JP2010191834A - Data processing system and microcomputer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data processing system which detects a change in a capacitance of a touch sensor with high accuracy by using a microcomputer. <P>SOLUTION: A voltage division node of a capacitance division circuit (CDC1) and a capacitance electrode of a touch sensor (8) are connected to an external input terminal (PG2) of a microcomputer (1) having a central processing unit (21), an analog-digital converting circuit (21), and an input buffer (101). The capacitance division circuit inputs a voltage signal obtained at the voltage division node by dividing an AC voltage to the analog-digital converting circuit via the input buffer, and the analog-digital converting circuit converts the voltage signal into digital data. At this time, the input buffer hides an input capacitance of the analog-digital converting circuit so that the input capacitance is not seen from the external input terminal. This makes the input capacitance of the analog-digital converting circuit not affect the detection accuracy of the divided voltage changed by a touch on the touch sensor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a data processing system for performing contact detection by a touch sensor using an analog / digital conversion circuit built in a microcomputer, and a microcomputer used in the data processing system.

  There is Patent Document 1 as a document describing a measurement technique for performing contact detection using a capacitive touch sensor. According to this, as shown in FIG. 12, “the switch SW1 is turned on and the capacitor Ca is charged from the power source Vcc. By turning off the switch SW1, the charge charged in the capacitor Ca is When the switches SW2 and SW3 are repeatedly turned on and off for a predetermined short time, the charge of the capacitor Ca is slowly discharged through the resistor R. The charge voltage Vx of the unknown capacitor Cx Is compared with the reference voltage Vref by the comparator Comp, and the capacitance of the unknown capacitor Cx is calculated based on the number of on / off times until it becomes smaller than the reference voltage Vref. When the capacitance is a value in the vicinity of the capacitance of the human body, it is determined that the human body is in contact. In this case, if Cx is the capacitance of the touch sensor, Vx = Cs / (Cx + Cs), and the value of Vx is lower when the human body is in contact with the touch sensor. Therefore, the number of on / off times until the discharge curve of Vx crosses the threshold voltage is less when the human body is in contact with the touch sensor. This makes it possible to detect that a human body has come into contact with the touch sensor.

JP 2006-78292 A

  Here, the change in the capacitance (Cx) when the human body comes into contact with the touch sensor is about 5 picofarads (pF) at most. Therefore, in order to detect the change as a change in Vx, it is an absolute condition that the capacitance value of Cs is not too large with respect to 5 pF, and is set to, for example, about several pF to several tens pF.

  The present inventor has studied to perform the above measurement using a microcomputer incorporating an analog / digital converter. In such a microcomputer, the analog input port of the analog / digital converter is provided with a transfer switch for constituting a plurality of analog input channels, and each transfer switch is connected to a corresponding external analog input terminal. When detection is performed by a touch sensor, the detection node of the voltage Vx is connected to an analog input terminal of the microcomputer.

  However, the analog input terminal has an input impedance. A capacitance of about several pF is always connected to the external terminal of the semiconductor integrated circuit to prevent electrostatic breakdown, and there is an input capacitance in the input stage of the other circuit. In particular, if the sample-and-hold circuit is arranged at the first stage of the analog / digital conversion circuit, the sampling capacitor appears as an input capacitor. The sampling capacity is usually about several tens of pF. In consideration of this, when the detection node of Vx is simply connected to the analog input terminal of the microcomputer, the input capacitance of the analog input terminal can be seen from the detection node, and the Cs is substantially increased. It has been found by the present inventor that the change in Vx with respect to the change in the electrostatic capacity is reduced, the detection accuracy is lowered, and there is a risk of erroneous detection.

  An object of the present invention is to provide a data processing system that can change the capacitance of a touch sensor with high accuracy using a microcomputer.

  Another object of the present invention is to provide a microcomputer suitable for detecting a change in capacitance of a touch sensor with high accuracy.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  The following is a brief description of an outline of typical inventions disclosed in the present application.

  That is, a capacitance dividing circuit is connected to a voltage dividing node and touched to an external input terminal of the input buffer of a microcomputer having a central processing unit, an analog / digital conversion circuit controlled by the central processing unit, and an input buffer. Connect the capacitive electrode of the sensor. The analog / digital conversion circuit converts the voltage signal into digital data by inputting a voltage signal obtained at the voltage dividing node when the capacitance dividing circuit divides an alternating voltage via the input buffer. At this time, the input buffer is hidden so that the input capacitance of the analog / digital conversion circuit cannot be seen from the external input terminal. That is, the input buffer has an input capacity smaller than that of the analog / digital conversion circuit. For example, an input buffer includes a gate capacitance of an input transistor as an input capacitance. As a result, the detection accuracy of the divided voltage that changes due to contact with the touch sensor does not decrease due to the influence of the input capacitance of the analog / digital conversion circuit.

  The detection of the contact of the conductor with the touch sensor is performed by forming a divided voltage with a capacitance dividing circuit including the capacitance of the touch sensor as an element thereof. Since it does not require repeated discharge, it contributes to low power consumption. In addition, an AC voltage may be supplied to the capacitance dividing circuit to generate a divided voltage, and the voltage waveform of the detection node is tracked by the residual charge when discharging is gradually repeated after charging as in Patent Document 1. Therefore, the frequency of the AC voltage may be a low speed of about several tens of kilohertz capable of capacity division, and is hard to be affected by noise, which also contributes to low power consumption. Furthermore, unlike the conventional example described in the prior art document, it is not necessary to distinguish the voltage waveform of the detection node many times while gradually discharging the charge. Therefore, the present invention detects contact with the touch sensor at high speed. can do.

  The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

  That is, the capacitance of the touch sensor can be changed with high accuracy using a microcomputer. Contact with the touch sensor can be detected at high speed.

FIG. 1 is a block diagram illustrating the main part of a data processing system according to the present invention. FIG. 2 is a block diagram illustrating the configuration of the microcomputer according to the present invention. FIG. 3 is a circuit diagram illustrating details of the output buffer and the input buffer of FIG. FIG. 4 is a flowchart illustrating a processing flow of conductor contact detection with respect to the touch sensor. FIG. 5 is a block diagram exemplifying a system configuration in the case where the microcomputer has a dedicated interface hardware for detecting a conductor contact with the touch sensor. FIG. 6 is a circuit diagram showing a specific example of the output buffer and the input buffer in FIG. FIG. 7 is a block diagram exemplifying a microcomputer in which the amplification degree of the input buffer for inputting the voltage divided by capacitance is larger than 1. FIG. 8 is a block diagram showing an example in which the AC voltage is boosted externally. FIG. 9 is a block diagram showing an example in which an AC voltage is applied to the capacitance dividing circuit from an external circuit different from the microcomputer 1. FIG. 10 is a block diagram showing an example in which a microcomputer inputs a capacitance divided voltage using an analog input port. FIG. 11 is a block diagram showing a specific example of the ADC 21. FIG. 12 is a diagram for explaining the principle of conductor contact detection in the touch sensor disclosed in Patent Document 1.

1. First, an outline of a typical embodiment of the invention disclosed in the present application will be described. Reference numerals in the drawings referred to in parentheses in the outline description of the representative embodiments merely exemplify what are included in the concept of the components to which the reference numerals are attached.

  [1] A data processing system according to a typical embodiment of the present invention includes a central processing unit, an analog / digital conversion circuit controlled by the central processing unit, a microcomputer having an input buffer, and the input buffer. A capacitance dividing circuit having a voltage dividing node connected to the external input terminal; and a touch sensor having a capacitance electrode connected to the external input terminal. The input buffer is concealed so that the input capacitance of the analog / digital conversion circuit cannot be seen from the external input terminal. The analog / digital conversion circuit converts the voltage signal into digital data by inputting a voltage signal obtained at the voltage dividing node when the capacitance dividing circuit divides an alternating voltage via the input buffer. The central processing unit detects a change in capacitance of the touch sensor based on the digital data.

  [2] In the data processing system according to item 1, the analog / digital conversion circuit samples the input voltage with a sample-and-hold circuit, generates a reference voltage with a capacitance array type local digital / analog conversion circuit, The reference voltage is compared by a comparator, a conversion bit is determined for each successive bit from the most significant bit according to the comparison result, and a reference voltage for determining the next lower bit is generated according to the comparison result. It is a successive approximation type analog-digital conversion circuit by distribution.

  [3] In the data processing system according to item 1, the input buffer includes a gate capacitance of an input transistor receiving an input from the external input terminal as an input capacitance.

  [4] In the data processing system according to item 1, the capacitor dividing circuit includes a first capacitor element (2, 4, 6) in which the AC voltage is applied to one capacitor electrode and the voltage dividing node is connected to the other capacitor electrode. ) And a parasitic capacitance component (3, 5, 7) connected to the voltage dividing node.

  [5] In the data processing system according to item 1, the macro computer further includes an output buffer for outputting the AC voltage. The program control by the CPU or the dedicated logic circuit (125) makes it possible to easily synchronize the conversion operation by the analog / digital conversion circuit and the output operation of the AC voltage.

  [6] In the data processing system according to item 5, the central processing unit outputs the AC voltage by alternately outputting a high level and a low level from the output buffer at a predetermined cycle. The AC voltage can be easily output by program control by the CPU.

  [7] In the data processing system according to item 5, the microcomputer has a pulse width modulation circuit (29), and the output buffer uses a square pulse voltage having a pulse width generated by the pulse width modulation circuit as the AC voltage. Output. The AC voltage can be more easily output by program control by the CPU.

  [8] In the data processing system according to item 6, the analog / digital conversion circuit converts the voltage signal into digital data in synchronization with a high level output operation of the output buffer.

  [9] In the data processing system according to item 8, the microcomputer determines that the conductor is in contact with the touch sensor when the digital data changes beyond a threshold value.

  [10] In the data processing system according to item 9, the microcomputer periodically calibrates the threshold value. When the capacitance value of the capacitance dividing circuit and the input capacitance of the input buffer vary due to an atmosphere such as temperature and humidity, manufacturing variations, and the like, the detection accuracy can be maintained.

  [11] In the data processing system according to item 5, the microcomputer further includes an analog input port. The input buffer and the output buffer are included in a general-purpose port. The general-purpose port has a first selector that selects which of the output of the input buffer is supplied to the analog / digital conversion circuit or other circuits. The analog port includes: a second selector that selects which of a plurality of analog input terminals is to be conducted to a subsequent stage; and a signal selected by the first selector or a signal selected by the second selector is the analog selector. A third selector that selects whether to supply to the digital conversion circuit. As a result, the input buffer of the general-purpose port can be used as the input buffer of the analog / digital conversion circuit. Therefore, it is not necessary to add an analog port having a special input buffer. Analog ports that receive normal analog-to-digital conversion inputs are generally equipped with a selector switch for selecting an analog input channel, no input buffer is provided, and changes in analog values due to the input buffer are generally suppressed. is there.

  [12] In the data processing system according to item 1, the input buffer is an amplifier having an amplification factor greater than one. Since the accuracy of the analog value itself does not have to be a serious problem, it is possible to amplify the input data and further facilitate contact detection to the touch sensor.

  [13] In the data processing system according to item 1, a low-pass filter is disposed between the amplifier and the analog / digital conversion circuit. Since the high frequency noise that becomes relatively large can be reduced by increasing the amplification degree, it is possible to improve the accuracy of detecting a change in the divided voltage.

  [14] <Multiple channelization> A data processing system according to another aspect of the present invention includes a central processing unit, an analog / digital conversion circuit controlled by the central processing unit, a plurality of input buffers, and a plurality of input buffers. A microcomputer having a selector for selecting an output to be supplied to the analog / digital conversion circuit; a plurality of capacitance dividing circuits each having a voltage dividing node individually connected to an external input terminal of each of the input buffers; And a plurality of touch sensors having capacitance electrodes individually connected to the external input terminals. Each of the input buffers is hidden so that the input capacitance of the analog / digital conversion circuit cannot be seen from the corresponding external input terminal. The analog / digital conversion circuit converts the voltage signal into digital data by inputting the voltage signal obtained at the voltage dividing node when the capacitance dividing circuit divides the alternating voltage through the input buffer. The central processing unit detects a change in capacitance of the touch sensor based on the digital data. The same field effect as described above can also be obtained when multi-channel detection of conductor contact to the touch sensor is performed.

  [15] In the data processing system according to item 14, the microcomputer has a register for storing control data for controlling selection of the selector, and the central processing unit can access the register. The multi-channel detection of the conductor contact detection to the touch sensor can be easily controlled by the program control of the central processing unit.

  [16] In the data processing system according to item 14, the input buffer includes a gate capacitance of an input transistor receiving an input from the external input terminal as an input capacitance.

  [17] A data processing system according to still another aspect of the present invention includes a central processing unit, an analog / digital conversion circuit controlled by the central processing unit, a microcomputer having an input buffer, and an external input terminal of the input buffer. And a touch sensor in which a capacitive electrode is connected to the external input terminal. The input buffer has an input capacitance smaller than a capacitance connected downstream of the voltage dividing node of the capacitance dividing circuit outside the external input terminal. The analog / digital conversion circuit converts the voltage signal into digital data by inputting the voltage signal obtained at the voltage dividing node when the capacitance dividing circuit divides the alternating voltage through the input buffer. The central processing unit detects a change in capacitance of the touch sensor based on the digital data. Item 1 differs from item 1 in the way of setting the input impedance of the input buffer, and has the same effect as described above.

  [18] A data processing system according to still another aspect of the present invention includes a central processing unit, an analog / digital conversion circuit controlled by the central processing unit, a microcomputer having an input buffer, and an external input terminal of the input buffer. And a touch sensor in which a capacitive electrode is connected to the external input terminal. The input buffer has an input capacitance smaller than that of the analog / digital conversion circuit. The analog / digital conversion circuit converts the voltage signal into digital data by inputting the voltage signal obtained at the voltage dividing node when the capacitance dividing circuit divides the alternating voltage through the input buffer. The central processing unit detects a change in capacitance of the touch sensor based on the digital data. Data processing system. Item 1 differs from item 1 in the way of setting the input impedance of the input buffer, and has the same effect as described above.

  [19] In the data processing system according to item 18, the analog-to-digital conversion circuit samples the input voltage with a sample-and-hold circuit, generates a reference voltage with a capacitor array type local digital-to-analog conversion circuit, The reference voltage is compared by a comparator, a conversion bit is determined for each successive bit from the most significant bit according to the comparison result, and a reference voltage for determining the next lower bit is generated according to the comparison result. It is a successive approximation type analog-digital conversion circuit by distribution.

  [20] In the data processing system according to item 18, the input buffer has a gate capacitance of an input transistor receiving an input from the external input terminal as the input capacitance.

  [21] A microcomputer according to the present invention includes a central processing unit, an analog / digital conversion circuit controlled by the central processing unit, a general-purpose port, an analog port, and a register, and is formed as a semiconductor integrated circuit. The general-purpose port has an output buffer and an input buffer. The general-purpose port (23) has a first selector (104 to 106) for selecting whether the output of the input buffer is supplied to the analog / digital conversion circuit or another circuit. The input buffer includes a gate capacitance of an input transistor that receives an input from the external input terminal as an input capacitance. The analog port (22) is selected by the second selector (115) for selecting which of the plurality of analog input terminals is to be conducted to the subsequent stage, and the signal selected by the first selector or the second selector And a third selector (113) for selecting which of the signals is supplied to the analog / digital conversion circuit. The register stores control data for controlling selection of the first selector, the second selector, and the third selector. The central processing unit can access the register. A microcomputer suitable for the data processing method can be obtained.

  [22] In the microcomputer according to item 21, the analog / digital conversion circuit samples an input voltage by a sample-and-hold circuit, generates a reference voltage by a capacitance array type local digital / analog conversion circuit, and the input voltage and the reference Charge redistribution that compares the voltage with a comparator, determines conversion bits for each bit sequentially from the most significant bit according to the comparison result, and generates a reference voltage for the next lower bit determination according to the comparison result Is a successive approximation type analog-digital conversion circuit.

2. Details of Embodiments Embodiments will be further described in detail.

  FIG. 2 schematically shows the configuration of the microcomputer according to the present invention. A microcomputer (MCU) 1 shown in the figure is formed on a single semiconductor substrate such as single crystal silicon by a complementary MOS integrated circuit manufacturing technique or the like.

  The microcomputer 1 includes a central processing unit (CPU) 20, a RAM 25 as a work area of the CPU 20, a non-volatile memory (ROM) 26 for storing programs executed by the CPU 20, parameter data used by the CPU 20 for executing the programs, An interrupt controller (INTC) 27 that gives an interrupt to the CPU 20 in response to an interrupt request from a peripheral circuit and a peripheral circuit are provided, and the internal bus 31 is shared. As peripheral circuits, a clock pulse generator (CPG) 30 that generates a synchronous clock signal inside the microcomputer 1, a timer counter (TMR) 28, a pulse width modulation circuit (PWM) 29, an analog / digital conversion circuit (ADC) 21, an analog A port (APRT) 22 and general-purpose ports (GPRT) 23 and 24 are provided. The CPG 30 generates self-excited oscillation in a vibrator (not shown) coupled to clock terminals EXTAL and XTAL or generates an internal synchronous clock signal based on a system clock signal (not shown) supplied from the terminal. External analog input terminals PA1 to PAn are connected to APRT22. The general-purpose ports 23 and 24 are connected to external general-purpose terminals PG1 to PGm and PGn to PGx used for data input / output, address output, and other signal input / output. As will be described in detail later, the ADC 21 is supplied with an analog signal output from the APRT 22 or an analog signal output from the GPRT 23. In FIG. 2, a two-dot chain line leading to the ADC 21 conceptually indicates an analog signal input path.

  FIG. 1 illustrates a main part of a data processing system for detecting a conductor contact of a touch sensor using the microcomputer 1 of FIG. 2 as a data processing system according to the present invention.

  8, 9, and 10 are touch sensors. The touch sensor has a capacitive electrode, and when a conductor such as a human body comes into contact with the capacitive electrode via a dielectric, the capacitance increases. This change is detected by using the capacity dividing circuit and the microcomputer 1.

  The CDC1 is a capacitance dividing circuit configured by capacitors 2 and 3 connected in series with the voltage dividing node DN1 interposed therebetween, and the capacitance electrode of the touch sensor 8 is coupled to the voltage dividing node DN1. The CDC2 is a capacitance dividing circuit configured by capacitors 4 and 5 connected in series with the voltage dividing node DN2 interposed therebetween, and the capacitance electrode of the touch sensor 9 is coupled to the voltage dividing node DN2. The CDC3 is a capacitance dividing circuit configured by capacitors 6 and 7 connected in series with the voltage dividing node DN1 interposed therebetween, and the capacitance electrode of the touch sensor 10 is coupled to the voltage dividing node DN3.

  One end of each capacitance dividing circuit CDC1, CDC2, CDC3 is commonly connected to the external output terminal PG1, and the voltage dividing nodes DN1, DN2, DN3 are individually connected to the external output terminals PG2, PG2, PG4. Is an alternating voltage from the output buffer 100, for example, a square pulse voltage is applied at a low frequency. The other ends of the respective capacitance dividing circuits CDC1, CDC2, CDC3 are coupled to a circuit ground voltage (ground voltage) Vss.

  The general-purpose port 23 includes an output buffer 100 and input buffers 101 to 103 that are representatively shown. Although the output buffer 100 is not particularly limited, the output buffer 100 is configured by a push-pull circuit such as a CMOS. The input buffers 101 to 103 are configured with a source follower circuit although not particularly limited. The output buffer 100 and the input buffers 101 to 103 are connected to a port data register (not shown), and the output buffer 100 outputs the data latched in the port data register from the bus 31 through this, and the input buffers 101 to 103 are output. The data latched in the port data register is supplied to the bus 31. In particular, the general-purpose port 23 includes output selection circuits (OSL) 104, 105, and 106 that select whether the output of the input buffers 101 to 103 is supplied to the port data register in the subsequent stage or supplied to the ADC 21. In short, a path for supplying analog input to the ADC 321 via the input buffer circuit of the general-purpose port 23 can be selected. It is not necessary to arrange a dedicated input buffer in the analog port for analog input. In response to this, the analog port 22 that can selectively use a plurality of analog input channels receives an input signal from the selected analog input channel or a signal selected by the output selectors 104 to 106 from the general-purpose port 23. An input selector (ISL) 113 for selection is provided. Selection of the analog channel, that is, selection of the external analog input terminals PA1, PA2, and PA3 is performed by an input selector 115 including transfer switches (TR) 110, 11, and 112. The selection control data for determining the selection state by the selectors 104 to 106 is not particularly limited, but is set in the register (GPREG) 32 by the CPU 20. The selection control data for determining the selection state by the selectors 113 and 115 is not particularly limited, but is set in the register (APREG) 33 by the CPU 20.

  The analog input terminal of the ADC 21 is coupled to the output of the selector 113. In FIG. 1, reference numeral 35 explicitly indicates an input capacitor including a sampling capacitor included in the sample hold circuit of the ADC 21.

  FIG. 3 shows details of the output buffer 100 and the input buffers 104 to 106 in FIG. Reference numerals 100A and 100B schematically represent push-pull transistors of the output buffer 100. Reference numerals 101A, 102A, and 103A denote N-channel MOS transistors when the input buffers 104 to 106 are configured as source follower circuits, and reference numerals 101B, 102B, and 103B denote resistance elements.

  A specific example of the ADC 21 is shown in FIG. Although not particularly limited, the ADC 21 is configured as a successive approximation type analog-digital conversion circuit by charge redistribution, and includes a sample hold circuit (S / H) 200, a comparator 201, a successive approximation register (SAREG) 202, a local digital / analog. A conversion circuit (LCLDAC) 203, a reference voltage generation circuit (VREFG) 204, an output register (OTREG) 205, and a control circuit (CONT) 206 are provided. The clock signal CLK is supplied to the control circuit 206 and the sample hold circuit 200, and an analog / digital conversion operation is performed in synchronization with the clock signal CLK. The LCLDAC 203 includes a binary weighted capacitor array and performs digital-to-analog conversion by analog redistribution.

  The input voltage Vin is sampled by a sample hold circuit (S / H) 200, a reference voltage is generated by a local digital / analog converter circuit 201, the input voltage and the reference voltage are compared by a comparator 201, and the comparison result is obtained. A conversion bit is determined for each successive bit from the most significant bit, and a reference voltage for determining the next lower bit is generated according to the comparison result, that is, the input voltage Vin is sampled and held, and the full-case voltage is obtained by the LCLDAC 203 A voltage (1 / 2FS) that is half of (FS) is generated, and the comparator 201 determines whether the input voltage is larger than half of the full-case voltage. Set to the most significant bit. Next, when the previous determination is “1”, a voltage of (1/2 + 1/4) FS is generated by the LCLDAC 203 and compared with the input voltage Vin when it is “0”. Similarly, the value of the second bit is determined to be “1” or “0”. Such an operation is repeated until the value of the least significant bit is determined, and finally, digital data 205 is obtained as a conversion result in the output register 205.

  In FIG. 1 and FIG. 3, the input capacity of the input buffers 101, 102, 103 is smaller than the input capacity of the ADC 21, that is, the capacity of the input stage including the sampling capacity 35. For example, the value of the sampling capacitance is about 20-30 pF. In the case of a source follower circuit, the input capacitance of the source follower MOS transistors 101A, 102A, 103A of the input buffers 101, 102, 103 is extremely small. If the capacitance when the person touches the touch sensors 8, 9, 10 is about 5 pF, the capacitors 3, 5, 7 may be set to a small capacitance value of 5 pF or less, for example. A capacitance value of about several tens of pF, which is not too large with respect to 5 pF, may be set for 4 and 6. For example, when a capacitance element of 20 pF is adopted for the capacitors 2, 4 and 6, and a capacitance value of several pF is adopted for the capacitors 3, 5, and 7 according to this, even if no capacitance element is provided, the partial pressure is reduced. It can be covered by the parasitic capacitances of the nodes DN1, DN2 and DN3. The parasitic capacitance is a parasitic capacitance of wiring connected to the voltage dividing nodes DN1, DN2, and DN3, and an electrostatic breakdown preventing capacitance (several pF) provided on the external terminals PG2, PG3, and PG4 on the microcomputer 1 chip. .

  FIG. 4 illustrates a processing flow of conductor contact detection for the touch sensor. When the touch sensor to be detected is switched every predetermined time. For example, when channel 1 of the touch sensor 8 is to be measured, the terminal PG1 is driven to a high level (S1), and the value of the voltage dividing node DN1 is thereby set to the terminal. Input from PG2 via the input buffer 101 (S2), and the ADC 21 inputs the input voltage to perform an analog-digital conversion operation (S3). The terminal PG1 is driven to a low level at an appropriate timing thereafter (S4). The operation is waited for a certain period of time so that the frequency of the square pulse output operation by the output buffer 100 is performed at a predetermined cycle such as 50 kHz (S5), and it is determined whether the operation has been performed a plurality of times, for example, four times (S6). ) The above operation is repeated until four times. By repeating the measurement of the same channel a plurality of times, the CPU 20 performs averaging or the like on the plurality of analog / digital conversion results so as not to be affected by the measurement error. The process of FIG. 4 is sequentially performed while sequentially switching the touch sensors to be measured, and thereby, the conductor contact with the touch sensor can be detected asynchronously.

  The CPU 20 compares the conversion result with a threshold value, and determines that it is non-contact if it is larger than the threshold value, and is contact if it is smaller than the threshold value. The CPU 20 periodically calibrates the threshold value. This is to maintain detection accuracy when the capacitance value of the capacitance dividing circuit and the input capacitance of the input buffer vary due to an atmosphere such as temperature and humidity, manufacturing variations, and the like.

  The data processing system has the following operational effects.

  (1) The input buffers 101 to 103 hide the input capacitance of the analog / digital conversion circuit 21 from the external input terminals PG2, PG3, and PG4. That is, the input buffer uses the gate capacitance of the input MOS transistors 101A, 102A, and 103A as the input capacitance. As a result, the detection accuracy of the divided voltage that changes when the conductor touches the touch sensors 8, 9, 10 based on the divided voltage of the capacitance dividing circuits CDC 1, CDC 2, CDC 3 is the input capacitance of the analog / digital conversion circuit 21. It can suppress that it falls under the influence of 35.

  (2) For detecting the conductor contact with the touch sensors 8, 9, and 10, a divided voltage is formed by the capacitance dividing circuits CDC1, CDC2, and CDC3 including the capacitance of the touch sensors 8, 9, and 10 as elements thereof. As described in Patent Document 1, it is not necessary to repeat charging / discharging with respect to the charging capacity, which contributes to low power consumption. In addition, an AC voltage may be supplied to the capacitance dividing circuit to generate a divided voltage, and the voltage waveform of the detection node is tracked by the residual charge when discharging is gradually repeated after charging as in Patent Document 1. Therefore, the frequency of the AC voltage may be a low speed of about several tens of kilohertz capable of capacity division, and is hard to be affected by noise, which also contributes to low power consumption.

  (3) Since it is not necessary to distinguish the voltage waveform of the detection node many times while gradually discharging the charge as in the conventional example, the present invention can detect contact with the touch sensor at high speed.

  (4) By outputting a square pulse voltage at a predetermined frequency from the output buffer 100, the CPU 20 can easily form an alternating voltage for the capacity division by program control by the CPU 20.

  (5) By providing the general-purpose port 23 with the selectors 104 to 106 and the analog port 22 with the selector 113, the input buffers 1021, 102, 103 of the general-purpose port 23 can be used as the input buffer of the analog-digital conversion circuit 21. Can do. Therefore, it is not necessary to add an analog port having a special input buffer. An analog port that receives a normal analog / digital conversion input is provided with a selector 115 including a selection switch for selecting an analog input channel, no input buffer is provided, and changes in analog values due to the input buffer are suppressed. This is because it is common.

  FIG. 5 illustrates a system configuration in the case where the microcomputer includes dedicated interface hardware for detecting the contact of the conductor with respect to the touch sensor. FIG. 6 shows a specific example of the output buffer and the input buffer in FIG. In the figure, reference numeral 40 denotes a dedicated interface circuit for detecting contact of a conductor with respect to the touch sensor, and is built in the microcomputer 1A. The interface circuit 40 includes an output buffer 120 that outputs a square pulse voltage, and an input buffer (IBUF) 121 that is connected to the voltage dividing node DN1. 120A and 120B denote push-pull transistors, and 121A denotes an N-channel source follower MOS transistor. A logic circuit 125 outputs a square pulse signal at a predetermined frequency from the output buffer according to the detection timing of the touch sensor. An external output terminal PS1 is assigned exclusively to the output buffer 120, and an external input terminal PD2 is assigned exclusively to the input buffer 121. If the interface circuit is dedicated and low flow is eliminated, the same effects as in Fig. 1 and Fig. 3 are achieved.

  FIG. 7 shows an example of a microcomputer 1B in which the amplification degree of an input buffer for inputting a voltage divided by capacitance is larger than one. The input buffer 130 is configured by an amplifier having an amplification degree greater than 1. A low pass filter 131 is arranged at the next stage. In the conductor contact detection of the touch sensor, the accuracy of the analog value itself does not have to be a serious problem. Therefore, it is possible to amplify the input data and further facilitate the contact detection to the touch sensor. By providing a low-pass filter, high-frequency noise that becomes relatively large due to amplification by the amplifier can be reduced, so that the accuracy of detecting a change in the divided voltage can be improved.

  FIG. 8 shows an example in which the AC voltage is boosted externally. The output voltage of the output buffer 100 is set to a boost DC-DC power supply configuration, and a voltage equal to or higher than the power supply voltage Vdd is applied to the capacity dividing circuit CDC1 to set the voltage of the capacity flight pressure node DN1 high. Thereby, the voltage change obtained by the conductor contact to a touch sensor can be enlarged, and detection accuracy can be improved.

  FIG. 9 shows an example in which an AC voltage is applied to the capacitance dividing circuit from an external circuit different from the microcomputer 1. The external circuit 150 supplies a square pulse voltage having a predetermined frequency to the capacitance dividing circuit CDC1.

  FIG. 10 shows an example in which the microcomputer 1C inputs a capacitance divided voltage using an analog input port (APRT) 167. Reference numerals 160 and 161 output square pulse voltages at a predetermined frequency. Reference numerals 162 and 163 denote buffer circuits having an input capacity smaller than the sampling capacity of the ADC, and are constituted by a source follower circuit, a voltage follower circuit, and the like.

  Although the invention made by the present inventor has been specifically described based on the embodiments, it is needless to say that the present invention is not limited thereto and can be variously modified without departing from the gist thereof.

  For example, the type of circuit module built in the microcomputer and the configuration of the bus connection are not limited to those shown in FIG. The input buffer is not limited to a source follower circuit, and an appropriate circuit configuration such as a voltage follower circuit or a CMOS inverter can be employed.

  A single-chip microcomputer and a plurality of capacity dividing circuits can be mounted on one module. At this time, the touch sensor may be connected to the external terminal of the module.

  The frequency of the AC voltage applied to the capacitance dividing circuit is not limited to about several tens of kHz, and may be any frequency that allows capacitive voltage division.

  A plurality of touch sensors may be arranged in a matrix. In the example of FIGS. 1 and 3, the number of input channels of the touch sensor is three, but the number is not limited to this, and the number of channels can be appropriately increased or decreased.

1 Microcomputer (MCU)
20 Central processing unit (CPU)
25 RAM
26 Nonvolatile memory (ROM)
27 Interrupt controller (INTC)
31 Internal bus 30 Clock pulse generator (CPG)
28 Timer Counter (TMR)
29 Pulse width modulation circuit (PWM)
21 Analog-digital converter (ADC)
22 Analog port (APRT)
23, 24 General-purpose port (GPRT)
PA1 to PAn External analog input terminals PG1 to PGm, PGn to PGx External general purpose terminals 8, 9, 10 Touch sensor CDC1, CDC2, CDC3 Capacitance dividing circuit DN1, DN2, DN3 Voltage dividing nodes 2, 3, 4, 5, 6, 7 Capacity 100 Output buffer 101-103 Input buffer 104, 105, 106 Output selector (OSL)
113 Input selector (ISL)

Claims (22)

A central processing unit, an analog / digital conversion circuit controlled by the central processing unit, and a microcomputer having an input buffer;
A capacitance dividing circuit having a voltage dividing node connected to an external input terminal of the input buffer;
A touch sensor having a capacitor electrode connected to the external input terminal,
The input buffer is concealed so that the input capacitance of the analog / digital conversion circuit cannot be seen from the external input terminal,
The analog-digital conversion circuit inputs a voltage signal obtained at the voltage dividing node by dividing the AC voltage by the capacitance dividing circuit via the input buffer, and converts the voltage signal into digital data.
The data processing system, wherein the central processing unit detects a change in capacitance of a touch sensor based on the digital data.   The analog / digital conversion circuit samples the input voltage with a sample and hold circuit, generates a reference voltage with a capacitance array type local digital / analog conversion circuit, compares the input voltage with the reference voltage with a comparator, and compares A sequential comparison type analog-to-digital converter using charge redistribution that determines the conversion bit for each sequential bit from the most significant bit according to the result and generates a reference voltage for the next lower bit determination according to the comparison result. 2. The data processing system according to claim 1, wherein:   The data processing system according to claim 1, wherein the input buffer includes a gate capacitance of an input transistor that receives an input from the external input terminal as an input capacitance.   The capacitance dividing circuit includes a first capacitance element in which the AC voltage is applied to one capacitance electrode and the voltage dividing node is connected to the other capacitance electrode, and a series circuit of a parasitic capacitance component connected to the voltage dividing node. The data processing system according to claim 1.   The data processing system according to claim 1, wherein the macro computer further includes an output buffer that outputs the AC voltage.   6. The data processing system according to claim 5, wherein the central processing unit outputs the AC voltage by alternately outputting a high level and a low level from the output buffer at a predetermined cycle.   6. The data processing system according to claim 5, wherein the microcomputer has a pulse width modulation circuit, and the output buffer outputs a square pulse voltage having a pulse width generated by the pulse width modulation circuit as the AC voltage.   7. The data processing system according to claim 6, wherein the analog / digital conversion circuit converts the voltage signal into digital data in synchronization with a high level output operation of the output buffer.   The data processing system according to claim 8, wherein the microcomputer determines that the conductor is in contact with the touch sensor based on whether the digital data exceeds a threshold value.   The data processing system according to claim 9, wherein the microcomputer periodically calibrates the threshold value. The microcomputer has an analog input port;
The input buffer and the output buffer are included in a general-purpose port;
The general-purpose port has a first selector for selecting which of the output of the input buffer is supplied to the analog / digital conversion circuit or other circuit;
The analog port includes a second selector that selects which of a plurality of analog input terminals is to be conducted to a subsequent stage, and a signal selected by the first selector or a signal selected by the second selector as the analog port. 6. A data processing system according to claim 5, further comprising a third selector for selecting whether to supply to the digital conversion circuit.   The data processing system according to claim 1, wherein the input buffer is an amplifier having an amplification factor greater than one.   The data processing system according to claim 1, wherein a low-pass filter is disposed between the amplifier and the analog / digital conversion circuit. A microcomputer having a central processing unit, an analog / digital conversion circuit controlled by the central processing unit, a plurality of input buffers, and a selector for selecting an output of the plurality of input buffers and supplying the selected output to the analog / digital conversion circuit; ,
A plurality of capacitance dividing circuits in which voltage dividing nodes are individually connected to external input terminals of the respective input buffers;
A plurality of touch sensors in which capacitive electrodes are individually connected to each of the external input terminals, and
Each of the input buffers is concealed so that the input capacitance of the analog / digital conversion circuit cannot be seen from the corresponding external input terminal,
The analog-digital conversion circuit converts the voltage signal into digital data by inputting the voltage signal obtained at the voltage dividing node by dividing the AC voltage by the capacitance dividing circuit via the input buffer,
The data processing system, wherein the central processing unit detects a change in capacitance of a touch sensor based on the digital data. The microcomputer has a register for storing control data for controlling selection of the selector,
The data processing system of claim 14, wherein the central processing unit is accessible to the register.   The data processing system according to claim 14, wherein the input buffer includes a gate capacitance of an input transistor that receives an input from the external input terminal as an input capacitance. A central processing unit, an analog / digital conversion circuit controlled by the central processing unit, and a microcomputer having an input buffer;
A capacitance dividing circuit having a voltage dividing node connected to an external input terminal of the input buffer;
A touch sensor having a capacitor electrode connected to the external input terminal,
The input buffer has an input capacitance smaller than a capacitance connected downstream of the voltage dividing node of the capacitance dividing circuit outside the external input terminal;
The analog-digital conversion circuit converts the voltage signal into digital data by inputting the voltage signal obtained at the voltage dividing node by dividing the AC voltage by the capacitance dividing circuit via the input buffer,
The data processing system, wherein the central processing unit detects a change in capacitance of a touch sensor based on the digital data. A central processing unit, an analog / digital conversion circuit controlled by the central processing unit, and a microcomputer having an input buffer;
A capacitance dividing circuit having a voltage dividing node connected to an external input terminal of the input buffer;
A touch sensor having a capacitor electrode connected to the external input terminal,
The input buffer has an input capacity smaller than the input capacity of the analog-digital conversion circuit;
The analog-digital conversion circuit converts the voltage signal into digital data by inputting the voltage signal obtained at the voltage dividing node by dividing the AC voltage by the capacitance dividing circuit via the input buffer,
The data processing system, wherein the central processing unit detects a change in capacitance of a touch sensor based on the digital data.   The analog / digital conversion circuit samples the input voltage with a sample and hold circuit, generates a reference voltage with a capacitance array type local digital / analog conversion circuit, compares the input voltage with the reference voltage with a comparator, and compares A sequential comparison type analog-to-digital converter using charge redistribution that determines the conversion bit for each sequential bit from the most significant bit according to the result and generates a reference voltage for the next lower bit determination according to the comparison result. The data processing system of claim 18, wherein:   The data processing system according to claim 18, wherein the input buffer has a gate capacitance of an input transistor that receives an input from the external input terminal as the input capacitance. A central processing unit, an analog-digital conversion circuit controlled by the central processing unit, a general-purpose port, an analog port, and a register;
The general-purpose port has an output buffer and an input buffer,
The general-purpose port has a first selector that selects whether the output of the input buffer is supplied to the analog-digital conversion circuit or another circuit;
The input buffer includes, as an input capacitance, a gate capacitance of an input transistor that receives an input from the external input terminal,
The analog port includes a second selector that selects which of a plurality of analog input terminals is to be conducted to a subsequent stage, and a signal selected by the first selector or a signal selected by the second selector as the analog port. A third selector for selecting whether to supply to the digital conversion circuit;
The register stores control data for controlling selection of the first selector, the second selector, and the third selector;
The central processing unit is accessible to the register;
A microcomputer integrated into a semiconductor integrated circuit.   The analog / digital conversion circuit samples the input voltage with a sample and hold circuit, generates a reference voltage with a capacitance array type local digital / analog conversion circuit, compares the input voltage with the reference voltage with a comparator, and compares A sequential comparison type analog-to-digital converter using charge redistribution that determines the conversion bit for each sequential bit from the most significant bit according to the result and generates a reference voltage for the next lower bit determination according to the comparison result. The microcomputer according to claim 21, wherein

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