TWI712937B - Capacitance detection circuit and operation method the same - Google Patents

Abstract

An exemplary embodiment of the present disclosure illustrates a capacitance detection circuit and operation method the same for adjusting a capacitance of a variable capacitor in an adapted capacitance mode and detecting a capacitance change of a sensing capacitor in a touch button mode. The capacitance detection circuit is to integrate a storage capacitor into a single chip to avoid the misjudgment of detection caused by changes in ambient temperature and humidity, and to adjust the capacitance value of the variable capacitor in the adapted capacitance mode, so that the touch value of each touch button on the counter can be consistent.

Description

Capacitance detection circuit and its operation method

The invention relates to a capacitance detection circuit and an operation method thereof, and more particularly to a capacitance detection circuit and an operation method thereof that can be integrated into a single chip and achieve higher detection resolution.

Capacitive touch has become a necessary function of today's products, and the capacitive touch device uses a capacitance detection circuit to detect the finger capacitance formed between the conductor (for example, copper sheet) used as the button and the user's finger. For example, please refer to FIG. 1, which is a schematic diagram of a conventional capacitance detection circuit. The capacitance detection circuit 10 can be integrated in a single chip, and it is coupled to a microcontroller (not shown in FIG. 1) and at least one conductor used as a button, and a storage capacitor Cs is connected externally. To facilitate the following description, the capacitance detection circuit 10 of FIG. 1 only uses an example of coupling one conductor 12, and the capacitance detection circuit 10 includes a switch SW1, a switch SW2, a switch SW3, and a voltage detector 101.

Specifically, the capacitance detection circuit 10 is coupled to the conductor 12 through the node A, and the switch SW1 is coupled between the node A and the storage capacitor Cs. The switch SW2 is coupled between the node A and the power supply voltage VDD, the switch SW3 is coupled between the ground voltage GND and the storage capacitor Cs, and the switch SW3 and the switch SW1 are jointly coupled to the first end of the storage capacitor Cs through the node B, the storage capacitor The second terminal of Cs is coupled to the ground voltage GND. In addition, the voltage detector 101 is implemented by a comparator CP, and the non-inverting input terminal of the comparator CP is also coupled to the node B, and the inverting input terminal receives the reference voltage Vref.

As shown in Figure 1, in addition to the finger capacitance Cf, the inductive capacitance outside the chip also has a parasitic capacitance Cd mainly derived from the Printed Circuit Board (PCB), and the operation method of the capacitance detection circuit 10 is to conduct first The switch SW3 provides a discharge path to discharge the voltage Vcs of the storage capacitor Cs to a zero ground voltage GND. Secondly, the switch SW3 is turned off and the switch SW2 is turned on, so that a charging path is provided to charge the parasitic capacitance Cd and the voltage Vdf of the finger capacitance Cf to the power supply voltage VDD.

Next, switch SW2 is turned off and switch SW1 is turned on, so as to provide a charge transfer path to transfer the charge stored in parasitic capacitance Cd and finger capacitance Cf to storage capacitance Cs, and then repeatedly charge parasitic capacitance Cd and finger capacitance Cf, and The stored charge is transferred to the storage capacitor Cs, or the switch SW2 and the switch SW1 are turned on cyclically, until the voltage Vcs of the storage capacitor Cs reaches the reference voltage Vref. In this process, if the parasitic capacitance Cd and the finger capacitance Cf are larger, the more charge is transferred to the storage capacitor Cs each time the switch SW1 is turned on, and the number of cycles required to turn on the switch SW2 and SW1 is less .

However, because the finger capacitance Cf when the finger 11 does not press the conductor 12 is zero, but the finger capacitance Cf when the conductor 12 is pressed is about 0.5pF, so that the microcontroller can judge the finger based on the number of cycles of turning on the switch SW2 and SW1 11 Whether there is a pressing conductor 12. In other words, if the capacitance value of the parasitic capacitance Cd is larger, the capacitance change amount of the finger capacitance Cf that can be detected by the capacitance detection circuit 10 is smaller. In addition, as the position of each touch button (ie each conductor) is different, the PCB wiring method and length are also different, and the wiring is easily affected by the grounding terminal, making the capacitance value of the parasitic capacitance Cd in each touch The buttons are all inconsistent, so the PCB design on the capacitive touch device becomes very difficult.

On the other hand, because the storage capacitor Cs is usually greater than 3000 pF, it cannot be integrated with the capacitance detection circuit 10 in a single chip, and it is difficult to achieve high resolution except for the comparator CP used to compare the voltage Vcs and the reference voltage Vref. , The storage capacitor Cs is also easily affected by changes in ambient temperature and humidity due to its external connection, causing false detections. In addition, capacitive touch buttons are also susceptible to interference from external signals, such as radio frequency interference, radiation interference, and power noise interference. Therefore, how to design a capacitance detection circuit that can be integrated on a single chip and achieve higher detection resolution has become an important issue in this field.

In view of this, an embodiment of the present invention provides a capacitance detection circuit, which is coupled to a conductor and includes a storage capacitor and a variable capacitor. The capacitance detection circuit is used to adjust the capacitance value of the variable capacitor in the adaptive capacitance mode, and to detect the change in the capacitance value of the sensing capacitor in the touch button mode to generate a touch value related to the conductor. In the adaptive capacitance mode, the capacitance detection circuit is used to perform: Step A, providing a first charging path to charge the voltage of the sensing capacitor to the first power supply voltage, and providing a second charging path to charge the voltage of the storage capacitor to The second power supply voltage, wherein the second power supply voltage is less than the first power supply voltage, and the sensing capacitor includes parasitic capacitance and finger capacitance; step B, providing a discharge path to discharge the voltage of the variable capacitor to the ground voltage, and providing a first charge transfer path The charge stored in the sensing capacitor is transferred to the storage capacitor; step C, a first charging path is provided to charge the voltage of the sensing capacitor to the first power supply voltage, and a second charge transfer path is provided to transfer the charge stored in the storage capacitor to the variable And then compare the voltage of the storage capacitor after the charge is transferred to the variable capacitor with the second power supply voltage, and adjust the capacitance value of the variable capacitor according to the comparison result; and step D, repeat step B and step C, The capacitance detection circuit does not complete the adaptive capacitance mode until the voltage of the storage capacitor after the charge is transferred to the variable capacitor is equal to the second power supply voltage.

In addition, the embodiment of the present invention further provides an operating method for the capacitance detection circuit. The capacitance detection circuit has an adaptive capacitance mode and a touch button mode, and it includes a storage capacitor and a variable capacitor. The operation method includes the following steps. In the adaptive capacitance mode, the capacitance detection circuit is used to perform: Step A, providing a first charging path to charge the voltage of the sensing capacitor to the first power supply voltage, and providing a second charging path to charge the voltage of the storage capacitor to The second power supply voltage, wherein the second power supply voltage is less than the first power supply voltage, and the sensing capacitor includes parasitic capacitance and finger capacitance; step B, providing a discharge path to discharge the voltage of the variable capacitor to the ground voltage, and providing a first charge transfer path The charge stored in the sensing capacitor is transferred to the storage capacitor; step C, a first charging path is provided to charge the voltage of the sensing capacitor to the first power supply voltage, and a second charge transfer path is provided to transfer the charge stored in the storage capacitor to the variable And then compare the voltage of the storage capacitor after the charge is transferred to the variable capacitor with the second power supply voltage, and adjust the capacitance value of the variable capacitor according to the comparison result; and step D, repeat step B and step C, The capacitance detection circuit does not complete the adaptive capacitance mode until the voltage of the storage capacitor after the charge is transferred to the variable capacitor is equal to the second power supply voltage.

In order to further understand the features and technical content of the present invention, please refer to the following detailed description and drawings about the present invention. However, the provided drawings are only for reference and description, and are not used to limit the present invention.

The following are specific examples to illustrate the implementation of the present invention. Those skilled in the art can understand the advantages and effects of the present invention from the content provided in this specification. The present invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the concept of the present invention. In addition, the drawings of the present invention are merely schematic illustrations, and are not drawn according to actual dimensions, and are stated in advance. The following embodiments will further describe the related technical content of the present invention in detail, but the provided content is not intended to limit the protection scope of the present invention.

It should be understood that although terms such as “first”, “second”, and “third” may be used in this document to describe various elements or signals, these elements or signals should not be limited by these terms. These terms are mainly used to distinguish one element from another, or one signal from another signal. In addition, the term "or" used in this article should, depending on the actual situation, possibly include any one or a combination of more of the associated listed items.

Please refer to FIG. 2. FIG. 2 is a schematic diagram of a capacitance detection circuit provided by an embodiment of the present invention. The capacitance detection circuit 20 can also be integrated in a single chip, and it is also coupled to a microcontroller and at least one conductor used as a button (not shown in FIG. 2). For the convenience of the following description, the capacitance detection circuit 20 of FIG. 2 also only uses an example of coupling a conductor, but different from the capacitance detection circuit 10 of FIG. 1, the capacitance detection circuit 20 includes a storage capacitor Cs2 and a storage capacitor Cs2 connected in parallel. In addition to the variable capacitor Cr, it also includes a charge transfer structure composed of five switches SW1a, SW1b, SW2a, SW2b, and SW3a. In this embodiment, the capacitance detection circuit 20 is coupled to the conductor through the pin P1, and the switch SW1b is coupled between the node C and the storage capacitor Cs2, and the node C is located between the pin P1 and the switch SW1b.

In addition, the switch SW2a is coupled between the node C and the first power voltage Va, the switch SW3a is coupled between the second power voltage Vb and the storage capacitor Cs2, and the switch SW3a and the switch SW1b are commonly coupled to the storage capacitor Cs2 through the node D. The first terminal and the second terminal of the storage capacitor Cs2 are coupled to the ground voltage GND. Finally, the switch SW2b is coupled between the node D and the variable capacitor Cr, the switch SW1a is coupled between the ground voltage GND and the variable capacitor Cr, and the switch SW1a and the switch SW2b are jointly coupled to the first of the variable capacitor Cr through the node E At one end, the second end of the variable capacitor Cr is also coupled to the ground voltage GND. In other words, the capacitance detection circuit 20 may also include a path selection circuit (not shown in FIG. 2) for generating a plurality of control signals (not shown in FIG. 2) to respectively turn on or turn off the five switches SW1a, SW1b, SW2a, SW2b, SW3a ( Figure 2 is not shown), but the present invention does not limit the specific implementation of the path selection circuit, so the details will not be repeated here.

It should be noted that, compared to the operation method of the capacitance detection circuit 10, the capacitance detection circuit 20 is used to adjust the capacitance value of the variable capacitor Cr in an adaptive capacitance mode, and detect in a touch button mode. The capacitance value change of the sensing capacitor (Cd+Cf) is measured to generate the touch value related to the conductor (not shown in Figure 2). Therefore, as shown in FIG. 2, in the adaptive capacitance mode, the capacitance detection circuit 20 will first turn on the switch SW2a and the switch SW3a at the same time, so as to provide a first charging path to charge the voltage Vdf of the sensing capacitor (Cd+Cf) to The first power supply voltage Va and a second charging path are provided to charge the voltage Vcs2 of the storage capacitor Cs2 to the second power supply voltage Vb, and then the switch SW2a and the switch SW3a are turned off at the same time.

As mentioned above, in addition to the finger capacitance Cf, the inductive capacitance outside the chip also has a parasitic capacitance Cd mainly from the PCB. Therefore, in this embodiment, the inductive capacitance can be simplified as (Cd+Cf). In addition, the second power supply voltage Vb is less than the first power supply voltage Va, and the capacitance detection circuit 20 may further include an internal voltage regulator (not shown in FIG. 2) for generating the first power supply voltage Va and the second power supply voltage Vb. However, the present invention does not limit the specific implementation of the internal voltage regulator, so the details will not be repeated here. In summary, in this embodiment, it can be assumed that the first power supply voltage Va is 2 volts, and the second power supply voltage Vb is 1 volt (that is, Vb=Va/2).

Secondly, the capacitance detection circuit 20 turns on the switch SW1a and the switch SW1b at the same time, so as to provide a discharge path to discharge the voltage of the variable capacitor Cr to the ground voltage GND, and provide a first charge transfer path to store the sensing capacitor (Cd+Cf) The charge is transferred to the storage capacitor Cs2, and then the switch SW1a and the switch SW1b are turned off at the same time. Then, the capacitance detection circuit 20 turns on the switch SW2a and the switch SW2b at the same time, so that a first charging path is provided to charge the voltage Vdf of the sensing capacitor (Cd+Cf) to the first power supply voltage Va, and a second charge transfer path is provided to store The charge stored in the capacitor Cs2 is transferred to the variable capacitor Cr, and then the switch SW2a and the switch SW2b are turned off at the same time, and the voltage Vcs2 of the storage capacitor Cs2 after the charge is transferred to the variable capacitor Cr is compared with the second power supply voltage Vb, And according to the comparison result, the capacitance value of the variable capacitor Cr is adjusted.

For example, if the voltage Vcs2 at this time is greater than the second power supply voltage Vb, it means that the capacitance value of the variable capacitor Cr is too small, so the capacitance detection circuit 20 can be adjusted by a variable capacitance controller (not shown in FIG. 2) The capacitance value of the large variable capacitor Cr; relatively, if the voltage Vcs2 at this time is less than the second power supply voltage Vb, it means that the capacitance value of the variable capacitor Cr is too large, so the capacitance detection circuit 20 can be controlled by the variable capacitor controller The capacitance value of the variable capacitor Cr is reduced, but the present invention does not limit the specific implementation of the variable capacitor controller, so the details about it will not be repeated here. It should be noted that the capacitance detection circuit 20 can repeatedly provide the discharge path of the variable capacitor Cr plus the first charge transfer path and the first charge path plus the second charge transfer path, or cyclically turn on the switches SW1a plus SW1b and The switch SW2a adds SW2b until the voltage Vcs2 of the storage capacitor Cs2 after the charge is transferred to the variable capacitor Cr is equal to the second power supply voltage Vb, or the voltage Vcs2 and the second power supply voltage Vb approach the same, the capacitance detection circuit 20 does not count Complete the adaptive capacitance mode.

In other words, the purpose of the adaptive capacitance mode is to adjust the capacitance value of the variable capacitor Cr to be equal to or close to the capacitance value of the current sensing capacitor (Cd+Cf). In addition, it should be understood that the storage capacitor Cs2 is charged by the inductive capacitor (Cd+Cf), and the variable capacitor Cr is discharged by it. Therefore, in this embodiment, it is only necessary to design the storage capacitor Cs2 to be about 200 pF, so that it and the capacitance detection circuit 20 can be integrated into a single chip. In this way, the capacitance detection circuit 20 does not require an external capacitance component, so that it can avoid false detection caused by changes in environmental temperature and humidity. In contrast, the built-in small capacitance of about 200pF does not attenuate the change of the touch value, but can achieve a higher detection resolution.

In addition, in order to prevent the sensing capacitance (Cd+Cf) from changing due to external influences, the capacitance detection circuit 20 must first complete the adaptive capacitance mode before entering the touch button mode. In other words, the capacitance detection circuit 20 needs to perform the adaptive capacitance mode for a fixed period of time, and after entering the touch button mode, the capacitance detection circuit 10 is different from the capacitance detection circuit 10 in FIG. The comparator CP detects whether the voltage Vcs reaches the reference voltage Vref. The capacitance detection circuit 20 further includes a voltage-controlled oscillator (VCO) 201 for oscillating the first frequency and the second frequency at the same time (not shown in Figure 2), The first frequency is generated by the control of the voltage Vcs2, and the second frequency is generated by the control of the second power supply voltage Vb. Therefore, when the external power supply is interfered by noise, the voltage Vcs2 and the second power supply voltage Vb will also be interfered by the noise at the same time, and the frequencies of the first frequency and the second frequency are still close to the same, so that the capacitance detection circuit 20 The noise interference from the external power supply can be eliminated. In other words, the use of the voltage-controlled oscillator 201 can simultaneously reduce the noise interference of the external power supply, so as to achieve a higher detection resolution.

，其中

為在導通開關SW1b以將感應電容(Cd+Cf)所儲存的電荷轉移至儲存電容Cs2前的電壓Vcs2。另外，在導通開關SW2b以將儲存電容Cs2所儲存的電荷轉移至可變電容Cr後，儲存電容Cs2的電壓Vcs2又可表示為：

，其中

為在導通開關SW2b以將儲存電容Cs2所儲存的電荷轉移至可變電容Cr前的電壓Vcs2。由此可見，假如

，則每次從感應電容(Cd+Cf)轉移至儲存電容Cs2和從儲存電容Cs2轉移至可變電容Cr的電荷量相等，所以在完成自適應電容模式時，儲存電容Cs2的電壓Vcs2將等於第二電源電壓Vb，或者是說儲存電容Cs2的電壓Vcs2可穩定保持在第二電源電壓Vb附近，使得壓控振盪器201可穩定振盪出相同或趨近一致的第一頻率和第二頻率。由於調整可變電容Cr的細節已如同前述內容所述，故於此就不再多加贅述。 It should be noted that after the switch SW1b is turned on to transfer the charge stored in the sensing capacitor (Cd+Cf) to the storage capacitor Cs2, the voltage Vcs2 of the storage capacitor Cs2 can be expressed as:

,among them

It is the voltage Vcs2 before the switch SW1b is turned on to transfer the charge stored in the sensing capacitor (Cd+Cf) to the storage capacitor Cs2. In addition, after the switch SW2b is turned on to transfer the charge stored in the storage capacitor Cs2 to the variable capacitor Cr, the voltage Vcs2 of the storage capacitor Cs2 can be expressed as:

,among them

This is the voltage Vcs2 before the switch SW2b is turned on to transfer the charge stored in the storage capacitor Cs2 to the variable capacitor Cr. It can be seen that if

, The amount of charge transferred from the sensing capacitor (Cd+Cf) to the storage capacitor Cs2 and from the storage capacitor Cs2 to the variable capacitor Cr is equal each time, so when the adaptive capacitor mode is completed, the voltage Vcs2 of the storage capacitor Cs2 will be The second power supply voltage Vb, or the voltage Vcs2 of the storage capacitor Cs2, can be stably maintained near the second power supply voltage Vb, so that the voltage-controlled oscillator 201 can stably oscillate with the same or close to the same first frequency and second frequency. Since the details of adjusting the variable capacitor Cr are as described in the foregoing content, it will not be repeated here.

On the other hand, as shown in FIG. 2, in the touch button mode, the capacitance detection circuit 20 will first turn on the switch SW1a and the switch SW1b simultaneously, providing a discharge path to discharge the voltage of the variable capacitor Cr to the ground voltage GND, and A first charge transfer path is provided to transfer the charge stored in the sensing capacitor (Cd+Cf) to the storage capacitor Cs2, and then the switch SW1a and the switch SW1b are turned off at the same time. Secondly, the capacitance detection circuit 20 will simultaneously turn on the switch SW2a and the switch SW2b, so that a first charging path is provided to charge the voltage of the sensing capacitor (Cd+Cf) to the first power supply voltage Va, and a second charge transfer path is provided to store the capacitor The charge stored in Cs2 is transferred to the variable capacitor Cr, and then the switch SW2a and the switch SW2b are turned off at the same time, and the sensing capacitor is detected based on the voltage Vcs2 of the storage capacitor Cs2 after the charge is transferred to the variable capacitor Cr (Cd+Cf) The capacitance value changes.

Please note that it can be clearly understood from the foregoing that the capacitance detection circuit 20 does not use the voltage detection value, but in fact, the first frequency and the second frequency oscillated by the voltage controlled oscillator 201 still reflect the voltage Vcs2 and the second power supply. Voltage Vb. Therefore, the capacitance detection circuit 20 at this time can still be regarded as comparing the voltage Vcs2 of the storage capacitor Cs2 after the charge is transferred to the variable capacitor Cr with the second power supply voltage Vb, and detecting the sensing capacitor (Cd +Cf) changes in capacitance. For example, if the voltage Vcs2 at this time is equal to the second power supply voltage Vb, it means that the capacitance value of the sensing capacitor (Cd+Cf) has not changed. In contrast, if the voltage Vcs2 at this time is greater than the second power supply voltage Vb, it means that the capacitance value of the inductive capacitor (Cd+Cf) becomes larger, so the capacitance detection circuit 20 can repeatedly provide the discharge path of the variable capacitor Cr plus the second A charge transfer path and the first charge path plus the second charge transfer path, or cyclically turn on the switch SW1a plus SW1b and the switch SW2a plus SW2b, until a fixed time later, if the voltage Vcs2 and the second power supply voltage Vb are different When the voltage gap becomes larger and larger, or the voltage gap tends to stabilize, the microcontroller at this time can judge that the finger (not shown in Figure 2) has pressed the conductor according to the change in the capacitance value of the sensing capacitor (Cd+Cf), and if If the voltage gap between the voltage Vcs2 and the second power supply voltage Vb becomes smaller and smaller, the microcontroller can also determine that the finger is moving away from the conductor.

In addition, as shown in FIG. 2, the capacitance detection circuit 20 may further include a counter 203, coupled to the voltage-controlled oscillator 201, for storing at least one value generated by the voltage-controlled oscillator 201, and according to the at least one value, the counter 203 can generate a touch value to reflect the change of the capacitance value of the sensing capacitor (Cd1+Cf1). For example, when a finger presses the conductor, even if the parasitic capacitance Cd remains unchanged, the finger capacitance Cf changes from 0pF to about 0.5pF, so that the charging increases, causing the voltage Vcs2 to rise, and the voltage controlled oscillator 201 The first frequency of oscillation also rises relatively. Therefore, within a fixed period of time, the value stored in the counter 203 will increase and a corresponding touch value will be generated, so that the microcontroller can determine that the finger presses the conductor according to the touch value. In contrast, when the finger leaves the conductor, the finger capacitance Cf returns to 0 pF, so that the charging is reduced, so that the voltage Vcs2 drops, and the first frequency oscillated by the voltage controlled oscillator 201 also drops relatively. Therefore, within a fixed period of time, the value stored in the counter 203 will become smaller and a corresponding touch value will be generated, so that the microcontroller can determine according to the touch value that the finger is not pressing the conductor. In a word, the operating principle of the touch value generated by the counter 203 and the touch value of the microcontroller to determine the state of the finger pressing the key by the touch value on the counter 203 are all known to those with ordinary knowledge in the art, so the details are I won't repeat it again.

It is worth mentioning that, as mentioned above, the capacitance value of the parasitic capacitance Cd is not consistent on each touch button (ie, conductor). Therefore, for products with multiple touch buttons, the capacitance detection circuit 20 can make each touch button have a capacitance value corresponding to a variable capacitance Cr, and by adjusting the capacitance value in the adaptive capacitance mode The capacitance value of the variable capacitor Cr makes the touch value of each touch button on the counter 203 consistent. In other words, this embodiment can solve the problem of inconsistent touch values caused by different parasitic capacitances Cd when multiple touch buttons are arranged on the PCB.

Finally, in order to further explain the operation flow of the capacitance detection circuit 20, the present invention further provides an embodiment of its operation method. Please refer to FIG. 3, which is a flow chart of the steps of the operation method provided by the embodiment of the present invention. It should be noted that the operation method of FIG. 3 can be used in the capacitance detection circuit 20 of FIG. 2. Therefore, please refer to FIG. 2 for better understanding, but the present invention does not limit the operation method of FIG. In the capacitance detection circuit 20 of FIG. 2. Similarly, for the convenience of the following description, FIG. 3 only shows that the capacitance detection circuit 20 is an operation method of coupling one conductor, but for the capacitance detection circuit 20 is an operation method of coupling multiple conductors, there is general knowledge in the art It should be modified and expanded by the content provided in this manual. In addition, since the detailed step flow is as described in the foregoing embodiment, it is only summarized here and will not be redundantly described.

As shown in FIG. 3, in step S301 in the adaptive capacitance mode, a first charging path is provided to charge the voltage Vdf of the sensing capacitor (Cd+Cf) to the first power supply voltage Va, and a second charging path is provided to charge the storage capacitor The voltage Vcs2 of Cs2 is charged to the second power supply voltage Vb. Next, in step S302 in the adaptive capacitance mode, a discharge path is provided to discharge the voltage of the variable capacitor Cr to the ground voltage GND, and a first charge transfer path is provided to transfer the charge stored in the sensing capacitor (Cd+Cf) to Storage capacitor Cs2.

Next, in step S303 in the adaptive capacitance mode, a first charging path is provided to charge the voltage Vdf of the sensing capacitor (Cd+Cf) to the first power supply voltage Va, and a second charge transfer path is provided to store the storage capacitor Cs2 The charge is transferred to the variable capacitor Cr. Then, in step S304 in the adaptive capacitance mode, it is checked whether the voltage Vcs2 of the storage capacitor Cs2 after the charge is transferred to the variable capacitor Cr is equal to the second power supply voltage Vb. If not, step S305 is executed to adjust the capacitance value of the variable capacitor Cr according to the comparison result of the voltage Vcs2 and the second power supply voltage Vb, and after step S305 is completed, step S302 to step S304 are returned to. In other words, steps S302 to S305 are repeatedly executed until the voltage Vcs2 of the storage capacitor Cs2 after the charge is transferred to the variable capacitor Cr is equal to the second power supply voltage Vb, and then the capacitance detection circuit 20 is considered to be the completion of the adaptive capacitor mode.

In addition, in step S306 in the touch key mode, a discharge path is provided to discharge the voltage of the variable capacitor Cr to the ground voltage GND, and a first charge transfer path is provided to transfer the charge stored in the sensing capacitor (Cd+Cf) to Storage capacitor Cs2. Next, in step S307 in the touch key mode, a first charging path is provided to charge the voltage of the sensing capacitor (Cd+Cf) to the first power supply voltage Va, and a second charge transfer path is provided to store the storage capacitor Cs2 The charge is transferred to the variable capacitor Cr. Then, in step S308 in the touch key mode, the capacitance value change of the sensing capacitor (Cd+Cf) is detected according to the voltage Vcs2 of the storage capacitor Cs2 after the charge is transferred to the variable capacitor Cr, and the step S308 is completed After that, return to step S306 to step S308. In other words, steps S306 to S308 are repeatedly executed, so that the capacitance detection circuit 20 can generate a touch value related to the conductor to reflect the capacitance value change of the sensing capacitor (Cd+Cf).

In summary, the embodiments of the present invention provide a capacitance detection circuit and an operating method thereof. The storage capacitor is integrated into a single chip to avoid false detection caused by changes in environmental temperature and humidity. In adaptive capacitance mode, adjust the capacitance value of the variable capacitor, so that the touch value of each touch button on the counter can be consistent, or it can solve the problem of different parasitic capacitances when multiple touch buttons are arranged on the PCB. The resulting inconsistent touch values. In addition, the capacitance detection circuit uses a voltage-controlled oscillator, which can simultaneously reduce the noise interference of the external power supply to achieve a higher detection resolution.

The content provided above is only the preferred and feasible embodiments of the present invention, and does not limit the scope of the patent application of the present invention. Therefore, all equivalent technical changes made using the description and schematic content of the present invention are included in the application of the present invention. Within the scope of the patent.

10.20: Capacitance detection circuit 11: fingers 12: Conductor 101: Voltage Detector 201: Voltage Controlled Oscillator 203: Counter CP: Comparator Cs, Cs2: storage capacitor Cf: Finger capacitance Cd: Parasitic capacitance Cr: variable capacitance SW1, SW2, SW3, SW1a, SW1b, SW2a, SW2b, SW3a: switch VDD, Va, Vb: power supply voltage GND: Ground voltage Vref: reference voltage Vcs, Vcs2, Vdf: voltage A, B, C, D, E: node P1: pin S301～S308: Process steps

Figure 1 is a schematic diagram of a conventional capacitance detection circuit.

FIG. 2 is a schematic diagram of a capacitance detection circuit provided by an embodiment of the present invention.

FIG. 3 is a flow chart of the steps of the operation method provided by the embodiment of the present invention.

20: Capacitance detection circuit

201: Voltage Controlled Oscillator

203: Counter

Cs2: storage capacitor

Cf: Finger capacitance

Cd: Parasitic capacitance

Cr: variable capacitance

SW1a, SW1b, SW2a, SW2b, SW3a: switch

Va, Vb: power supply voltage

GND: Ground voltage

Vcs2, Vdf: voltage

C, D, E: node

P1: pin

Claims (9)

A capacitance detection circuit is coupled to a conductor. The capacitance detection circuit includes: a storage capacitor and a variable capacitor. The capacitance detection circuit is used to adjust the capacitance value of the variable capacitor in an adaptive capacitance mode; In a touch button mode, the capacitance value of a sensing capacitor is detected to generate a touch value related to the conductor. In the adaptive capacitance mode, the capacitance detection circuit is used to perform: step S1, A first charging path is provided to charge the voltage of the sensing capacitor to a first power supply voltage, and a second charging path is provided to charge the voltage of the storage capacitor to a second power supply voltage, wherein the second power supply voltage is less than the first power supply voltage. A power supply voltage, and the inductive capacitor includes a parasitic capacitor and a finger capacitor; step S2, provide a discharge path to discharge the voltage of the variable capacitor to a ground voltage, and provide a first charge transfer path to the inductive capacitor The stored charge is transferred to the storage capacitor; step S3, the first charging path is provided to charge the voltage of the sensing capacitor to the first power supply voltage, and a second charge transfer path is provided to transfer the charge stored in the storage capacitor To the variable capacitor, and then compare the voltage of the storage capacitor after the charge is transferred to the variable capacitor with the second power supply voltage, and adjust the capacitance value of the variable capacitor according to the comparison result; and Step S4, repeat the steps S2 and S3, until the voltage of the storage capacitor after the charge is transferred to the variable capacitor is equal to the second power supply voltage, the capacitance detection circuit completes the adaptive capacitor mode; In the touch key mode, the capacitance detection circuit is used to perform: step S5, providing the discharge path to discharge the voltage of the variable capacitor to the ground voltage, and providing the first charge transfer path to The charge stored in the sensing capacitor is transferred to the storage capacitor; step S6, providing the first charging path to charge the voltage of the sensing capacitor to the first power supply voltage, and providing the second charge transfer path to the storage capacitor The stored charge is transferred to the variable capacitor, and then the capacitance value change of the sensing capacitor is detected according to the voltage of the storage capacitor after the charge is transferred to the variable capacitor; and step S7, repeating step S5 And this step S6 enables the capacitance detection circuit to generate the touch value to reflect the change of the capacitance value of the sensing capacitor. The capacitance detection circuit according to claim 1, wherein the capacitance detection circuit is coupled to the conductor through a first node, and the capacitance detection circuit further includes: a first switch coupled to the first node And the storage capacitor; a second switch, coupled between the first node and the first power voltage; A third switch is coupled between the second power supply voltage and the storage capacitor, and the third switch and the first switch are commonly coupled to the first end of the storage capacitor through a second node. The first end of the storage capacitor is The two ends are coupled to the ground voltage; a fourth switch is coupled between the second node and the variable capacitor; and a fifth switch is coupled between the ground voltage and the variable capacitor, and the first The fifth switch and the fourth switch are jointly coupled to the first terminal of the variable capacitor through a third node, and the second terminal of the variable capacitor is coupled to the ground voltage. The capacitance detection circuit according to claim 2, wherein the storage capacitor and the capacitance detection circuit are integrated in a single chip, and the capacitance detection circuit further includes: a path selection circuit for generating a plurality of control signals, The first to fifth switches are turned on or off respectively; an internal voltage regulator is used to generate the first power voltage and the second power voltage; and a variable capacitance controller is used according to the step S3 The comparison result is used to adjust the capacitance value of the variable capacitor. The capacitance detection circuit described in claim 2 further includes: A voltage controlled oscillator is used to oscillate a first frequency and a second frequency simultaneously, wherein the first frequency is generated by the voltage control of the storage capacitor, and the second frequency is generated by the second power supply voltage And a counter, coupled to the voltage-controlled oscillator, for storing at least one value generated by the voltage-controlled oscillator, and according to the at least one value, the counter can generate the touch value to reflect the The capacitance value of the sensing capacitor changes. The capacitance detection circuit according to claim 1, wherein in the comparison result of the step S3, if the voltage of the storage capacitor is greater than the second power supply voltage, the capacitance detection circuit increases the variable capacitor If the voltage of the storage capacitor is less than the second power supply voltage, the capacitance detection circuit reduces the capacitance value of the variable capacitor. The capacitance detection circuit according to claim 5, wherein in detecting the change in the capacitance value of the sensing capacitor based on the voltage of the storage capacitor after the charge is transferred to the variable capacitor, if the storage capacitor is If the voltage is greater than the second power supply voltage, it means that the capacitance value of the sensing capacitor becomes larger, and after repeating the step S5 and the step S6 for a fixed period of time, if the voltage of the storage capacitor and the second power supply voltage The voltage gap tends to stabilize, and the capacitance detection circuit determines that a finger presses the conductor according to the touch value. An operating method for a capacitance detection circuit. The capacitance detection circuit has an adaptive capacitance mode and a touch button mode, and is coupled to a conductor. The capacitance detection circuit includes a storage capacitor and a variable capacitor , The method of operation includes: In the adaptive capacitance mode, the capacitance detection circuit is used to perform: step S1, providing a first charging path to charge the voltage of an inductive capacitor to a first power supply voltage, and providing a second charging path to store the The voltage of the capacitor is charged to a second power supply voltage, where the second power supply voltage is less than the first power supply voltage, and the inductive capacitor includes a parasitic capacitor and a finger capacitor; step S2, a discharge path is provided for the variable capacitor The voltage is discharged to a ground voltage, and a first charge transfer path is provided to transfer the charge stored in the sensing capacitor to the storage capacitor; step S3, the first charging path is provided to charge the voltage of the sensing capacitor to the first Supply voltage, and provide a second charge transfer path to transfer the charge stored in the storage capacitor to the variable capacitor, and then compare the voltage of the storage capacitor after the charge is transferred to the variable capacitor and the second power supply The voltage is compared, and the capacitance value of the variable capacitor is adjusted according to the comparison result; and step S4, step S2 and step S3 are repeated until the voltage of the storage capacitor after the charge is transferred to the variable capacitor When equal to the second power supply voltage, the capacitance detection circuit completes the adaptive capacitance mode. The operating method further includes: in the touch key mode, the capacitance detection circuit is used to: Step S5, providing the discharge path to discharge the voltage of the variable capacitor to the ground voltage, and providing the first charge transfer path to transfer the charge stored in the sensing capacitor to the storage capacitor; step S6, providing the first A charging path charges the voltage of the sensing capacitor to the first power supply voltage, and provides the second charge transfer path to transfer the charge stored in the storage capacitor to the variable capacitor, and then transfer to the variable capacitor according to the charge The voltage of the storage capacitor after the variable capacitor is used to detect the change in the capacitance value of the sensing capacitor; and step S7, repeating the step S5 and the step S6, so that the capacitance detection circuit can generate a touch on the conductor Value to reflect the change of the capacitance value of the sensing capacitor. The operation method according to claim 7, wherein in the comparison result of step S3, if the voltage of the storage capacitor is greater than the second power supply voltage, the capacitance detection circuit increases the value of the variable capacitor The capacitance value, and if the voltage of the storage capacitor is less than the second power supply voltage, the capacitance detection circuit reduces the capacitance value of the variable capacitor. The operation method according to claim 8, wherein in detecting the change in the capacitance value of the sensing capacitor according to the voltage of the storage capacitor after the charge is transferred to the variable capacitor, if the voltage of the storage capacitor is If it is greater than the second power supply voltage, it means that the capacitance value of the sensing capacitor becomes larger, and the steps S5 and S5 are repeated. After a fixed time of step S6, if the voltage difference between the voltage of the storage capacitor and the second power supply voltage stabilizes, the capacitance detection circuit determines that a finger presses the conductor according to the touch value.

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