards, reset packet is contained in the electric charge on the filter capacitor 110.Fig. 1 C shows and is right after after sharing the cycle and only begins (after the filter capacitor 110 that resetting) " reading " I/O 119 after some of electric charge transfer processing repeat to take place, and measures the voltage on the filter capacitor 110.Yet,, exist other timing and frequency to select to be used to measure the voltage on the filter capacitor 110 and to expect here as previous argumentation.For example, at voltage V _F115 surpass threshold voltage V _THAfterwards, can carry out other electric charge transfer processing and/or carry out other measurement.

Surpass threshold voltage V by following the tracks of from applying the voltage of reset signal 203 on filter capacitor 110 _THThe repeatedly electric charge transfer cycle of carrying out can be determined to measure electric capacity effectively.That is to say that the known charge amount on the filter capacitor 110 of producing is (for example, as by reaching V _THThe voltage at measured node place of filter capacitor shown in) repeat number of the electric charge transfer processing of carrying out can the related effectively actual capacitance that can measure electric capacity.Equally, taking place many times, the vibration number or the resetting of filter capacitor 110 of electric charge transfer processing also can be used for determining to measure electric capacity.

Embodiment shown in Figure 1B-C shows reset signal 203, by being provided with switch 118 is coupled to voltage on the node of filter capacitor 110 of the local system ground connection filter capacitor 110 that resets, so that the both sides of filter capacitor are set to ground connection.In response to reset signal 203, this can drop to V _RESETTrace V _FFind in 115.In other embodiments, resetting of filter capacitor 110 can be finished with multiple mode, and sensor configuration and selected sensing scheme are depended in available selection.In each embodiment, can use the side of reset signal 203 with filter capacitor 110, or the voltage at filter capacitor 110 two ends, be set to the suitable resetting voltage that is fit to sensing.Resetting of filter capacitor 110 also can be finished by the switch on the side of filter capacitor 110 simply is coupled to suitable supply voltage.Alternatively, under the situation of the both sides of filter capacitor 110 by switch control, by apply known voltage on filter capacitor 110 both sides, the voltage on the filter capacitor 110 can reset to predetermined value.In addition, filter capacitor 110 can comprise capacitor network, replace single capacitor, and each capacitor in this net can reset to different voltage and by one or more switch controls, open and close a large amount of switches so that the filter capacitor 110 that resets can relate to.

Can be periodically, aperiodicity ground or reset signal 203 otherwise is provided, and/or do not provide reset signal 203 in certain embodiments with " resetting " transducer.Yet such system still demonstrates " resetting voltage " of thinking to be used to protect purpose.For example, other embodiment that utilizes RC to net does not have the equivalent of the active switch that resets 118 (being shown in Figure 1B) that is used for correlation filtering electric capacity.This system can instead allow voltage on the correlation filtering electric capacity with by allowing electric charge to shift " resetting voltage " of thinking to be used to protect purpose around by the passive impedance q.s.As another example, the approaching upper and lower threshold value of " charging " and " discharge " electric charge transfer processing that some embodiment utilizations that utilize oscillator or double slanted to change replace, and must not reset; Under these circumstances, go up or lower threshold value in one or both of all think to be used to protect " resetting voltage " of purpose.The 3rd example comprises the sigma-delta processing that is used for capacitance sensing, and wherein the output of sigma delta quantizer approximately remains on the feedback threshold, and this feedback threshold thinks to be used to protect " resetting voltage " of purpose.These only are several examples of other system, and other system is not had the seedbed to reset, or even in fact reset, but still demonstrate " resetting voltage " of thinking to be used to protect purpose.

Equally, predetermined charging voltage also can change and is used for specific sensing system, but this system still demonstrates " predetermined charge voltages " of thinking to be used to protect purpose.For example, utilize the embodiment of " charging " and " discharge " circulation can have the predetermined charge voltages that the relative electric charge of two or more generations shifts.In these cases, " charging " predetermined charge voltages and " discharge " predetermined charge voltages can be used to define guard signal 103.

In each embodiment, the voltage that " threshold value " voltage is measured by the A/D on the filter capacitor (or represent on the filter capacitor voltage) or suitable definite any other voltage replace.Shift the number that repeats and/or be suitable for final voltage on the filter capacitor of selected sensing scheme by following the tracks of electric charge, can determine to transfer to the quantity of electric charge of filter capacitor from measuring electric capacity.This quantity of electric charge is corresponding to the value that can measure electric capacity.Have again, optional embodiment can utilize other electric charge transfer scheme, comprise that the sigma of any kind-delta handles, filter capacitor 110 is via measuring electric capacity charging and " Delta " charge discharge by the impedance (not shown) thus, and vice versa or the like.

Have many selections of effective guard signal 103, and four this selections are by trace 204 (V _G0), 205 (V _G1), 206 (V _G2) and 208 (V _G3) be shown among Fig. 2 A.Trace 204 shows " sensor matching " and selects.During the electric charge that applies the predetermined voltage step and the electric charge transfer processing of the transducer of the time constant technology of utilizing conversion is shared step; should " sensor matching " select to be used to make voltage and expection voltage (for example, the voltage V on the sensing electrode 112A that can measure on the electric capacity on the guard electrode (for example 106) _X117A) coupling.Trace 205 shows another " sensor matching " and selects, and it can be used for mating the expectation voltage that can measure on the electric capacity during the electric charge that applies predetermined voltage step and the electric charge transfer processing of utilizing the system with switch-capacitor technology little or insignificant time constant is shared step.Each repetition that trace 206 shows for the electric charge transfer processing can be used for selecting near " the switched voltage distributor " that can measure the expectation voltage on the electric capacity.Trace 208 shows " pulse code modulation " signal, and it can be used for repeatedly carrying out near the expectation voltage that can measure on the electric capacity in the electric charge transfer processing.As by shown in the trace 208, the influence of pulse code modulation be the protection voltage of guard signal 103 not along with the each execution transition of electric charge transfer processing, but still following pattern.

It should be understood that can be synchronously or carry out polytype electric charge transfer processing continuously.For example, can use a plurality of similar electric charge transfer processing, to determine a plurality of electric capacity of measuring simultaneously or continuously.Also can use a plurality of similar electric charge transfer processing to determine for more accurate on the whole simultaneously, obtain identical a plurality of definite of electric capacity that measure.Also can use summary is relative in fact each other electric charge transfer processing with the more complicated measurement scheme of practice.For example, the first electric charge transfer processing can be used for the filter capacitor that charges, the second electric charge transfer processing same filter capacitor that can be used for discharging; One or many is measured the value that can carry out and be used for determining to measure electric capacity at the charging and the interdischarge interval of filter capacitor.Having this charging and discharge scheme is being useful aspect the influence that reduces environment change.

Polytype electric charge transfer processing (having relevant protection voltage) can also be used to strengthen the effect of protection.For example, pulse code modulation can be thought the stack of (with relevant protection voltage) of polytype electric charge transfer processing.Pulse code modulation can be thought to repeat electric charge transfer processing (with relevant protection voltage) a kind of, two or more types with specific order thus.These dissimilar electric charge transfer processing (with relevant protection voltage) can be used identical predetermined voltage and use identical parts, but can relate to different guard signals.For example; the first electric charge transfer processing (with relevant protection voltage) can comprise the first protection voltage and be different from the second protection voltage of the first protection voltage, and the second electric charge transfer processing (with relevant protection voltage) can comprise the 3rd protection voltage and the 4th protection voltage.In this example, the 3rd protection voltage can be identical with the first protection voltage or the second protection voltage.Equally, the 4th protection voltage can be identical with the first protection voltage or the second protection voltage.And the 3rd protection voltage and the 4th protection voltage can be identical or different.The timing of protection voltage and value can be by being suitable for protecting the average protection voltage swing of applicable sensing electrode to determine.

For the embodiment shown in Figure 1B-C, for guard signal 103 with trace 204 (V _G0) selection that illustrates can follow the tracks of the voltage that can measure on the electric capacity to help prevent net charge since protection electric capacity on filter capacitor 110, obtain or lose.Demonstrate the voltage of the voltage that " constant switching time " detection technology that similar utilization for example describes among Figure 1B-C demonstrates by the active sensing electrode in the transducer (for example 112A-C) by this " sensor matching " guard signal shown in the trace 204.For example, can dispose the voltage V that is chosen as the measured electric capacity relevant by the guard signal shown in the trace 204 with the sensing electrode 112A shown in Fig. 1 C _XThe desirable voltage of 117A roughly the same (for example electric capacity 408 is similar to the electric capacity measured relevant with sensing electrode 112A among Figure 1B and the ratio of filter capacitor 110 with the ratio of electric capacity 404 among Fig. 4 A by selecting).The first protection voltage of guard signal 103 is near the voltage of charging pulse 201, and along with by V _XIt is similar or than its time constant faster that 117A demonstrates, the second protection voltage attenuation of guard signal 103 to and V _F115 similar voltages.The second protection voltage of guard signal 103 also changes when carrying out the electric charge transfer processing, so as the term of execution of those of electric charge transfer processing, to have near and V _XThe overall rising of the rising that 117A is relevant (and this rate of change of the second protection voltage of electric charge transfer processing execution can be thought another time constant of this system).Select to utilize and carry out the similar circuit of the employed circuit of electric charge transfer processing by transducer 100 or by the guard signal shown in the trace 204 by other circuit generation similar to other charge-sensing circuit.By energizing switch electric charge is transferred to and to be produced the circuit that this " sensor matching " selects on the applicable protection electric capacity and method is shown among Fig. 3 A-3C, the 4A-C and further discuss below.

With single shared cycle relevant by the selection shown in 204 during, be used for the selection shown in the trace 205 of guard signal 103 and demonstrate the more discrete variation of protection voltage, and lack tangible time constant feature.(it has the seedbed to switch the electric charge that can measure between the electric capacity filter capacitor relevant with it to share to utilize the electric charge transfer processing, replacement does not have the seedbed by passive impedance and allows electric charge to share), be somebody's turn to do " switch-capacitor " of trace 205 selects " switch-capacitor " of similar sensing system to select.Selection shown in the trace 205 applies the second protection voltage; this second protection voltage keeps constant relatively during the single shared cycle but at a plurality of shared cyclomorphosises, " switch-capacitor " type technology that is used for its electric charge transfer processing as utilization is found at transducer.By energizing switch electric charge is transferred to the circuit and the method that are used for the selection of this " switch-capacitor " of generation on the applicable protection electric capacity and be shown in Fig. 3 C, 4C and further argumentation below.

It is favourable that these " sensor matching " of being used for guard signal 103 are selected than the selection with " simpler " waveform (for example shown in the trace 206 and 208); be that they can be used to reduce for each execution electric charge transfer processing because guard electrode is transferred to the electric charge of filter capacitor; and be not only the net charge that during the process of carrying out the electric charge transfer processing, shifts, caused to measure determining of electric capacity.This is to promote by the second protection voltage that changes during the repetition of electric charge transfer processing.Yet; if 110 the electric charge net transfer that guard signal 103 occurs the term of execution of being minimized in this group electric charge transfer processing from guard electrode 106 to filter capacitor; then guard signal 103 all is effective arbitrarily; this group electric charge transfer processing finally causes the one or many of the voltage on the filter capacitor 110 to be measured, and this is used for determining to measure electric capacity.This comprises the guard signal selection, the electric charge transfer processing that its coupling is different with the electric charge transfer processing that sensing system uses or do not match electric charge transfer processing and simply swing (following argumentation) between two or more substantially constant voltages.

In many examples; it generally is actual that guard signal 103 is applied to guard electrode 106; it can not be minimized in single and carry out the electric charge of transferring to filter capacitor 110 during the electric charge transfer processing from guard electrode 106; but can be minimized in the net transfer of the electric charge during this group electric charge transfer processing; this group electric charge transfer processing finally causes the one or many of the voltage on the filter capacitor 110 to be measured, and this is used for determining the applicable electric capacity of measuring.This can finish with guard signal 103; this guard signal 103 causes the term of execution of the one or many of electric charge transfer processing the electric charge on the first direction between guard electrode 106 and the filter capacitor 110 to shift, and causes the electric charge on the second direction of relative first direction term of execution of other of electric charge transfer processing to shift.

Shown in Fig. 2 B, transfer to from guard electrode in the cycle of sharing during magnitude of voltage 253 less than second protection and transfer to the electric charge that to measure on the electric capacity in the shared cycle from guard electrode when the electric charge that can measure on the electric capacity is used in the voltage that can measure on the electric capacity greater than the second protection magnitude of voltage 253 and recover effectively when measuring voltage on the electric capacity.Fig. 2 B also shows guard signal 103, and this guard signal 103 is included in predetermined voltage and is applied to the first protection voltage 251 and the second protection voltage 253 in the duration in the time can measuring electric capacity and share in duration in the time of can measuring electric capacity.In Fig. 2 B, guard electrode 106 and the electric charge transfer that can measure between the electric capacity illustrate with arrow 230A-G.Arrow 230A-C represents that electric charge transfers to cycle can measure electric capacity the time from guard electrode 106, and arrow 230E-G represents that electric charge transfers to the cycle of guard electrode 106 from measuring electric capacity.Because voltage 117 is equivalent to the second protection voltage 253 substantially during this shared cycle, so insignificant electric charge shifts at arrow (it shows as a little) 230D place.Specific magnitude of voltage V _{G_HIGH}251 and V _{G_LOW}253 can significantly change to another embodiment from an embodiment.Utilize this method, the net charge of transferring to filter capacitor owing to the effect of protection electric capacity is considerably less with respect to the total electrical charge on electrode during the electric charge transfer processing, so that can think to approach zero.Electric charge between balanced protection electric capacity during the execution sequence of electric charge transfer processing and filter capacitor 110 shifts and can further extend beyond the example discussed and such extension here within the scope of the present invention.

For example, a kind of selection that is used for guard signal 103 will swung between the voltage near the first protection voltage of predetermined voltage with near second protection of the average voltage on the filter capacitor 110.For the average voltage of definite filter capacitor 110, the voltage on this group electric charge transfer processing period average filter capacitor 110, the measurement that this group electric charge transfer processing causes and produce the voltage on the filter capacitor 110, this measurement are used for determining to measure electric capacity.Given class value for the electric capacity measured that is used to expect, filter capacitor, predetermined voltage, resetting voltage, threshold voltage; and the effect of ignoring (if or module allow to describe) any passive impedance, can use known method to simulate this circuit and determine that average filter capacitor voltage will minimize the effect of any protection electric capacity and the effective second protection voltage is provided.This average filter capacitor voltage obtains on discrete point, and the chances are resetting and be used for determining measuring the average of carrying out the voltage on the filter capacitor 110 that the electric charge transfer processing obtains between the last measurement of filter capacitor 110 of electric capacity at filter capacitor 110.Often, that the chances are is linear for the change in voltage on the filter capacitor 110, so that average filter capacitor voltage is near the mid point between resetting voltage and the threshold voltage.

Be also noted that these capacitance sensors are sampler (in fact or effectively).For example, in the embodiment shown in Figure 1B-C, when not applying predetermined charging voltage, filter capacitor 110 only during the discrete shared cycle with can measure electric capacity and share.In addition, can measure usually on the electric capacity voltage also when electric charge is shared end cycle near the voltage on the filter capacitor 110 115.Therefore; only in the time can measuring voltage on the electric capacity and finish (when applying predetermined voltage and stop) and electric charge at charge cycle and share end cycle during quilt " sampling ", the electric capacity of voltage can measure on to(for) the voltage matches of the guard signal 103 that is applied to guard electrode 106 is enough.The end that electric charge is shared the cycle appears when beginning in the time constant system that is applied to for example switching shown in Figure 1B-C of predetermined voltage; For example in the capacitor system that switches, the electric charge end in shared cycle can appear during from reference voltage decoupling arbitrarily in the time can measuring electric capacity from the filter capacitor decoupling or when filter capacitor.In other words, share if electric charge occurs by passive shared system, then technical electric charge is shared always; Yet, being used to protect purpose, the electric charge cycle of sharing is only thought to continue until with after-applied predetermined voltage (sharing the end of thinking to be used to protect purpose when electric charge).On the contrary, switch the end that has defined the shared cycle of electric charge if switch generation the seedbed coupling to be arranged and allow shared electric charge by measuring, then to think with filter capacitor.

For this reason, can use selection by the guard signal 103 shown in trace 206 and 208.In selecting by " switched voltage distributor " shown in the trace 206; actual guard signal 103 can be between the first protection magnitude of voltage 251 and the second protection magnitude of voltage 253 alternately, and the second protection magnitude of voltage 253 is near " on average " value of the voltage on the filter capacitor 110 115.Although this average V _FSelection is called " switched voltage distributor " to be selected, but does not need voltage divider; For example; when the first and second protection magnitudes of voltage 251 and 253 are supply voltages, are the voltage by another part acquisition of DAC or transducer; or the voltage that utilizes the circuit except that voltage divider to produce, just can obtain the first and second protection magnitudes of voltage 251 and 253 without any need for voltage divider.Simple " switched voltage distributor " term that uses is because use the voltage divider circuit that switches probably in many embodiment of the guard signal of the type.In the embodiment that Figure 1A-B describes, the charging voltage that the first protection magnitude of voltage 251 can equal to be scheduled to, the second protection magnitude of voltage 253 can be near the threshold voltage (V that equals to be used to measure filter capacitor and resetting voltage _TH) mean value.Be used for producing the circuit and the method for being somebody's turn to do " voltage divider of switching " and be shown in Fig. 3 D-E, 4D-E and further argumentation below.

The timing of guard signal 103 is based on the timing that is applied to the pulse 201 that can measure on the electric capacity; guard signal 103 has the first protection magnitude of voltage 251; and charging pulse 201 is applied to and can measures electric capacity, and guard signal 103 has the second protection magnitude of voltage 253 during the electric charge between the pulse 201 is shared the cycle.This regularly is useful, because guard signal 103 can drive by the existing clock in the system.Yet in fact, as long as the first protection magnitude of voltage began to apply before the end of relevant charging pulse 201, even only begin to apply the first protection magnitude of voltage 251 sometimes after 201 beginnings of relevant charging pulse, guard signal 103 can also be effective.Equally, as long as began to apply this second protection magnitude of voltage 253 before electric charge is shared end cycle, do not protect magnitude of voltage 253 even do not apply second for the whole shared cycle, guard signal 103 also is effective.The timing of guard signal 206 is because many former thereby just in time do not mate with charging pulse 201.For example, can measure between electric capacity and the filter capacitor before electric charge shares beginning, coarse timing can cause guard signal 103 to begin to change to the second protection voltage, so that protection is not too effective; In order to reduce the influence regularly of this inaccuracy, wish the part of extensive protection signal 103.

Trace 208 shows the optional embodiment of the guard signal 103 that can realize with less parts.For example, the single I/O that does not have other parts can be used to generate trace 208, shown in Fig. 4 F.Has the selection shown in the trace 208; replace applying the first protection magnitude of voltage 251 that is used for each charging pulse 201; can ignore one or more variations of guard signal 103 to second protection magnitudes of voltage 253; the average swing of the protection voltage that applies with adjusting, and minimize the net charge of transferring to filter capacitor (for example 110) by protection electric capacity.That is to say; apply the duration of a protection magnitude of voltage (for example protection of second in the trace 208 magnitude of voltage 253) by prolongation; replace being converted to another protection magnitude of voltage (for example to the first protection magnitude of voltage 251), can use with the similar mode of pulse code modulation (also being called " pulse frequency modulated ") and revise the average protection voltage swing that is applied to guard electrode 106.That is to say,, compare, reduced the average amplitude of oscillation of the protection voltage 103 on the guard electrode 106 with applying more multifrequency charging pulse by applying less frequency charging pulse (for example, prolonging voltage 251 and/or voltage 253) and having less transformation.Notice that average protection voltage swing can keep the ratio scale with the predetermined charge voltages amplitude of oscillation in a plurality of circulations, to suppress the high performance of maintenance by improving power supply noise.Be used for generating the circuit and the method for being somebody's turn to do " pulse code modulation " selection and be shown in Fig. 3 D-E, 4D-E and further argumentation below.

Basic structure shown in Figure 1B-C and operation are carried out many changes.For example, timing scheme 150 hypothesis electric charges shown in Fig. 1 C are transferred to filter capacitor 110 from the electric capacity measured " forward " relevant with sensing electrode 112A, and equivalent embodiment can (that is to say based on share electric charge on relative direction, positive charge can be placed on the filter capacitor 110, it pulls to the relevant electric capacity measured with sensing electrode 112A by impedance 108, then pulse 201 discharges that provide by switch 114).Alternatively, the sensing scheme based on threshold value shown in Fig. 1 C can replace with the measurement scheme of any kind, is included in after the electric charge transfer processing of carrying out predetermined quantity, based on the voltage 115V on the filter capacitor 110 _FAny technology of measurement.And, be used for charge or discharge can measure the pulse 201 of electric capacity needn't constant duration or have the equal duration.In fact, in many examples,,, controller 102 measuring interruption or other traction of handling the arbitrfary point here so can handling in fact because the many embodiment that illustrate stand variation regularly easily.This is genuine when surpass the time constant that is used to settle sample time especially.Alternatively, the time interval of having a mind to change pulse 201 can make the sampling frequency spectrum extend to better acceptable noise.

Can carry out many changes to basic structure shown in Fig. 2 A-B and operation.Timing scheme 200 shown in Fig. 2 A shows the first protection voltage, and that the chances are is constant, and if this change, the second protection voltage changes.Yet; (first and second protections poor between the voltages because protection voltage " amplitude of oscillation "; except that the transient period) greater than the protection magnitude of voltage of reality; so replace the second protection voltage; guard signal 103 also can change with the first protection voltage to be realized, or the first and second protection voltages changes realize.Equally, as previous argumentation, be used to protect the timing of change in voltage to have big flexibility.

Forward Fig. 3 A-E now to, show each embodiment (circuit 104A-E) of protection voltage generation circuit 104.Circuit 104 can comprise many impedances and switch and as suitablely utilize many reference sources.For example, each impedance shown in Fig. 3 A-D can be represented because the impedance that single parts or a plurality of component netlist cause.Active parts except switch, for example multiplexer, DAC, current source or OP-AMPS can also be included in the protection voltage generation circuit 104, but do not need in most embodiment and do not use described active parts.In addition, for example, the switch of protection voltage generation circuit 104 can be discrete arbitrarily switch or relay, perhaps corresponding to any conversion or the multiplexed function that are included in the aforesaid controller 102.The switch that is used by voltage generation circuit 104 can utilize the I/O pin of controller 102 to be embodied as switch 114.The output of an I/O can provide a plurality of switches sometimes; For example, can provide the digital I/O of supply voltage and high impedance status to can be used for the functional of two switches a variable connector being provided or being coupled to a node.Numeral I/O also can provide pull-up resistor or pull down resistor or current source.

Can provide the I/O of switch and measurement function to realize arbitrary switch if utilize, then sensing system has the increase selection of fetch protection signal 103.The voltage that offers guard signal 103 that this allows system responses to read in it is dynamically regulated guard signal 103 (if the pulse code scheme is available, then for example by changing pulse code).

The impedance of circuit 104 can be resistance, inductance, electric capacity and/or other impedance component of any conventional.Thus, the voltage at the impedance two ends in the circuit 104 can be connected to the historical influence formerly of the node of impedance.Should " formerly historical " influence be significant especially, and control this and influence and define guard signal 103 for electric capacity and inductance element.Provide the reference source of reference example such as reference voltage can be in the inside or the outside of controller 102.Reference that can be easy-to-use.For example, reference voltage can pass through supply voltage (V _Dd, GND ,-V _Dd) or cell voltage etc. provide, and the actual reference voltage that uses can be directly from source or some modification of these voltages that pass through impedance adjustment.In the example shown in Fig. 3 A-E, for convenience of explanation, showing a reference voltage is reference voltage 301, and showing second reference voltage is local system ground connection; As previous argumentation, produce circuit 104 by guard signal and can use other reference voltage level easily.

Fig. 3 A shows the configuration of the protection voltage generation circuit 104A that comprises the passive protection net, and this passive protection net comprises three impedances 304,306,308.Three impedance 304,306,308 series connection are located between reference voltage 301 and the ground.Switch 302 and impedance 304 are in parallel and switch 303 is in parallel with impedance 308.(as previous argumentation, as suitable, switch 302 and 303 may be embodied as the switch 114 of Fig. 1).In the embodiment shown in Fig. 3 A, can provide guard signal 103 by diverter switch 302,303 suitably.Close and switch 303 when opening when switch 302, determine the voltage of guard signal 103 by the voltage at reference voltage 301 and impedance 306 and 308 two ends.This voltage of guard signal 103 is corresponding to the resetting voltage of protected electric charge transfer processing.When switch 302 and 303 was opened, this voltage of guard signal 103 was determined by the voltage at reference voltage 301 and impedance 304,306 and 308 two ends.This voltage of guard signal 103 is corresponding to the voltage on the filter capacitor in the protected electric charge transfer processing.Open and switch 303 when closing when switch 302, the driven that makes guard signal 103 is to GND.This voltage of guard signal 103 is corresponding to the predetermined charge voltages of protected electric charge transfer processing.Utilize the appropriate impedance of selecting 304,306,308, for example the configuration of circuit 104A allows to utilize the protection voltage generation circuit of " constant switching time " technology emulation voltage relevant with the electric charge transfer processing, for example in Figure 1B-C.For example, it is corresponding with the filter capacitor that is formed by component netlist to dispose impedance 304, and impedance 304 can be coupled to more than one voltage with accurately corresponding to the voltage of the filter capacitor of coupling.Notice that various resetting voltages and charging voltage can be protected, although they need different transfer sequence or reference voltage (for example, V _DdAnd ground).

For the embodiment shown in Fig. 3 A, to open and switch 303 when opening when switch 302, impedance 304,306 and 308 forms the impedance distributor with " common node ", and its middle impedance 306 is connected to impedance 308 and impedance 304 is connected to impedance 306.When switch 302 cuts out and switch 303 when opening,

impedance

306 and 308 forms the different impedance distributors with common node that impedance 306 is connected to impedance 308.

The impedance distributor is made of the passive impedance of two series connection at least, and each passive impedance all is coupled at least two nodes.Are common (two impedances are connected to " common node ") one of in these nodes for these two impedances.Common node is as the output of impedance distributor.The output of impedance distributor be along with the time at " non-share " node (not being the node of two impedances of common node) voltage of locating to apply and/or the function of electric current.The simplified example of impedance distributor is by two electric capacity or two voltage dividers that resistance constitutes.More complicated impedance distributor can have unmatched electric capacity, resistance or the inductance of serial or parallel connection.An impedance also can have any combination of electric capacity, resistance and inductance feature.

In the one exemplary embodiment of the protection voltage generation circuit 104B shown in Fig. 3 B, the passive protection net is made of impedance 314.For circuit 104B, when switch 312 cut out, guard signal 103 was suitably switched by the switch between reference voltage 301 and the guard signal 103 312; This voltage of guard signal 103 is corresponding to predetermined charging voltage.When switch 312 was opened, guard signal 103 suitably switched to second voltage by the voltage definition at impedance 314 two ends; This voltage of guard signal 103 is corresponding to the voltage on the filter capacitor.Can off switch 313 to remove electric charge from impedance 314; This voltage of guard signal 103 is corresponding to resetting voltage.Utilize the appropriate impedance of selecting 314, the configuration of circuit 104B allows to utilize the protection voltage generation circuit of " constant switching time " technology emulation of sigma-delta form voltage relevant with the electric charge transfer processing.

Fig. 3 C shows another embodiment of the protection voltage generation circuit 104C that comprises the passive protection net that is made of two impedances 324,326 of connecting.Circuit 104C is driven by three switches 322,323 and 325.Close and switch 323 and 325 when opening when switch 322, guard signal 103 is reference voltages 301; This voltage of guard signal 103 is corresponding to predetermined charging voltage.Open and switch 325 when closing when

switch

322 and 323, guard signal 103 is determined by the voltage at reference voltage 301 and impedance 324,326 two ends; This voltage of guard signal 103 is corresponding to the voltage on the filter capacitor.When

switch

323 and 325 cuts out and switch 322 when opening, guard signal 103 is GND and removes electric charge in the impedance 326; This voltage of guard signal 103 is corresponding to resetting voltage.Open and switch 325 when closing when

switch

322 and 323,

impedance

324 and 326 is formed on the impedance distributor that guard signal 103 outputs place have common node.Utilize the

appropriate impedance

324 and 326 of selecting, for example the configuration of circuit 104C allows to utilize the protection voltage generation circuit of " switch-capacitor " technology emulation voltage relevant with the electric charge transfer processing.

Fig. 3 D shows the embodiment of the protection voltage generation circuit 104D with passive protection net, and this passive protection net comprises two impedances 334 and 336 with switch 332 located in series of reference voltage 301 and ground connection (GND).In circuit 104D, utilize suitably switch protecting signal 103 of switch 332.When switch 332 was opened, guard signal 103 was determined by the voltage at reference voltage 301 and impedance 334 two ends; This voltage of guard signal 103 is corresponding to predetermined voltage.When switch 332 cut out, guard signal 103 was determined by the voltage at reference voltage 301 and impedance 334 and 336 two ends; This voltage of guard signal 103 is corresponding to the average voltage on the filter capacitor.When switch 332 cut out, impedance 334 and 336 formed the impedance distributor, and it suitably divides reference voltage 301, as being determined by the type and the value of selected impedance compoment.That is to say that impedance 334 and 336 is suitably as " on draw " parts when switch 332 is opened, and impedance 334 and 336 is used as the impedance distributor when switch 302 cuts out.Be used at resistance under the simple scenario of impedance 334 and 336, the impedance distributor be conventional voltage divider and when switch 332 cuts out guard signal 103 be directly proportional with reference voltage 301 with the ratio of the resistance sum of impedance 334 and 336 via the resistance of impedance 336.Utilize the appropriate impedance 324 and 326 of selecting, for example the configuration of circuit 104D allows to be used for the protection voltage generation circuit 104 of " switched voltage distributor " type guard signal 103.Can further adopt the output of circuit 104D, modulating frequency for example is used for the waveform of " pulse code modulation " type of guard signal 103 with generation.

Fig. 3 E shows another embodiment that guard signal produces circuit 104E, and this guard signal produces circuit 104E and comprises two

switches

342 and 343 that are coupled to reference voltage 301 and ground respectively, and does not have discrete impedance.In the embodiment of 104E, the passive protection net can comprise simple lead thus.In circuit 104E, guard signal is closed and switch 343 reference voltage 301 and open and switch 343 suitably switches between the ground connection when cutting out at switch 342 when opening at switch 342.The configuration of circuit 104E allows protection voltage generation circuit 104 that " voltage divider that is converted " type guard signal 103 (wherein not having voltage divider and guard signal switch between unallocated reference voltage 301 and ground) of degeneration is provided.The configuration of circuit 104E is especially useful for the waveform of " pulse code modulation " type of guard signal 103, wherein be used to detect stimulus 101 all to repeat electric charge transfer processing synchronous, guard signal 103 does not change voltage.

The embodiment of the protection voltage generation circuit 104 shown in Fig. 3 A-3E is five examples that can be used for each possibility of definite guard signal 103.Here expection utilizes to be had and not have by connecting and/or the switch of the passive protection net that parallel impedance constitutes provides many other selections of guard signal 103.Shown in these possibilities and Fig. 3 A-3E those are quite similar.For example, other impedance can be coupled to impedance 306 another reference voltage in parallel with the impedance 304 of circuit 104A.As another example, place of switches 313, the impedance 314 of circuit 104B can be in parallel with switch 312.As the 3rd example, replace coupling impedance 326 to ground, the switch 325 of circuit 104C can be coupled to reference voltage 301 with impedance 324.As another example, the switch 332 of 104D can be coupling between impedance 334 and the reference voltage 301, replaces being coupling between impedance 336 and the ground.The more remarkable difference of other possibility, and comprise other the configuration in impedance and switch.

Forward Fig. 4 A-E to, in conjunction with the controller of Figure 1B for example controller 102 show example with more detailed protection voltage generation circuit 104.Demonstrative circuit 104F shown in Fig. 4 A, be the embodiment of the circuit 104A shown in Fig. 3 A, its middle impedance 304 is embodied as electric capacity 404, impedance 306 is embodied as resistance 406 and impedance 308 is embodied as electric capacity 408, and switch 302 utilizes I/O 402 to implement and switch 303 utilizes I/O403 to implement.The configuration quite similar (Figure 1A) of the configuration of circuit 104F and the circuit of the electric charge transfer processing that is used to realize transducer 100.Electric capacity 408 with can measure capacitance kind seemingly, resistance 406 and passive impedance are similar, and (for example, 108A-C), and electric capacity 404 is similar with filter capacitor 110.The switch 302 that utilizes I/O 402 to implement is similar with switch 118, and utilizes I/O 403 switch of implementing 303 and the switch 116A-C similar (Figure 1B) that utilizes I/O 119 to implement.I/O 403 and I/O 119 similar (Figure 1B) itself.Circuit 104F can drive in one way thus; with coupling electric charge transfer processing; so that guard signal 103 roughly mates the voltage 117 that electric charge shown in Figure 1B-C shifts sense process, and make from guard electrode 106 to filter capacitor 110 electric charge shift minimum in all points of the electric charge transfer processing that is used for sensing.Even utilize circuit 104F to produce the guard signal 103 that is different from voltage 117; if be used for the total electrical charge minimum that between guard electrode 106 and filter capacitor 110, shifts of this group electric charge transfer processing; it is also still very effective, and this group electric charge transfer processing can cause being used for the definite measurement that can measure capacitance.

Example circuit 104G shown in Fig. 4 B is the embodiment of the circuit 104B of Fig. 3 B.Switch 312 and 313 utilizes single I/O 412 to implement, and impedance 314 is embodied as the net with resistance 414 and electric capacity 415.Example circuit 104G can utilize " constant switching time " the method similar methods driving with " an I/O sigma delta " type.In this method; the switch 312 of opening the switch 313 (if it is not also opened) of I/O 412 and cutting out I/O 412 to be to apply reference voltage 301 (it is a predetermined voltage), the switch 312 of opening I/O 412 then with allow electric charge in system any protection electric capacity and electric capacity 415 between share.When closing the switch 312 of I/O 412, by impedance 414 charging capacitors 415.The switch 313 of cutting out I/O 412 can make electric capacity 415 by impedance 414 discharges.Can utilize I/O 412 to measure voltage on the electric capacity 415, and when predetermined voltage being applied to can measure electric capacity the time, words if necessary can reduce this voltage (can directly not influence the capacitance charge transfer of protection) by the switch 313 of closing I/O 412.In this mode, can be with the protection of the voltage control to the second on the electric capacity 415 voltage.Can be used to detect proximity and measure the electric charge transfer processing that can measure electric capacity synchronous, repeat this circulation of at first opening switch 313 and the off switch 312 of I/O 412 and opening switch 312 and the off switch 313 of I/O 412 then.Drive circuit 104G produces guard signal 103 in one way thus, and this guard signal is for example roughly mating the voltage that can measure electric capacity in the electric charge transfer processing shown in Figure 1A B.Circuit 104G can also drive in one way to produce guard signal 103, and this guard signal 103 can be measured the voltage of electric capacity near coupling in single I/O sigma-delta electric charge transfer processing.

Example circuit 104H shown in Fig. 4 C is the embodiment of the circuit 104C of Fig. 3 C.Utilize I/O 422 to implement switch 322 and 323, and utilized I/O 425 to implement switch 325.Impedance 324 is embodied as electric capacity 424, and impedance 326 is embodied as electric capacity 426.Example circuit 104H and " switch-capacitor " circuit are similar, wherein electric capacity 424 (it is a fixed capacity) with can measure capacitance kind like and electric capacity 426 similar with filter capacitor.Example circuit 104H can utilize with the similar method of " switch-capacitor " method and drive.In this method, the switch 323 of cutting out the switch 322 of I/O 422 and opening I/O 422 is to be applied to electric capacity 424 with reference voltage 301 (it is a predetermined voltage in the embodiment shown in Fig. 4 C).Then, open the switch 322 of I/O 422 and close the switch 325 of I/O 425, between electric capacity 424 and 426, share to allow electric charge.Can be used to detect proximity and measure the electric charge transfer processing that can measure electric capacity synchronous, repeat at first to close the switch 322 of I/O 422 and open the switch 322 of I/O 422 then and close this circulation of the switch 325 of I/O 425.After the circulation of right quantity (for example when having carried out the repeatedly execution of the electric charge transfer processing that is used to produce the result who is used for determining measuring electric capacity), the switch 325 that can cut out the switch 323 of I/O 422 and I/O 425 is with the electric charge on the reset capacitance 426.Drive circuit 104G has the guard signal 103 that the first protection voltage and second is protected voltage with generation in one way thus; the first protection voltage is predetermined voltage, and the second protection voltage is substantially invariable in the execution of electric charge transfer processing but raises from resetting voltage in each electric charge transfer processing of carrying out subsequently before resetting.If fixed capacity 424 can be compared with the ratio of filter capacitor with measuring electric capacity with the ratio of electric capacity 426, then in the electric charge transfer processing this guard signal 103 near the voltages that can measure electric capacity.

It is the embodiment of the circuit 104D shown in Fig. 3 D that example guard signal shown in Fig. 4 D produces circuit 104I.Impedance 334 utilizes resistance 434 to implement, and impedance 336 utilizes resistance 436 to implement, and switch 332 utilizes I/O 432 to implement.When the switch 332 of I/O 432 was opened, guard signal 103 was near reference voltage 301.When the switch 332 of I/O 432 cuts out,, guard signal 103 is set to and reference voltage 301 proportional voltages by the ratio of resistance 436 with resistance 434 and 436 sums.Utilize circuit 104I embodiment, can use the average amplitude of oscillation of guard signal 103 near the voltage relevant with measuring electric capacity.For example, for the transducer 100 of Figure 1B, switch 332 that can be by opening I/O 432 and apply reference voltage 301 (for example, it can be a predetermined voltage) and apply the first protection voltage.Then, a switch 332 that can be by closing I/O 432 and a part that applies reference voltage 301 (for example, its can between threshold voltage that can apply and resetting voltage midway) apply the second protection voltage.Utilize the appropriate timing (it has defined them and when and how long has applied toward each other) of the first and second protection voltages and be used for the step of the electric charge transfer processing of sensing; with appropriate resistance and the reference voltage level selected of utilization, 103 of this guard signals can demonstrate the voltage swing of the average voltage amplitude of oscillation of the approaching electric capacity measured that can apply when electric charge shifts execution and effective protection is provided.

The signal 103 of circuit 104I can further adapt to the pulse code modulation of change over switch 332.Frequency by changing conversion and protect transformation between the voltage thus can produce different real protection voltage swings.When but the control of frequency transitions is the time spent, in fact pulse code modulation can be applied to arbitrary circuit 104.Yet near by can measuring under the virtual voltage 117 or its average situation that electric capacity shows, pulse code can be seldom or is had advantage hardly at guard signal 103.

It is the embodiment of the circuit 104E shown in Fig. 3 E that example guard signal shown in Fig. 4 E produces circuit 104J.I/O 422 can be directly connected to guard electrode, so that there is insignificant impedance.The switch 344 and 346 of circuit 104E has utilized single I/O 422 to implement.Close and the switch 343 of I/O 442 when opening when the switch 342 of I/O 422, the reference voltage 301 that guard signal 103 is set to logic " height " (if I/O 442 is conventional digital I/O, then is V for example, _Dd).Open and the switch 343 of I/O 442 when closing when the switch 342 of I/O 442, guard signal 103 is set to the reference voltage (for example, ground) of logic " low ".Utilize the embodiment of circuit 104J, owing to can reference voltage and ground be set by restriction controller 102, so more be difficult to produce guard signal 103 probably with the amplitude of oscillation that is used for each electric charge transfer processing.Therefore, circuit 104J obeys pulse code modulation.Utilize transfer ratio appropriate between the first and second protection voltages (it can be respectively predetermined voltage and ground), for producing average protection voltage swing near guard signal 103 by the average voltage amplitude of oscillation that can measure the electric capacity demonstration.For example; if per five execution for the electric charge transfer processing that detects proximity; guard signal 103 first and second the protection voltages between the conversion three times, then average protection voltage swing be first and second the protection voltages a transformation between voltage swing 3/5ths.

As previous argumentation, utilizing the parts that also have measurement capability to produce among all example 4A-4E of conversion, for example utilize the digital I/O of controller, if necessary, I/O can also be used to measure the voltage of guard signal 103 to regulate guard signal 103.Be used to produce this group electric charge transfer processing of one or more measurements for current execution, described adjusting can take place, and wherein said one or more measurements are used for determining measurable electric capacity, or for next group electric charge transfer processing, described adjusting can take place.

As mentioned above, can utilize the combination in any of for example conventional integrated circuit of commercial obtainable parts and discrete resistors and/or capacitor to implement many embodiment described herein easily.Since simple, many sensors of various types 100 can be produced, and it shares or does not share various parts and/or switch.For example, be capacitively coupled to total filter capacitor 110 with relevant the measuring of sensing electrode 112A-C among Figure 1B, but in fact each passage can be coupled to the filter capacitor 110 of himself.Equally, in optional embodiment, between sense channel, share one or more passive impedance 108A-C and/or many switches (for example 114,116A-C, 118) and I/O (for example, I/O 119).Can adopt this to share at many other passage two ends to set up many transducers of measuring electric capacity that effective sensing has single controller 102.Should share the cost and the size that can reduce integral sensors 100 significantly.

By on total controller 102, implementing a plurality of sense channel, can realize many usefulness.Usually, go up formation sensing electrode and/or guard electrode easily at the printed circuit board (PCB) (PCB) of standard, it is relatively inexpensive therefore to duplicate these elements on the manufacturing meaning.Can measure under the relatively little situation of electric capacity in hope, then filter capacitor 110 also can be made in PCB.In addition, can on PCB, not form, form one or more resistance, electric capacity and inductance to be provided at the impedance of using in the protection voltage generation circuit 104, for example electric capacity 404 of circuit 104F and resistance 406.As a result, utilize conventional manufacturing technology and structure can implement many different characteristics described above easily.Yet in some cases, in many examples, for example the parts of filter capacitor and/or passive impedance and other impedance can be enough big or need closely enough tolerance limits to guarantee discrete parts.Under those situations, the available one or more discrete capacitors of these parts (for example, filter capacitor 110), resistance, inductance and/or other discrete parts are implemented.

And, even can pass through sum and the number of components that service time, frequency, coding or other multiplexing technique further reduce required signal pin (for example, the pin of ADC and I/O).

Also allow to design many sensors of various types layouts (comprise can be in one dimension, bidimensional or multidimensional sensing touch the multidimensional layout of finding in the pad) with many patterned arrangement sensing electrode 112A-B.Alternatively, a plurality of " button-type " touch sensors and button-type are formed by various passages easily with the combination of touching pad type input unit, perhaps can produce many other sensor placements.

As mentioned above, be used for determining that the apparatus and method of electric capacity especially can be applicable to the proximity transducer device.Forward Fig. 5 now to, calcspar shows the exemplary electronic system 10 that is coupled to proximity transducer device 11.Electronic system 10 refers to personal computer, portable computer, work station, personal digital assistant, TV game player, communicator (comprising radio telephone and information receiving device), the mediation device of expression any type, comprises that register and player (comprising TV, cable box, music player and enlarger) maybe can accept user's input and other device of process information.Therefore, each embodiment of system 10 can comprise processor, memory or the display of any type.In addition, the element of system 10 can be via bus, network or other wired or wireless connection communication.Proximity transducer device 11 can be by the interface or the connection of any type, comprise I2C, SPI, PS/2, USB (USB), bluetooth, RF, IRDA or a plurality of non-limiting examples of the wired or wireless connection of other type arbitrarily, be connected to system 10.

Proximity transducer device 11 comprises controller 19 and sensing region 18.By measuring final electric capacity, proximity transducer device 11 is for the position sensing of the contact pilotage in sensing region 18 114, pointer and/or other input object." sensing region " 18 used herein refer to be included in widely proximity transducer device 11 tops, on every side, among and/or near any space, the wherein position that transducer can inspected object.In the embodiment of routine, sensing region 18 extends a distance and enters the space and prevent object detection until signal to noise ratio from the surface of transducer on one or more directions.This distance can be less than one millimeter, several millimeters, several centimetres or the more order of magnitude, and can significantly change along with the type and the desirable precision of the size of sensing electrode, employed location sensing technology.Therefore, the flatness of specific sensing region 18, size, shape and exact position will change to another embodiment widely from an embodiment.

During work, proximity transducer device 11 is by measuring the position that the measured electric capacity relevant with other input object in a plurality of electrodes and finger piece or the sensing region 18 suitably detects contact pilotage 14, and utilize controller 9, the electrical or electronic marker of position is provided to electronic system 10.System 10 suitably handles this mark to receive the input from the user, with moving hand on display or other object, or is used for any other purpose.

In the general enforcement of contact-sensing apparatus, generally apply voltage and produce electric field to stride across sensitive surface.11 in capacitive proximity sensors device comes the position of inspected object by detecting the capacitance variations that is caused by electric field change, and this electric field change is owing to this object causes.For example, the transducer of proximity transducer device 11 can use the array of capacitive sensing electrode to support many sensing regions.As another example, this transducer can use the capacitive sensing technology to support identical sensing region or different sensing regions with the combination of resistance sensing technology.According to the detection technology that is used for the inspected object motion, the condition of work of the size and dimension of sensing region, desirable performance, hope etc., proximity transducer device 11 can be implemented with multitude of different ways.Detection technology can also change with the type of the information that provides, for example provide " one dimension " positional information (for example along sensing region) as scalar, " bidimensional " positional information (for example horizontal/vertical, dihedral/radial, or across any other axle of bidimensional) as the combination etc. of value.

Controller 19 (it often is called proximity transducer processor or touch sensor controller) is coupled to this transducer and electronic system 10.Usually, controller 19 utilizes any technology in the various technology described above to measure electric capacity and communicate by letter with electronic system.Controller 19 can carry out various other processing to the signal that receives from transducer to realize proximity transducer device 11.For example, independent sensing electrode can be selected or connect to controller 19, detect existence/proximity, calculating location or movable information, and reported position or motion near threshold value the time, and/or and it is being reported to electronic system 10, or give before the user explanation with its indication and wait for and effectively pat/impact/portray/button/make a sign with the hand.Controller 19 can also determine when some type of object of which movement or combination take place near this transducer.

In this manual, definition term " controller " comprises one or more treatment elements, and described one or more treatment elements are suitable for carrying out described operation.Thus, controller 19 can comprise reception from the electric capacity of the signal of telecommunication of transducer, measuring transducer top electrode and with one or more integrated circuits, firmware code and/or software code that electronic system 10 is communicated by letter in all or part of.In certain embodiments, the element that comprises controller 19 will have transducer or be positioned near the transducer.In other embodiments, some elements of controller 19 can be that other element with transducer and transducer 19 can be positioned on the electronic system 100 or is positioned near the electronic system 100.In this embodiment, minimum processing can be carried out near transducer, and most processing is carried out on electronic system 10.

Have, when using term in this application, term " electronic system " relates to the device of any type of communicating by letter with proximity transducer device 11 widely again.Electronic system 10 can comprise the device of one or more types thus, and wherein the proximity transducer device can be implemented or be coupled.The proximity transducer device can be implemented the part as electronic system 10, or utilizes the technology of any appropriate to be coupled to electronic system.As limiting examples, electronic system 10 can comprise calculation element, media player, communicator or another input unit (for example another contact-sensing apparatus or keypad) of any type thus.In some cases, electronic system 10 itself is the ancillary equipment of big system.For example, electronic system 10 can be that data input or output device, for example remote control or display unit, and it utilizes suitable wired or wireless technology and computer or medium system (for example, being used for the remote control of TV) communication.Each element (processor, memory etc.) that it shall yet further be noted that electronic system 10 may be embodied as the part of whole system, a part or its combination of contact-sensing apparatus.In addition, electronic system 10 can be proximity transducer device 11 the master or from the device.

It should be noted that, although each embodiment described herein refers to " proximity transducer device ", " contact-sensing apparatus ", " proximity transducer " or " contact mat ", but these terms used herein refer to and not only comprise conventional proximity transducer device, and comprise the equivalent device of the wide region that can detect one or more finger pieces, indicating device, contact pilotage and/or other object space.These devices can comprise, rather than be limited to touch-screen, touch pads, touch table, biologicall test identification device, person's handwriting or Symbol recognition device etc.Equally, term used herein " position " or " object space " refer to spatial-domain information for example speed, the acceleration etc. that extensively comprises absolute and relative positional information and other type, are included in the motion measurement on one or more directions.Multi-form positional information also can comprise the time history composition, as in situation of gesture identification etc.Therefore, the proximity transducer device suitably inspected object whether have and can comprise the equivalence of wide region.

Be to be further appreciated that though embodiments of the invention have been described the context of proximity transducer apparatus function here comprehensively, mechanism of the present invention also can be distributed as various forms of program products.For example, mechanism of the present invention can be implemented and distribute as the proximity transducer program on the computer-readable signal-bearing media.In addition, equally use embodiments of the invention, and no matter be used to carry out the signal-bearing media of the particular type of described distribution.The example of signal-bearing media comprises: but recording medium for example numeral and analog communication links of storage card, light and disk, hard disk and transmission medium for example.

The structure that can here propose and technically carry out various other modification and enhancings, and the basic instruction that does not break away from them.Therefore, providing many is used to detect and/or quantizes one or more system, device and processing of measuring electric capacity.Though in foregoing detailed description, proposed at least one one exemplary embodiment, should recognize, can there be numerous variations.For example, the various steps of technology described herein can be implemented by interim arbitrarily order, and are not restricted to the order that proposes and/or require here.Should be further appreciated that one exemplary embodiment described herein only is an example, and be not meant by any way and limit the scope of the invention, use or dispose.Therefore, can and arrange in the function of element and carry out various changes, and not break away from the scope of illustrating as in appended claim and legal equivalent thereof of the present invention.

Claims

1. method that is used for determining the electric capacity measured that proximity detects at transducer with a plurality of sensing electrodes and guard electrode, this method comprises:

Carry out the electric charge transfer processing, the number of execution equals at least twice, and wherein the electric charge transfer processing comprises step:

Utilize first switch that predetermined voltage is applied in a plurality of sensing electrodes at least one;

Utilize second switch that the first protection voltage is applied at least one guard electrode;

Electric charge between in shared a plurality of sensing electrodes at least one and the filter capacitor makes the electric charge of sharing accumulate on filter capacitor; With

The second protection voltage that will be different from the first protection voltage is applied to described guard electrode; With

Measure the voltage on the filter capacitor, the number of measurement equals at least once, to produce the electric capacity measured that at least one result determines that proximity detects.

2. method according to claim 1, wherein this measuring process comprises voltage and the threshold voltage on the comparison filter capacitor.

3. method according to claim 2, wherein this threshold voltage is the threshold value of many threshold value A DC.

4. method according to claim 2, wherein this threshold voltage is the threshold value of numeral input.

5. method according to claim 2, wherein this threshold voltage is the threshold value of comparator.

6. method according to claim 1 further comprises execution and the definite step that can measure the value of electric capacity of at least one result of utilizing described number.

7. method according to claim 6 comprises that further utilization can measure the value of electric capacity and obtain about object near at least one positional information in a plurality of sensing electrodes.

8. method according to claim 1, wherein the number of Ce Lianging is at least twice.

9. method according to claim 1, wherein at least one in the first protection voltage and the second protection voltage changes between the execution of electric charge transfer processing.

10. method according to claim 9, wherein at least one the term of execution variation in the first protection voltage and the second protection voltage in the electric charge transfer processing.

11. method according to claim 1 comprises further and carry out the second electric charge transfer processing that second number of execution equals at least once, wherein the second electric charge transfer processing comprises the steps:

Guide this predetermined voltage in a plurality of sensing electrodes at least one;

The 3rd protection voltage is applied at least one guard electrode;

Distributed charge between in a plurality of sensing electrodes at least one and the filter capacitor; With

The 4th protection voltage is applied at least one guard electrode.

12. method according to claim 11, wherein at least one in the third and fourth protection voltage is substantially equal to first and second one of protecting in the voltages.

13. method according to claim 12, wherein the third and fourth protection voltage is substantially equal to first and second one of protecting in the voltages.

14. method according to claim 1 wherein utilizes second switch to apply the second protection voltage.

15. method according to claim 1 wherein utilizes the 3rd switch to apply the second protection voltage.

16. method according to claim 1 wherein should be shared step and include the seedbed and connect at least one sensing electrode and filter capacitor and do not have the seedbed allow electric charge in shifting between at least one sensing electrode and filter capacitor.

17. method according to claim 1 wherein continues to apply the first protection voltage at least until at least one end that predetermined voltage is applied in a plurality of sensing electrodes.

18. method according to claim 1 is if the net charge of transferring to filter capacitor from least one guard electrode between wherein the beginning of carrying out in first time that the electric charge transfer processing is repeatedly carried out and the last measurement of repeatedly measuring finish remains on less than guard electrode on the substantially invariable voltage the net charge that is transferred.

19. method according to claim 1, wherein the first protection voltage is substantially equal to predetermined voltage.

20. method according to claim 1, wherein the first protection voltage and the difference of second protection between the voltage maximum that is not more than voltage on the charge step of once carrying out of electric charge transfer processing and the electric capacity measured between the shared step changes.

21. method according to claim 20, wherein this measuring process comprises voltage and the threshold voltage on the comparison filter capacitor, and wherein the first protection voltage and the difference of second protection between the voltage are not less than half of difference of predetermined voltage and threshold voltage.

22. method according to claim 2, wherein the first protection voltage equals predetermined voltage substantially, and the second protection voltage is one of in threshold voltage, the resetting voltage relevant with filter capacitor and the voltage between threshold voltage and the resetting voltage.

23. method according to claim 2; poor between wherein the maximum that is not more than voltage on charge step that predetermined voltage and electric charge transfer processing once carry out and the electric capacity measured between the shared step of the difference between second mean value of first mean value of the first protection voltage and the second protection voltage changes, the execution of wherein said number obtains first mean value and second mean value.

24. method according to claim 23, wherein the difference between second mean value of first mean value of the first protection voltage and the second protection voltage is not less than half that differs between predetermined voltage and the threshold voltage.

25. method according to claim 11; difference between whole second mean value of the 4th protection voltage that second voltage that first mean value that the 3rd protection voltage that the first protection voltage that the step that further comprises the voltage on the filter capacitor that resets, wherein described together number are carried out and second number are carried out is whole and described together number are carried out and second number are carried out is not more than poor between predetermined voltage and the resetting voltage relevant with filter capacitor.

26. method according to claim 1 one of wherein applies in the step of the step of predetermined voltage and shared electric charge with the step that applies the first protection voltage and one of applies in the step of the second protection voltage and carries out substantially simultaneously.

27. method according to claim 1, the step that wherein applies second guard signal begins earlier than the end of sharing step.

28. method according to claim 1 wherein applies the second protection voltage and begins beginning earlier than measuring process.

29. method according to claim 1 further comprises the step of the voltage on the filter capacitor that resets.

30. method according to claim 1, wherein the first protection voltage and the difference of second protection between the voltage be no more than predetermined voltage and described number carry out the electric charge transfer processing share step arbitrarily during at least one sensing electrode on voltage between poor.

31. one kind is disposed the digital processing unit that enforcement of rights requires 1 described method.

32. the transducer with a plurality of sensing electrodes and guard electrode is used for the electric capacity measured that definite proximity detects, wherein this transducer comprises:

Be used to carry out the device of electric charge transfer processing, the number of execution equals at least twice, and wherein this electric charge transfer processing comprises the steps:

One of share in a plurality of sensing electrodes at least and filter capacitor between electric charge, make the electric charge of sharing on filter capacitor, accumulate; With

The second protection voltage that will be different from the first protection voltage is applied at least one guard electrode; With

Be used to measure the voltage on the filter capacitor, the number of measurement equals at least once, to produce the device that at least one result determines the electric capacity measured that proximity detects.

33. a system that is used to measure electric capacity, this system comprises:

A plurality of sensing electrodes;

At least one guard electrode;

Electrical network comprises at least one filter capacitor that is coupled to these a plurality of sensing electrodes;

A plurality of sensing electrode switches, each all is coupled in a plurality of sensing electrodes at least one;

The first guard electrode switch is coupled to this at least one guard electrode; With

Controller, be coupled to each and the first guard electrode switch in a plurality of sensing electrode switches, wherein dispose this controller to carry out the electric charge transfer processing, the number of carrying out equals at least twice, and wherein this electric charge transfer processing comprises that at least one that utilize in a plurality of sensing electrode switches is applied in a plurality of sensing electrodes at least one with predetermined voltage, utilize the first guard electrode switch that the first protection voltage is applied to this at least one guard electrode, electric charge between in shared these a plurality of sensing electrodes at least one and the filter capacitor, and the second protection voltage that will be different from the first protection voltage is applied to this at least one guard electrode; Wherein further dispose this controller to measure the voltage on the filter capacitor, the number of measurement equals at least once, to produce the electric capacity measured that at least one result determines that proximity detects.

34. system according to claim 33 wherein further disposes this controller to apply the first protection voltage by a part that applies predetermined voltage at least.

35. system according to claim 33 wherein further disposes this controller and protects voltage so that the second protection voltage application begins earlier than the end of sharing step to apply second.

36. system according to claim 33, the wherein a plurality of sensing electrode switches and the first guard electrode switch comprise the signal pin of controller.

37. system according to claim 33 further comprises the passive protection network of the coupling first guard electrode switch and at least one guard electrode.

38. according to the described system of claim 37, wherein this passive protection network comprises one of capacitor and resistance.

39. according to the described system of claim 37, wherein this passive protection network comprises the impedance distributor.

40. according to the described system of claim 39; wherein this impedance distributor comprises first parts that are coupling between at least one guard electrode and first reference voltage, and is coupling in second parts between the first guard electrode switch and one of first reference voltage and second reference voltage.

41. according to the described system of claim 39; wherein this impedance distributor comprises first parts that are coupling between at least one guard electrode and first reference voltage, and second parts between one of being coupling in the second guard electrode switch and first reference voltage and second reference voltage.

42. system according to claim 33 wherein disposes this controller with by switching the first guard electrode switch between the connection of reference voltage and open-circuit condition, applies the first and second protection voltages.

43. system according to claim 33 wherein disposes this controller with by to switching the first guard electrode switch between the connection of first reference voltage and second reference voltage, applies the first and second protection voltages.

44. according to the described system of claim 43, wherein at least one in first and second reference voltages comprises supply voltage.

45. according to the described system of claim 43, wherein first reference voltage comprises first supply voltage, second reference voltage comprises the second source voltage that is different from first supply voltage.

46. according to the described system of claim 39; wherein this impedance distributor comprises first parts and second parts; wherein these first parts comprise one of the capacitor that is coupling between at least one guard electrode and first reference voltage and resistance, and wherein second parts comprise one of the capacitor that is coupling between one of the first guard electrode switch and second guard electrode switch and one of first reference voltage and second reference voltage and resistance.

47. according to the described system of claim 39, wherein this impedance distributor comprises:

Be coupled to the first node of the first guard electrode switch and at least one guard electrode; With

Be coupled to the Section Point of reference voltage.

48. according to the described system of claim 39, wherein a plurality of sensing electrodes and at least one guard electrode form the circuit of printed circuit board (PCB).

49. according to the described system of claim 39, wherein the first protection voltage comprises such voltage, selects this voltage to make near at least one the predetermined voltage that is applied to a plurality of sensing electrodes.

50. according to the described system of claim 39, wherein the second protection voltage comprises the variable voltage with time constant, selects this voltage to make near the voltage on the filter capacitor.

51. according to the described system of claim 39, wherein the second protection voltage comprises pulse code modulation signal.

52. according to the described system of claim 39, wherein the second protection voltage comprises such voltage, this voltage is near the predetermined average voltage on the filter capacitor.