Capacitance detection circuit, touch chip and electronic device

Abstract

The application discloses a kind of capacitance detection circuit, touch chip and electronic equipment, the capacitance detection circuit includes: detection capacitance;Marking drive circuit, marking drive circuit is used to periodically alternate output first marking drive signal and second marking drive signal;Capacitance-voltage conversion circuit, for when marking drive circuit outputs first marking drive signal, according to the capacitance value of detection capacitance and first marking drive signal output corresponding first total voltage signal, and when marking drive circuit outputs second marking drive signal, according to the capacitance value of detection capacitance and second marking drive signal, output corresponding second total voltage signal;Signal processing circuit, for signal processing to first total voltage signal and second total voltage signal, to obtain the capacitance change of detection capacitance.The application can solve the problem of low sensitivity of existing capacitance detection circuit.

Description

Technical Field

[0001] This invention relates to the field of capacitance detection technology, and in particular to a capacitance detection circuit, a touch chip, and an electronic device. Background Technology

[0002] Currently, touchscreens are used in electronic devices such as mobile phones, PDAs (Personal Digital Assistants), GPS (Global Positioning System), PMPs (MP3, MP4, etc.), and even tablets. Touchscreens offer advantages such as simple, convenient, and user-friendly operation, making them a promising interface for human-computer interaction and leading to their widespread adoption in portable devices. With the widespread use of touchscreens, research into touchscreen technology is becoming increasingly in-depth. Existing technologies often determine whether a touchscreen unit has been touched by detecting its self-capacitance. Therefore, accurately detecting the self-capacitance generated when a touchscreen unit is touched is crucial. However, traditional switch-controlled discrete capacitance detection circuits can only acquire a single signal, resulting in low sensitivity and failing to meet the requirements of applications with high sensitivity requirements. Summary of the Invention

[0003] The main objective of this invention is to propose a capacitance detection circuit that addresses the problem of low sensitivity in existing capacitance detection circuits.

[0004] To achieve the above objectives, the present invention provides a capacitance detection circuit comprising:

[0005] A detection capacitor is used to detect external sensing signals and output the corresponding capacitance value.

[0006] A coding driving circuit is used to periodically and alternately output a first coding driving signal and a second coding driving signal.

[0007] A capacitor-to-voltage circuit is provided, wherein a first input terminal of the capacitor-to-voltage circuit is connected to the detection capacitor, and a second input terminal of the capacitor-to-voltage circuit is connected to the output terminal of the coding drive circuit. The capacitor-to-voltage circuit is used to output a corresponding first total voltage signal according to the capacitance value of the detection capacitor and the first coding drive signal when the coding drive circuit outputs a first coding drive signal, and to output a corresponding second total voltage signal according to the capacitance value of the detection capacitor and the second coding drive signal when the coding drive circuit outputs a second coding drive signal.

[0008] The signal processing circuit has its receiving end connected to the output end of the capacitor-to-voltage circuit. The signal processing circuit is also used to process the first total voltage signal and the second total voltage signal to obtain the capacitance change of the detection capacitor.

[0009] Optionally, the capacitance detection circuit further includes:

[0010] A voltage cancellation circuit, connected to the first input terminal of the capacitor-to-voltage conversion circuit, is configured to output a first cancellation signal to the capacitor-to-voltage conversion circuit when the coding drive circuit outputs a first coding drive signal, so that the capacitor-to-voltage conversion circuit cancels the base voltage signal according to the first cancellation signal, converts the first total voltage signal into a corresponding first voltage change signal, and then outputs it; and...

[0011] The voltage cancellation circuit is also used to output a second cancellation signal to the capacitor-to-voltage circuit when the coding drive circuit outputs a second coding drive signal, so that the capacitor-to-voltage circuit cancels the basic voltage signal according to the second cancellation signal, converts the second total voltage signal into a corresponding second voltage change signal, and then outputs it.

[0012] The signal processing circuit is also used to process the first voltage change signal and the second voltage change signal to obtain the change in the detection capacitor.

[0013] Optionally, the voltage cancellation circuit includes:

[0014] A cancelling capacitor, the first terminal of which is connected to the first input terminal of the capacitor-to-voltage circuit;

[0015] A cancellation voltage output circuit, the output terminal of which is connected to the second terminal of the cancellation capacitor, is used to output a first cancellation voltage to the cancellation capacitor when the coding drive circuit outputs a first coding drive signal, so that the cancellation capacitor outputs a first cancellation signal to the capacitor-to-voltage conversion circuit; and...

[0016] The offset voltage output circuit is also used to output a second offset voltage to the offset capacitor when the coding drive circuit outputs a second coding drive signal, so that the offset capacitor outputs a second offset signal to the capacitor-to-voltage circuit.

[0017] Optionally, the voltage cancellation output circuit includes a first switch, a second switch, a first voltage cancellation source, and a second voltage cancellation source;

[0018] The first switch is connected in series between the canceling capacitor and the first canceling voltage source. When the first switch is turned on, it controls the first canceling voltage source to be electrically connected to the canceling capacitor, so that the canceling capacitor outputs a first canceling signal to the capacitor-to-voltage circuit.

[0019] The second switch is connected in series between the canceling capacitor and the second canceling voltage source. When the second switch is turned on, it controls the second canceling voltage source to be electrically connected to the canceling capacitor, so that the canceling capacitor outputs a second canceling signal to the capacitor-to-voltage circuit.

[0020] Optionally, the capacitance detection circuit further includes:

[0021] A reference circuit is provided, the output of which is connected to the output of the capacitor-to-voltage circuit. The reference circuit is used to output a reference voltage as a reference value for the first total voltage signal and the second total voltage signal.

[0022] Optionally, the capacitance detection circuit as described in claim 1 is characterized in that the coding driving circuit includes a third switch, a fourth switch, a first coding voltage source, and a second coding voltage source.

[0023] The third switch is connected in series between the first coding voltage source and the capacitor-to-voltage circuit. The third switch is used to control the first coding voltage source and the capacitor-to-voltage circuit to be electrically connected when the circuit is turned on, so as to output the first coding drive signal to the capacitor-to-voltage circuit.

[0024] The fourth switch is connected in series between the second coding voltage source and the capacitor-to-voltage circuit. When the fourth switch is turned on, it controls the second coding voltage source to be electrically connected to the capacitor-to-voltage circuit so as to output the second coding drive signal to the capacitor-to-voltage circuit.

[0025] Optionally, the capacitor-to-voltage circuit includes an operational amplifier, a feedback capacitor, a fifth switch, and a sixth switch. The inverting input of the operational amplifier is connected to the detection capacitor, the non-inverting input of the operational amplifier is connected to the output of the coding drive circuit, the output of the operational amplifier is connected to the first terminal of the fifth switch, the second terminal of the fifth switch is connected to the receiving terminal of the signal processing circuit, the first terminal of the sixth switch is connected to the inverting input of the operational amplifier, the second terminal of the sixth switch is connected to the output of the operational amplifier, the first terminal of the feedback capacitor is connected to the inverting input of the operational amplifier, and the second terminal of the feedback capacitor is connected to the second terminal of the fifth switch.

[0026] Optionally, the signal processing circuit includes:

[0027] An analog-to-digital converter (ADC) is provided, the input of which is connected to the output of the programmable gain amplifier. The ADC is used to convert the total voltage signal output by the capacitor-to-voltage circuit into an analog-to-digital signal and then output it.

[0028] A signal processor, the input of which is connected to the output of the analog-to-digital converter, is used to process the first total voltage signal and the second total voltage signal output by the analog-to-digital converter to obtain the capacitance change of the detection capacitor.

[0029] The present invention also proposes a touch chip, which includes the above-described capacitance detection circuit.

[0030] The present invention also proposes an electronic device, which includes the touch chip described above; or, includes the capacitance detection circuit described above.

[0031] In this invention, a coding drive circuit generates and outputs two driving signals: a first coding drive signal and a second coding drive signal. When the capacitor-to-voltage circuit receives the first coding drive signal, it outputs a first total voltage signal, which includes the signal quantity indicating a change in the capacitance value of the detected capacitor. Similarly, when the capacitor-to-voltage circuit receives the second coding drive signal, it outputs a second total voltage signal, which also includes the signal quantity indicating a change in the capacitance value of the detected capacitor. Thus, by setting the coding drive circuit to output two driving signals, double the signal quantity is obtained. This allows the signal processing circuit to obtain the capacitance change value of the detected capacitor more accurately based on the first and second total voltage signals, thereby improving the sensitivity of capacitance detection. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0033] Figure 1 This is a functional module diagram of an embodiment of the capacitance detection circuit of the present invention;

[0034] Figure 2 This is a functional module diagram of an embodiment of the capacitance detection circuit of the present invention;

[0035] Figure 3 This is a circuit structure diagram of a prior art capacitance detection circuit;

[0036] Figure 4 This is a switching timing diagram of an embodiment of the capacitance detection circuit of the present invention;

[0037] Figure 5 This is a circuit structure diagram of an embodiment of the capacitance detection circuit of the present invention.

[0038] Explanation of icon numbers:

[0039] label name label name 10 Detection capacitor 60 Reference circuit 20 Coding driver circuit <![CDATA[C tp ]]> Detection capacitor 30 Capacitor-to-voltage circuit <![CDATA[C c ]]> Cancelling capacitor 40 Signal processing circuit <![CDATA[C f ]]> Feedback capacitor 50 Voltage cancellation circuit ADC Analog-to-digital converter

[0040] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0043] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0044] This invention proposes a capacitance detection circuit.

[0045] Currently, traditional switch-controlled discrete capacitance detection circuits can only acquire a single signal quantity during detection, resulting in low sensitivity and failing to meet the requirements of some applications with high sensitivity requirements for capacitance detection circuits.

[0046] To solve the above problems, refer to Figures 1 to 3 In one embodiment, the capacitance detection circuit includes:

[0047] The detection capacitor 10 is used to detect external sensing signals and output the corresponding capacitance value.

[0048] The coding driving circuit 20 is used to periodically and alternately output a first coding driving signal and a second coding driving signal.

[0049] A capacitor-to-voltage circuit 30 is provided. The first input terminal of the capacitor-to-voltage circuit 30 is connected to the detection capacitor 10, and the second input terminal of the capacitor-to-voltage circuit 30 is connected to the output terminal of the coding drive circuit 20. The capacitor-to-voltage circuit 30 is used to output a corresponding first total voltage signal according to the capacitance value of the detection capacitor 10 and the first coding drive signal when the coding drive circuit 20 outputs a first coding drive signal, and to output a corresponding second total voltage signal according to the capacitance value of the detection capacitor 10 and the second coding drive signal when the coding drive circuit 20 outputs a second coding drive signal.

[0050] The signal processing circuit 40 has its receiving end connected to the output end of the capacitor-to-voltage circuit 30. The signal processing circuit 40 is also used to process the first total voltage signal and the second total voltage signal to obtain the capacitance change of the detection capacitor 10.

[0051] In this embodiment, the detection capacitor 10 can be implemented using a variable capacitor, such as a variable-gap capacitor, a variable-area capacitor, or a variable-dielectric capacitor. According to the capacitance formula C = εA / δ, where ε is the dielectric constant of the two electrodes, A is the area covered by the electrodes, and δ is the distance between the electrodes, when the dielectric constant and area are constant, the smaller the distance between the electrodes, the larger the capacitance; conversely, the larger the distance, the smaller the capacitance. Thus, when the detection capacitor 10 receives external sensing signals, such as sound, pressure, or vibration, the pressure-sensitive film will displace, causing a change in the distance between the pressure-sensitive film and the substrate electrodes, thereby altering the capacitance between them and achieving the detection of the sensing signal.

[0052] The coding drive circuit 20 can be implemented using two voltage sources and switching transistors. By controlling the switch to switch between different voltage sources, the coding drive circuit 20 can output a first coding drive signal and a second coding drive signal. The two switching transistors can be interlocked, that is, when one switching transistor is turned on, the other switching transistor is turned off. The two switching transistors periodically alternate on and off, so that the coding drive circuit 20 can periodically alternately output the first coding drive signal and the second coding drive signal.

[0053] The capacitor-to-voltage circuit 30 can be implemented using a comparator and a feedback capacitor. The positive input of the comparator is connected to the coding drive circuit 20 to receive the first coding drive signal and the second coding drive signal, while the inverting input is connected to the detection capacitor 10. Thus, the comparator can output the corresponding first total voltage signal and second total voltage signal based on the first coding drive signal, the second coding drive signal, and the capacitance value of the detection capacitor 10, effectively converting the capacitance of the detection capacitor 10 into a voltage value. When the signal processing circuit 40 receives the first total voltage signal and the second total voltage signal output from the capacitor-to-voltage circuit 30, it can obtain the capacitance change value of the detection capacitor 10 through table lookup, quadrature demodulation, and Fourier transform, thereby obtaining the sensing signal or other parameters detected by the detection capacitor 10 based on the capacitance change value.

[0054] Understandably, in traditional switch-controlled discrete capacitance detection circuits, a fixed reference voltage is connected to the positive input terminal of the amplifier during detection. Therefore, traditional capacitance detection circuits can only acquire a single signal, resulting in low sensitivity.

[0055] Therefore, in the technical solution of this invention, a coding drive circuit 20 is used to generate and output two drive signals: a first coding drive signal and a second coding drive signal. When the capacitor-to-voltage circuit 30 receives the first coding drive signal, it outputs a first total voltage signal, which includes the signal quantity indicating a change in the capacitance value of the detection capacitor 10. When the capacitor-to-voltage circuit 30 receives the second coding drive signal, it outputs a second total voltage signal, which also includes the signal quantity indicating a change in the capacitance value of the detection capacitor 10. Thus, by setting the coding drive circuit 20 to output two drive signals, double the signal quantity is obtained, making it more accurate for the signal processing circuit 40 to obtain the capacitance change value of the detection capacitor 10 based on the first and second total voltage signals, thereby improving the sensitivity of capacitance detection.

[0056] Reference Figures 1 to 3 In one embodiment, the capacitance detection circuit further includes:

[0057] A voltage cancellation circuit 50 is connected to the first input terminal of the capacitor-to-voltage circuit 30. The voltage cancellation circuit 50 is used to output a first cancellation signal to the capacitor-to-voltage circuit 30 when the coding drive circuit 20 outputs a first coding drive signal. This allows the capacitor-to-voltage circuit 30 to cancel the base voltage signal according to the first cancellation signal, convert the first total voltage signal into a corresponding first voltage change signal, and then output it.

[0058] The voltage cancellation circuit 50 is also used to output a second cancellation signal to the capacitor-to-voltage circuit 30 when the coding drive circuit 20 outputs a second coding drive signal, so that the capacitor-to-voltage circuit 30 cancels the basic voltage signal according to the second cancellation signal, converts the second total voltage signal into a corresponding second voltage change signal and outputs it.

[0059] The signal processing circuit 40 is also used to process the first voltage change signal and the second voltage change signal to obtain the change in the detection capacitor 10.

[0060] It is understandable that when the detection capacitor 10 does not detect an external sensing signal, that is, when the capacitance value of the detection capacitor 10 does not change, the capacitor-to-voltage circuit 30 will output a basic voltage signal. At this time, this basic voltage signal represents the basic capacitance value of the detection capacitor 10. Therefore, in this embodiment, the voltage cancellation circuit 50 can be implemented using a cancellation capacitor, a voltage source, and a switching transistor to generate and output the first cancellation signal and the second cancellation signal. By setting up a voltage cancellation circuit 50 to generate and output a first cancellation signal and a second cancellation signal, the basic voltage signal portions representing the basic capacitance value of the detection capacitor 10 in the first total voltage signal and the second total voltage signal are respectively cancelled out, so that the capacitor-to-voltage circuit 30 outputs a first voltage change signal and a second voltage change signal representing the capacitance change of the detection capacitor 10. The first coding drive signal and the second coding drive signal can be level signals with different voltage values. Thus, the first voltage change signal and the second voltage change signal are a pair of signal groups with the same amplitude but opposite phase. They are voltage signals symmetrical about the average voltage values ​​of the first coding drive signal and the second coding drive signal. The same capacitance change is represented by two signals with different polarities. Therefore, a capacitance change can be represented by twice the signal amount.

[0061] Optionally, the voltage cancellation circuit 50 includes:

[0062] A cancelling capacitor, the first end of which is connected to the first input terminal of the capacitor-to-voltage circuit 30;

[0063] A cancellation voltage output circuit, the output terminal of which is connected to the second terminal of the cancellation capacitor, is used to output a first cancellation voltage to the cancellation capacitor when the coding drive circuit 20 outputs a first coding drive signal, so that the cancellation capacitor outputs a first cancellation signal to the capacitor-to-voltage conversion circuit 30; and...

[0064] The offset voltage output circuit is also used to output a second offset voltage to the offset capacitor when the coding drive circuit 20 outputs a second coding drive signal, so that the offset capacitor outputs a second offset signal to the capacitor-to-voltage circuit 30.

[0065] In this embodiment, the cancellation voltage output circuit can be implemented using two voltage sources and switching transistors. By controlling the switch to switch between different voltage sources, the cancellation voltage output circuit can output a first cancellation voltage and a second cancellation voltage to the cancellation capacitor. The two switching transistors can be interlocked, that is, when one switching transistor is turned on, the other switching transistor is turned off. The two switching transistors periodically alternate on and off, so that the coding drive circuit 20 can periodically alternately output the first cancellation voltage and the second cancellation voltage. It is understandable that, in order to cancel out the base voltage signal portion representing the base capacitance value of the detection capacitor 10 in the first total voltage signal when the coding drive circuit 20 outputs the first coding drive signal, the cancellation voltage output circuit should synchronously output the first cancellation voltage when the coding drive circuit 20 outputs the first coding drive signal. Therefore, the switching transistor in the cancellation voltage output circuit can be linked with the switching transistor in the coding drive circuit 20, so that the cancellation voltage output circuit synchronously outputs the first cancellation voltage when the coding drive circuit 20 outputs the first coding drive signal, and synchronously outputs the second cancellation voltage when the coding drive circuit 20 outputs the second coding drive signal, so as to cancel out the base voltage signal portion representing the base capacitance value of the detection capacitor 10 in the first total voltage signal and the second total voltage signal, so that the capacitor-to-voltage circuit 30 outputs the first voltage change signal and the second voltage change signal representing the capacitance change of the detection capacitor 10.

[0066] In addition, refer to Figure 5 In one embodiment, the cancelling capacitor C C It can be derived from the formula.

[0067]

[0068] As can be seen from the above formula, although C is added to the molecule f The amount of C, but C f Usually less than C tp From the denominator (V) of the above equation CP -V CN )-(V H -V L It can be seen that if V is increased... CP -V CN The value of V, or decrease V H -V L If the value of is increased, the value of the denominator can be increased, thereby increasing the compensation capacitor C. CThe value decreases, meaning that for the same C in existing capacitance detection circuits... tp The required cancellation capacitor C in this application C The value will decrease. Therefore, in the technical solution of the present invention, the capacitance value of the cancellation capacitor can be reduced by adjusting the coding voltage and the cancellation voltage, thereby reducing the volume of the cancellation capacitor, which in turn effectively reduces the area of ​​the chip, reduces the overall volume of the capacitance detection circuit, and improves the practicality and stability of the capacitance detection circuit.

[0069] Reference Figures 1 to 3 In one embodiment, the capacitance detection circuit further includes:

[0070] A reference circuit 60 is provided, the output of which is connected to the output of the capacitor-to-voltage circuit 30. The reference circuit 60 is used to output a reference voltage as a reference value for the first total voltage signal and the second total voltage signal.

[0071] In this embodiment, the reference circuit 60 can be implemented using a reference voltage source and a switching transistor. The reference voltage source is connected to the output terminal of the capacitor-to-voltage circuit 30, and the reference voltage output by the reference circuit 60 is used as the reference value of the first total voltage signal and the second total voltage signal. This means that the amplitude of the first total voltage signal and the second total voltage signal is centered on the reference voltage, which facilitates the subsequent signal processing circuit 40 to perform signal processing on the first total voltage signal and the second total voltage signal, so as to obtain the capacitance change value of the detection capacitor 10 more accurately.

[0072] Reference Figure 3 and Figure 4 In one embodiment, the voltage cancellation output circuit includes a first switch, a second switch, a first voltage cancellation source, and a second voltage cancellation source;

[0073] The first switch is connected in series between the canceling capacitor and the first canceling voltage source. When the first switch is turned on, it controls the first canceling voltage source to be electrically connected to the canceling capacitor, so that the canceling capacitor outputs a first canceling signal to the capacitor-to-voltage circuit 30.

[0074] The second switch is connected in series between the canceling capacitor and the second canceling voltage source. When the second switch is turned on, it controls the second canceling voltage source to be electrically connected to the canceling capacitor, so that the canceling capacitor outputs a second canceling signal to the capacitor-to-voltage circuit 30.

[0075] Optionally, the coding driving circuit 20 includes a third switch, a fourth switch, a first coding voltage source, and a second coding voltage source;

[0076] The third switch is connected in series between the first coding voltage source and the capacitor-to-voltage circuit 30. The third switch is used to control the first coding voltage source and the capacitor-to-voltage circuit 30 to be electrically connected when the circuit is turned on, so as to output the first coding drive signal to the capacitor-to-voltage circuit 30.

[0077] The fourth switch is connected in series between the second coding voltage source and the capacitor-to-voltage circuit 30. When the fourth switch is turned on, it controls the second coding voltage source to be electrically connected to the capacitor-to-voltage circuit 30 so as to output the second coding drive signal to the capacitor-to-voltage circuit 30.

[0078] In another embodiment, the coding driving circuit 20 can also be implemented using a variable voltage source or a signal generation circuit. Different voltage sources are generated using the variable voltage source or signal generation circuit, which serve as the first coding voltage source and the second coding voltage source, respectively. The two voltage sources are set to be output periodically alternately. For example, the coding driving circuit 20 first outputs the first coding voltage source, then switches to output the second coding voltage source after 10 seconds, and switches again after 10 seconds. This periodic alternation of output allows the coding driving circuit 20 to periodically and alternately output the first coding driving signal and the second coding driving signal.

[0079] Similarly, it can be understood that the cancellation voltage output circuit can also be implemented using a variable voltage source or a signal generation circuit. Different voltage sources can be generated using the variable voltage source or signal generation circuit, which can be used as the first cancellation voltage source and the second cancellation voltage source respectively. The two voltage sources can be set to periodically alternately output. In this way, the cancellation voltage output circuit can periodically alternately output the first cancellation voltage source and the second cancellation voltage source to the cancellation capacitor.

[0080] Optionally, the capacitor-to-voltage circuit 30 includes an operational amplifier, a feedback capacitor, a fifth switch, and a sixth switch. The inverting input of the operational amplifier is connected to the detection capacitor 10, the non-inverting input of the operational amplifier is connected to the output of the coding drive circuit 20, the output of the operational amplifier is connected to the first terminal of the fifth switch, the second terminal of the fifth switch is connected to the receiving terminal of the signal processing circuit 40, the first terminal of the sixth switch is connected to the inverting input of the operational amplifier, the second terminal of the sixth switch is connected to the output of the operational amplifier, the first terminal of the feedback capacitor is connected to the inverting input of the operational amplifier, and the second terminal of the feedback capacitor is connected to the second terminal of the fifth switch.

[0081] In this embodiment, the capacitor-to-voltage circuit 30 is a single-ended structure. The positive input terminal of the operational amplifier is connected to the coding drive circuit 20 to receive the first coding drive signal and the second coding drive signal. The inverting input terminal of the operational amplifier is connected to the detection capacitor 10. In this way, the operational amplifier can output the corresponding first total voltage signal and second total voltage signal according to the first coding drive signal, the second coding drive signal and the capacitance value of the detection capacitor 10, that is, convert the capacitance of the detection capacitor 10 into a voltage value and output it.

[0082] It is understood that in some other embodiments, the capacitor-to-voltage circuit 30 can also be implemented using a differential structure. Similarly, when the capacitor-to-voltage circuit 30 is implemented using a differential structure, the signal processing circuit 40 can also be implemented using a differential structure. This will not be limited to one by one.

[0083] To better illustrate the inventive concept of this invention, the following combines existing technology and... Figure 3 and Figure 4 The working principle of this invention will be explained.

[0084] Reference Figure 3 , Figure 3 This is a circuit diagram of a prior art capacitance detection circuit, where C tp For the capacitance of the capacitive sensor, C c To compensate for the capacitance, the purpose is to avoid V OUT Saturation. Its working principle is as follows:

[0085] Reset phase: Switches S5 / S1 / S3 are on, switches S2 / S4 are off, V OUT =V CM .

[0086] Charge redistribution stage: Switches S5 / S1 / S3 are open, switches S2 / S4 are closed, V OUT The expression is:

[0087]

[0088] General setting V CM =V DD / 2, C tp =C c At this time, V OUT =V CM .

[0089] When the capacitance C of the capacitance sensor tp Change to C tp +ΔC tp hour,

[0090]

[0091] The signal quantity caused by the change in capacitance is:

[0092]

[0093] The above formula converts the change in capacitance into a change in voltage, and the change in voltage is proportional to the change in capacitance. This voltage is then converted into a digital value by an ADC and transmitted to the MCU for further processing and judgment.

[0094] The coding range is defined as C tp The peak-to-peak value of the voltage change, in existing technical solutions, is V. DD -V CM =V CM .

[0095] Reference Figure 3 and Figure 4 , Figure 3 This is a circuit diagram of one embodiment of the capacitance detection circuit of this application. Figure 4 The figure shows the switching timing diagram of the capacitance detection circuit of this application, which illustrates the timing of two complete operating cycles of the capacitance detection circuit.

[0096] During the time interval t0 to t1, switches RST1 / RST1' / K2 / K2' are turned on, and switches RST2 / K1 / K1' are turned off. The charges on each capacitor are as follows:

[0097] Q Ctp =V L C tp

[0098] Q Cc =(V L -V CN C C

[0099] Q Cf =(V L -V CM C f

[0100] Among them, V OUT =V CM .

[0101] During the time interval t1 to t2, switches RST1 / RST1' / K2 / K2' are open, and switches RST2 / K1 / K1' are closed. The charges on each capacitor are as follows:

[0102] Q Ctp =V H C tp

[0103] QCc =(V H -V CP C C

[0104] Q Cf =(V H -V OUT C f

[0105] According to the law of conservation of charge:

[0106] V L C tp +(V L -V CN C C +(V L -V Cm C f

[0107] =V H C tp +(V H -V CP C C +(V H -V OUT C f

[0108] Get V OUT The expression for the first voltage change signal is:

[0109]

[0110] If we let:

[0111] (V H -V L (C) tp +C f )+(V H -V L -V CP +V CN C C =0

[0112] Right now:

[0113]

[0114] At this time, V OUT =V CM .

[0115] When the capacitance C of the capacitance sensor tp Change to C tp +ΔC tp hour,

[0116]

[0117] The signal quantity caused by the change in capacitance is:

[0118]

[0119] During time intervals t2 to t3, switches RST1 / RST1' / K1 / K1' are turned on, and switches RST2 / K2 / K2' are turned off. The charges on each capacitor are as follows:

[0120] Q Ctp =V H C tp

[0121] Q Cc =(V H -V CP C C

[0122] Q Cf =(V H -V CM C f

[0123] Among them, V OUT =V CM .

[0124] During time intervals t3 to t4, switches RST1 / RST1' / K1 / K1' are open, and switches RST2 / K2 / K2' are closed. The charges on each capacitor are as follows:

[0125] Q Ctp =V L C tp

[0126] Q Cc =(V L -V CN C C

[0127] Q Cf =(V L -V OUT C f

[0128] According to the law of conservation of charge:

[0129] V H C tp +(V H -V CP C C +(V H -V CM C f

[0130] =V L C tp +(V L -V CN C C +(V L -V OUT C f

[0131] Get V OUT The expression for the second voltage change signal is:

[0132]

[0133] because

[0134]

[0135] Therefore, V OUT =V CM .

[0136] When the capacitance C of the capacitance sensor tp Change to C tp +ΔC tp hour,

[0137]

[0138] The signal quantity caused by the change in capacitance is:

[0139]

[0140] After the above operations, ΔV OUT The peak value is:

[0141]

[0142] The above formula converts the change in capacitance into a change in voltage, and this voltage change is directly proportional to the change in capacitance. This voltage is then converted into a digital value by an ADC and transmitted to the MCU for further processing. In the above derivation, V... H -V L This refers to the censorship range, see reference. Figure 4 Obviously V OUT The amplitude of V CM Centered on V CM The upper part represents the signal quantity generated when K1 is turned on, V CM The lower part represents the signal generated when K2 is turned on. The signal generated is doubled in this solution compared to the previous technology, thereby improving the sensitivity of the capacitance detection circuit in this solution.

[0143] also,

[0144]

[0145] As can be seen from the above formula, although C is added to the molecule f The amount of C, but C f Usually less than C tp From the denominator (V) of the above equation CP -V CN )-(V H -V L It can be seen that if V is increased... CP -V CN The value of V, or decrease V H -V L If the value of is increased, the value of the denominator can be increased, thereby increasing the compensation capacitor C. C The value decreases, meaning that for the same C in existing capacitance detection circuits... tp The required cancellation capacitor C in this application C The value will decrease.

[0146] As can be seen from the above analysis, in the technical solution of this invention, compared with the existing capacitance detection circuit, this invention can increase the final acquired signal amount under the same coding amplitude, thereby improving the sensitivity of capacitance detection. At the same time, this invention can also reduce the capacitance value of the cancellation capacitor by adjusting the coding voltage and cancellation voltage, thereby reducing the volume of the cancellation capacitor, effectively reducing the chip area, reducing the overall volume of the capacitance detection circuit, and improving the practicality and stability of the capacitance detection circuit.

[0147] In the technical solution of this invention, the switching transistors mentioned above can all be implemented using electronic switches such as MOSFETs and IGBTs. The invention process is specifically implemented based on controller control. The switch control in the above process can be controlled by a specially set controller for controlling the coding drive circuit 20 and the voltage cancellation circuit 50, or it can be integrated and controlled by a processor that processes the signal quantity. No specific limitation is made here.

[0148] Reference Figures 1 to 3 In one embodiment, the signal processing circuit 40 includes:

[0149] An analog-to-digital converter (ADC) is provided, the input of which is connected to the output of the programmable gain amplifier. The ADC is used to convert the total voltage signal output by the capacitor-to-voltage circuit 30 into an analog-to-digital signal and then output it.

[0150] A signal processor, the input of which is connected to the output of the analog-to-digital converter, is used to process the first total voltage signal and the second total voltage signal output by the analog-to-digital converter to obtain the capacitance change of the detection capacitor 10.

[0151] In this embodiment, the signal processing circuit 40 can be implemented using an analog-to-digital converter (ADC) and a signal processor. The ADC is used to convert the analog signal output by the capacitor-to-voltage circuit 30 into a digital signal and then output it to the signal processor. The signal processor can be implemented using a microprocessor such as a microcontroller, FPGA, or CPLD. The signal processor can obtain the capacitance change of the detection capacitor 10 by means of table lookup, quadrature demodulation, and fast Fourier transform based on the first voltage change signal and the second voltage change signal output by the capacitor-to-voltage circuit 30.

[0152] It is understood that the signal processor can also be used to control the coding drive circuit 20, the cancellation voltage output circuit, and the reference circuit 60, so that the coding drive circuit 20 periodically and alternately outputs the first coding drive signal and the second coding drive signal, so that the cancellation voltage output circuit can periodically and alternately output the first cancellation voltage source and the second cancellation voltage source to the cancellation capacitor, and so that the coding drive signal output by the coding drive circuit 20 corresponds to the cancellation voltage source output by the cancellation voltage output circuit, thereby realizing all the technical solutions of all the above embodiments.

[0153] Alternatively, the signal processor can also be used as a signal generation circuit to generate different voltage sources such as a first coding voltage source, a second coding voltage source, a first cancellation voltage source, a second cancellation voltage source, and a reference voltage source. This integrates the coding drive circuit 20, the cancellation voltage output circuit, and the reference circuit 60 onto the same chip. By using the integrated chip, different voltage sources or signals can be output and controlled, reducing the number of switching transistors and thus reducing the overall size of the capacitance detection circuit of the present invention, making the capacitance detection circuit more compact and convenient.

[0154] The present invention also proposes a touch chip, which includes the above-described capacitance detection circuit. The specific structure of the capacitance detection circuit is as described in the above embodiments. Since the present touch chip adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0155] The present invention also proposes an electronic device, wherein the touch chip includes the touch chip described above, or includes the capacitance detection circuit described above. The specific structure of the capacitance detection circuit and the touch chip is as described in the above embodiments. Since the electronic device adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0156] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A capacitance detection circuit, characterized in that, The capacitance detection circuit includes: A detection capacitor is used to detect external sensing signals and output the corresponding capacitance value. A coding driving circuit is used to periodically and alternately output a first coding driving signal and a second coding driving signal. A capacitor-to-voltage circuit is provided, wherein a first input terminal of the capacitor-to-voltage circuit is connected to the detection capacitor, and a second input terminal of the capacitor-to-voltage circuit is connected to the output terminal of the coding drive circuit. The capacitor-to-voltage circuit is used to output a corresponding first total voltage signal according to the capacitance value of the detection capacitor and the first coding drive signal when the coding drive circuit outputs a first coding drive signal, and to output a corresponding second total voltage signal according to the capacitance value of the detection capacitor and the second coding drive signal when the coding drive circuit outputs a second coding drive signal. The signal processing circuit has its receiving end connected to the output end of the capacitor-to-voltage circuit. The signal processing circuit is also used to process the first total voltage signal and the second total voltage signal to obtain the capacitance change of the detection capacitor. The capacitance detection circuit further includes: A voltage cancellation circuit, connected to the first input terminal of the capacitor-to-voltage conversion circuit, is configured to output a first cancellation signal to the capacitor-to-voltage conversion circuit when the coding drive circuit outputs a first coding drive signal, so that the capacitor-to-voltage conversion circuit cancels the base voltage signal according to the first cancellation signal, converts the first total voltage signal into a corresponding first voltage change signal, and then outputs it; and... The voltage cancellation circuit is also used to output a second cancellation signal to the capacitor-to-voltage circuit when the coding drive circuit outputs a second coding drive signal, so that the capacitor-to-voltage circuit cancels the basic voltage signal according to the second cancellation signal, converts the second total voltage signal into a corresponding second voltage change signal, and then outputs it. The basic voltage signal is the voltage signal that characterizes the basic capacitance value of the detection capacitor in the first total voltage signal and the second total voltage signal; The signal processing circuit is also used to process the first voltage change signal and the second voltage change signal to obtain the change in the detection capacitor.

2. The capacitance detection circuit as described in claim 1, characterized in that, The voltage cancellation circuit includes: A cancelling capacitor, the first terminal of which is connected to the first input terminal of the capacitor-to-voltage circuit; A cancellation voltage output circuit, the output terminal of which is connected to the second terminal of the cancellation capacitor, is used to output a first cancellation voltage to the cancellation capacitor when the coding drive circuit outputs a first coding drive signal, so that the cancellation capacitor outputs a first cancellation signal to the capacitor-to-voltage conversion circuit; and... The offset voltage output circuit is also used to output a second offset voltage to the offset capacitor when the coding drive circuit outputs a second coding drive signal, so that the offset capacitor outputs a second offset signal to the capacitor-to-voltage circuit.

3. The capacitance detection circuit as described in claim 2, characterized in that, The voltage cancellation output circuit includes a first switch, a second switch, a first voltage cancellation source, and a second voltage cancellation source; The first switch is connected in series between the canceling capacitor and the first canceling voltage source. When the first switch is turned on, it controls the first canceling voltage source to be electrically connected to the canceling capacitor, so that the canceling capacitor outputs a first canceling signal to the capacitor-to-voltage circuit. The second switch is connected in series between the canceling capacitor and the second canceling voltage source. When the second switch is turned on, it controls the second canceling voltage source to be electrically connected to the canceling capacitor, so that the canceling capacitor outputs a second canceling signal to the capacitor-to-voltage circuit.

4. The capacitance detection circuit as described in claim 1, characterized in that, The capacitance detection circuit further includes: A reference circuit is provided, the output of which is connected to the output of the capacitor-to-voltage circuit. The reference circuit is used to output a reference voltage as a reference value for the first total voltage signal and the second total voltage signal.

5. The capacitance detection circuit as described in claim 1, characterized in that, The coding driving circuit includes a third switch, a fourth switch, a first coding voltage source, and a second coding voltage source. The third switch is connected in series between the first coding voltage source and the capacitor-to-voltage circuit. The third switch is used to control the first coding voltage source and the capacitor-to-voltage circuit to be electrically connected when the circuit is turned on, so as to output the first coding drive signal to the capacitor-to-voltage circuit. The fourth switch is connected in series between the second coding voltage source and the capacitor-to-voltage circuit. When the fourth switch is turned on, it controls the second coding voltage source to be electrically connected to the capacitor-to-voltage circuit so as to output the second coding drive signal to the capacitor-to-voltage circuit.

6. The capacitance detection circuit as described in claim 1, characterized in that, The capacitor-to-voltage conversion circuit includes an operational amplifier, a feedback capacitor, a fifth switch, and a sixth switch. The inverting input of the operational amplifier is connected to the detection capacitor, the non-inverting input of the operational amplifier is connected to the output of the coding drive circuit, the output of the operational amplifier is connected to the first terminal of the fifth switch, the second terminal of the fifth switch is connected to the receiving terminal of the signal processing circuit, the first terminal of the sixth switch is connected to the inverting input of the operational amplifier, the second terminal of the sixth switch is connected to the output of the operational amplifier, the first terminal of the feedback capacitor is connected to the inverting input of the operational amplifier, and the second terminal of the feedback capacitor is connected to the second terminal of the fifth switch.

7. The capacitance detection circuit as described in claim 1, characterized in that, The signal processing circuit includes: An analog-to-digital converter (ADC) is provided, wherein the input terminal of the ADC is connected to the output terminal of the capacitor-to-voltage circuit, and the ADC is used to convert the total voltage signal output by the capacitor-to-voltage circuit into an analog-to-digital signal before outputting it. A signal processor, the input of which is connected to the output of the analog-to-digital converter, is used to process the first total voltage signal and the second total voltage signal output by the analog-to-digital converter to obtain the capacitance change of the detection capacitor.

8. A touch chip, characterized in that, Includes the capacitance detection circuit as described in any one of claims 1-7.

9. An electronic device, characterized in that, It includes the touch chip as described in claim 8; or, it includes the capacitance detection circuit as described in any one of claims 1-7.

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