WO2022087974A1

WO2022087974A1 - Capacitance measurement circuit, touch chip, and parameter adjustment method for capacitance measurement circuit

Info

Publication number: WO2022087974A1
Application number: PCT/CN2020/124899
Authority: WO
Inventors: 张冠军; 蒋宏
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2020-10-29
Filing date: 2020-10-29
Publication date: 2022-05-05

Abstract

The present application provides a capacitance measurement circuit, a touch chip, and a parameter adjustment method for the capacitance measurement circuit, capable of improving the sensitivity of capacitance measurement. The capacitance measurement circuit comprises: a first driving circuit connected to a capacitor to be measured and used for outputting a first driving signal; a cancellation circuit comprising a cancellation capacitor and a second driving circuit, the second driving circuit being connected to the cancellation capacitor and used for outputting a second driving signal; and an amplification circuit connected to the capacitor to be measured and the cancellation capacitor and used for outputting a voltage signal according to a capacitance signal of the capacitor to be measured and a capacitance signal of the cancellation capacitor, the voltage signal being used for determining, relative to a basic capacitance, the capacitance variation of the capacitance of the capacitor to be measured, wherein the capacitance of the cancellation capacitor and parameters of the second driving signal are configured to minimize, in the case that the capacitance of the capacitor to be measured does not change relative to the basic capacitance, the voltage signal outputted by the amplification circuit to cancel the basic capacitance of the capacitor to be measured.

Description

Capacitance detection circuit, touch chip and parameter adjustment method of capacitance detection circuit

technical field

Embodiments of the present application relate to the field of capacitance detection, and more particularly, to a capacitance detection circuit, a touch control chip, and a parameter adjustment method for a capacitance detection circuit.

Background technique

Capacitive sensors are widely used in electronic products for touch detection. When no finger touches or approaches the detection electrode, the capacitance of the detection electrode is equal to the basic capacitance (or initial capacitance); when a finger approaches or touches the detection electrode, the capacitance of the detection electrode will change relative to the basic capacitance. The capacitance change of the detection electrode relative to the basic capacitance can obtain the information of the finger approaching or touching the detection electrode, so as to judge the user's operation. However, since the basic capacitance is often relatively large, it will occupy a limited dynamic range of the circuit, thus reducing the sensitivity of capacitance detection.

SUMMARY OF THE INVENTION

Embodiments of the present application provide a capacitance detection circuit, a touch control chip, and a parameter adjustment method for the capacitance detection circuit, which can improve the sensitivity of capacitance detection.

In a first aspect, a capacitance detection circuit is provided, including:

a first drive circuit, connected to the capacitor to be tested, for outputting a first drive signal to the capacitor to be tested, wherein the capacitance of the capacitor to be tested is the mutual capacitance between two detection electrodes in the touch screen;

a canceling circuit, including a canceling capacitor and a second driving circuit, the second driving circuit is connected to the canceling capacitor, and is used for outputting a second driving signal to the canceling capacitor; and,

an amplifying circuit, connected to the capacitor to be measured and the cancellation capacitor, and used to output a voltage signal according to the capacitance signal of the capacitor to be measured and the capacitance signal of the cancellation capacitor, wherein the voltage signal is used to determine the The capacitance change of the capacitance of the capacitor to be measured relative to the basic capacitance;

Wherein, the capacitance of the canceling capacitor and the parameters of the second driving signal are configured such that under the condition that the capacitance of the capacitor to be measured does not change relative to the basic capacitance, the output of the amplifying circuit The voltage signal is minimized to cancel the base capacitance of the capacitor under test.

The capacitance detection circuit in the embodiment of the present application can effectively cancel the basic capacitance of the capacitor to be measured through the cancellation circuit, so that the voltage signal output by the amplifying circuit only reflects the capacitance change of the capacitor to be measured, so that the basic capacitance is used in the capacitance detection circuit. The proportion of the dynamic range occupied in the CCD is reduced, the magnification of the amplifying circuit is increased, the sensitivity of the capacitance detection is improved, and the detection performance of the capacitance detection circuit is improved. In addition, in the embodiment of the present application, the influence of parasitic parameters such as screen impedance on capacitance detection in actual situations is considered, and by configuring the second driving signal and the cancellation capacitor in the capacitance detection circuit, not only the basic capacitance can be cancelled, but also the basic capacitance can be cancelled as much as possible. The influence of screen impedance, etc. on capacitive detection is reduced.

Moreover, a second driving circuit is provided in the cancellation circuit, and under the action of the second driving signal output by the second driving circuit, the basic capacitance of the capacitor to be measured is cancelled by the cancellation capacitor, so there is no need to set up a large number of switches to complicate the capacitance detection process The timing control is simpler, and the circuit structure is simpler.

In a possible implementation manner, the parameters of the second drive signal include at least one of the following: a waveform of the second drive signal, an amplitude of the second drive signal, and the second drive signal phase.

In a possible implementation manner, the waveform of the second driving signal is the same as the waveform of the first driving signal, the amplitude of the second driving signal is the same as the amplitude of the first driving signal, and the first driving signal has the same amplitude. The phase difference between the phases of the two driving signals and the phase of the first driving signal is 170° to 190°.

In this way, when the waveform of the second driving signal is the same as the waveform of the first driving signal, and the amplitude of the second driving signal is the same as that of the first driving signal, the phase of the second driving signal can be configured to be the same as that of the first driving signal. The phases of the driving signals are opposite, and then the capacitance of the cancellation capacitor and the phase of the second driving signal are scanned in turn, so as to efficiently find the capacitance value and phase value corresponding to the minimum voltage signal output by the amplifier circuit.

In a possible implementation manner, the cancellation circuit further includes a cancellation resistor connected to the cancellation capacitor.

In a possible implementation manner, the canceling resistance is used to cancel the screen body impedance of the touch screen.

Since the traces and devices in the screen will form a certain equivalent impedance, by setting the offset resistor, it can be used to offset the screen impedance of the touch screen. By configuring the offset resistor, the effect of capacitance offset is further optimized. .

In a possible implementation manner, the cancellation resistor is configured to make the voltage signal output by the amplifying circuit reach a minimum value under the condition that the capacitance of the capacitor to be measured does not change with respect to the base capacitance .

In a possible implementation manner, the amplifying circuit includes a programmable gain amplifier PGA, and a feedback resistor is connected between each input end of the PGA and a corresponding output end.

In a possible implementation manner, the capacitance detection circuit further includes: a filter circuit, connected to the amplifying circuit, for filtering the voltage signal output by the amplifying circuit; an analog-to-digital conversion circuit, connected to the amplifying circuit. the filter circuit is connected to convert the filtered voltage signal into a digital signal; and a digital processing module is connected to the filter circuit for processing the digital signal to obtain the capacitance change quantity.

In a second aspect, a touch control chip is provided, including the first aspect and the capacitance detection circuit in any possible implementation manner of the first aspect.

In a third aspect, a method for adjusting parameters of a capacitance detection circuit is provided, wherein the capacitance detection circuit includes a first drive circuit, an offset circuit and an amplifier circuit, the first drive circuit is connected to the capacitor to be measured and is used to send the capacitor to the to-be-measured capacitor. The measuring capacitor outputs a first driving signal, wherein the capacitance of the capacitor to be measured is the mutual capacitance between two detection electrodes in the touch screen, and the canceling circuit includes a canceling capacitor and a second driving circuit, and the second driving circuit connected to the cancellation capacitor and used for outputting a second driving signal to the cancellation capacitor, the amplifying circuit is connected to the capacitor to be tested and the cancellation capacitor and used for outputting a second drive signal according to the capacitance signal of the capacitor to be tested and the cancellation The capacitance signal of the capacitor outputs a voltage signal, the voltage signal is used to determine the capacitance change of the capacitance of the capacitor to be measured relative to the base capacitance, and the method is used to configure the capacitance of the cancellation capacitor and the second capacitance parameters of the drive signal to cancel the base capacitance of the capacitor under test, wherein the method includes:

Under the condition that the capacitance of the capacitor under test does not change relative to the basic capacitance, the waveform of the second driving signal is configured to be the same as the waveform of the first driving signal, and the amplitude of the second driving signal is the same as that of the first driving signal. The amplitude of the first drive signal is the same, and the phase of the second drive signal is opposite to the phase of the first drive signal;

Scan the capacitance of the cancellation capacitor to obtain a variation curve of the voltage signal output by the amplifying circuit with the capacitance of the cancellation capacitor, and configure the capacitance of the cancellation capacitor to be the smallest according to the variation curve. The capacitance corresponding to the voltage signal;

The phase of the second drive signal is scanned to obtain a change curve of the voltage signal output by the amplifier circuit with the phase of the second drive signal, and the second drive signal is calculated according to the change curve. The phase is adjusted to the phase corresponding to the minimum voltage signal.

In a possible implementation manner, the method further includes: scanning the capacitance of the cancellation capacitor to obtain a variation curve of the voltage signal output by the amplifying circuit with the capacitance of the cancellation capacitor, and according to the The change curve adjusts the capacitance of the cancellation capacitor to the smallest capacitance corresponding to the voltage signal.

In a possible implementation manner, the cancellation circuit further includes a cancellation resistor connected to the cancellation capacitor, and the method further includes: scanning the resistance value of the cancellation resistor to obtain all the output values of the amplifying circuit. The voltage signal changes curve with the resistance value of the cancellation resistor, and according to the change curve, the resistance value of the cancellation resistor is configured to the minimum resistance value corresponding to the voltage signal, wherein the cancellation resistance before scanning The resistance value is configured as 0.

Description of drawings

FIG. 1 is a schematic diagram of the principle of touch detection.

FIG. 2 is a schematic diagram of a conventional capacitance detection circuit.

FIG. 3 is a schematic diagram of a capacitance detection circuit according to an embodiment of the present application.

FIG. 4 is a schematic flowchart of a method for adjusting parameters of the capacitance detection circuit shown in FIG. 3 according to an embodiment of the present application.

FIG. 5 is a schematic diagram of the variation curve of the cancellation efficiency with the cancellation capacitance obtained based on the method shown in FIG. 4 .

FIG. 6 is a schematic diagram of a variation curve of the cancellation efficiency with the phase of the second driving signal obtained based on the method shown in FIG. 4 .

FIG. 7 is a schematic diagram of a capacitance detection circuit according to another embodiment of the present application.

FIG. 8 is a schematic flowchart of a method for adjusting parameters of the capacitance detection circuit shown in FIG. 7 according to an embodiment of the present application.

FIG. 9 is a possible specific implementation based on the capacitance detection circuit shown in FIG. 3 .

FIG. 10 is a possible specific implementation based on the capacitance detection circuit shown in FIG. 7 .

Detailed ways

The technical solutions in the present application will be described below with reference to the accompanying drawings.

First, a schematic diagram of a possible application scenario of the capacitance detection circuit of the embodiment of the present application is described with reference to FIG. 1 .

Figure 1 shows the horizontal and vertical two-layer channels in the touch screen. A capacitive touch system using this pattern can usually use both self-capacitance and mutual-capacitance detection methods at the same time. When performing self-capacitance detection, the touch chip will scan the change of the self-capacitance to ground of each horizontal channel and vertical channel. When a finger approaches or touches, the self-capacitance of the channel near the finger becomes larger. For example, as shown in FIG. 1, the finger and its nearby lateral channel C _RXN-1 will generate capacitance Cs, and the finger and its nearby vertical channel C _TX1 will generate capacitance Cd. Since the human body is a conductor and is connected to the ground, the self-capacitance of the channel touched or approached by the finger will change, and the touch chip can obtain the touch information of the finger according to the detected change of the self-capacitance. When the mutual capacitance detection is performed, the change of the mutual capacitance between the horizontal channel and the vertical channel is detected. For example, as shown in Figure 1, mutual capacitance will be generated between the horizontal channel C _RXN-1 and the vertical channel C _TX1 near the finger. touch information. Here, the horizontal channel in FIG. 1 is referred to as an RX channel, and the vertical channel is referred to as a TX channel, and the horizontal and vertical channels in the touch screen may also be referred to as detection electrodes or sensors.

Taking mutual capacitance detection as an example, the capacitance detection circuit 200 shown in FIG. 2 is used to detect the mutual capacitance between the TX channel and the RX channel, that is, the capacitor to be tested 100 formed between the TX channel and the RX channel. The touch chip sends the drive signal V _TX to the TX channel, and outputs the corresponding detection signal from the RX channel. One end of the amplifying circuit is connected to the voltage V _CMI , and the other end is connected to the RX channel to receive the detection signal from the RX channel and output the voltage signal V _OUT . The voltage signal V _OUT can be used to determine the capacitance of the capacitor 100 under test. The capacitance of the capacitor to be measured 100 includes a base capacitance C _X and a capacitance change ΔC _{X relative to the base capacitance C X} _. Wherein, when there is no finger touching or approaching, the detected capacitance of the capacitor under test 100 is the basic capacitance C _X ; when there is a finger approaching or touching, the capacitance of the capacitor under test 100 will be higher than the basic capacitance C X relative to the basic capacitance C _X Changes occur on the basis of C _X , so the detected capacitance of the capacitor to be measured 100 includes the basic capacitance C _X and the capacitance variation ΔC _X , wherein the capacitance variation ΔC _X actually reflects the user's touch information. Because the basic capacitance C _X is often relatively large, it will occupy a limited dynamic range of the circuit, that is, the basic capacitance C _X occupies a large proportion of the dynamic range of the capacitance detection circuit, thus reducing the sensitivity of capacitance detection.

Therefore, the present application provides a capacitance detection circuit, which can improve the sensitivity of capacitance detection.

FIG. 3 is a schematic diagram of a capacitance detection circuit according to an embodiment of the present application. The capacitance detection circuit 300 is used to detect the capacitance change of the capacitor 100 to be measured. The capacitance of the capacitor to be measured 100 is the mutual capacitance between two detection electrodes in the touch screen. That is, the capacitance detection circuit 300 is used for mutual capacitance detection. As shown in FIG. 3 , the capacitance detection circuit 300 includes a first driving circuit 310 , a cancellation circuit 320 and an amplifying circuit 330 .

The first driving circuit 310 is connected to the capacitor under test 100 for outputting the first drive signal V _TX to the capacitor under test 100 .

The cancellation circuit 320 is used to cancel the base capacitance C _X of the capacitor under test 100 . The cancellation circuit 320 includes a cancellation capacitor 321 and a second driving circuit 322 , wherein the second driving circuit 322 is connected to the cancellation capacitor 321 for outputting the second driving signal V _Cancel to the cancellation capacitor 321 .

The amplifying circuit 330 is connected to the capacitor under test 100 and the cancellation capacitor 321, and is used for receiving the first capacitance signal of the capacitor under test 100 and the second capacitance signal of the canceling capacitor 321, and outputting according to the first capacitance signal and the second capacitance signal voltage signal V _OUT . The voltage signal V _OUT is used to determine the capacitance change ΔC _{X of the capacitance of the capacitor under test 100 relative to the base capacitance C X} _.

Usually, for example, in the case of single-finger touch, the ratio of the capacitance change ΔC _X to the base capacitance C _X is about 1:10, and the base capacitance C _X will occupy most of the dynamic range of the capacitance detection circuit 300, so that the amplification circuit The magnification of the 330 is limited, which affects the sensitivity of capacitive detection.

In the embodiment of the present application, since the cancellation circuit 320 is used to cancel the base capacitance C _X of the capacitor under test 100 , the voltage signal V _OUT output by the amplifier circuit 330 and the capacitance of the capacitor under test 100 relative to the base capacitance C _X are changed. The capacitance change amount _{ΔC X} _can be determined by the voltage signal V _OUT output by the amplifying circuit 330 , thereby increasing the amplification factor of the amplifying circuit and improving the sensitivity of capacitance detection.

The cancellation circuit 320 is provided with a second driving circuit 322 , and under the action of the second driving signal output by the second driving circuit 322 , the basic capacitance C _X of the capacitor under test 100 is cancelled by the cancellation capacitor 321 . In the process of outputting the driving signal from the first driving circuit 310 and the second driving circuit 322, the cancellation capacitor 321 can complete the cancellation of the basic capacitance C _X of the capacitor under test 100. Therefore, there is no need to set up a large number of switches to complicate the capacitance detection process. Sequence control, the circuit structure is simpler and easier to implement.

Specifically, when the capacitance of the capacitor under test 100 does not change relative to the base capacitance C _X , that is, ΔC _X =0, for example, when there is no finger touch, the capacitance of the capacitor under test 100 is equal to the base capacitance C _X . The capacitance C _C of the cancellation capacitor 321 is configured to be equal to the base capacitance C _X , and the second driving signal and the first driving signal are configured to have the same waveform, equal amplitude, and opposite phase. The first drive circuit 310 outputs a first drive signal to the capacitor under test 100, so that a corresponding current signal is generated on the branch where the capacitor under test 100 is located, and the second drive circuit 322 outputs a second drive signal to the cancellation capacitor 321, so that the cancellation capacitor 321 The corresponding current signal is generated on the branch. Therefore, when the current signal of the branch where the capacitor to be measured 100 is located and the current signal of the branch where the cancellation capacitor 321 is located flow to the amplifier circuit 330 at the same time, the mutual cancellation between the two current signals can make the voltage signal V output by the amplifier circuit V _OUT is basically 0. When the capacitance of the capacitor under test 100 changes relative to the base capacitance C _X , that is, ΔC _X ≠ 0, for example, when there is a finger touch, the capacitance of the capacitor under test 100 includes the base capacitance C _X and the capacitance change amount ΔC _X , since the configuration of the canceling capacitor 321 and the second driving signal can cancel the part of the current signal corresponding to the base capacitor C _X , the current signal flowing to the amplifying circuit 330 only includes the part of the current signal corresponding to the capacitance change ΔC _X . In this way, through the voltage signal V _OUT output by the amplifying circuit 330 , the capacitance change amount ΔC _X can be determined, and the touch information of the finger can be determined according to the capacitance change amount ΔC _X . Since the base capacitance C _X is canceled, the amplification factor of the amplifying circuit 330 can be increased, thereby improving the sensitivity of capacitance detection.

In this embodiment of the present application, the waveform of the second driving signal V _Cancel is the same as the waveform of the first driving signal V _TX , for example, both are sine waves, cosine waves, square waves, or triangle waves. And, in an ideal situation, when the capacitance C _C of the cancellation capacitor 321 is configured to be equal to the basic capacitance C _X , that is, C _C =C _X , and the second driving signal V _Cancel is configured to have the same amplitude and opposite phase as the first driving signal V _TX , the cancellation efficiency of the cancellation circuit 320 can reach 100%, that is, the basic capacitance C _X can be completely cancelled.

However, in practical applications, due to the influence of parasitic parameters such as the screen impedance of the touch screen, the ideal situation cannot be achieved. Therefore, in the embodiment of the present application, it is also necessary to offset the capacitance C _C of the capacitor 321 and the parameters of the second driving circuit 322 The adjustment is made to reduce the influence of the screen impedance and the like on the capacitance detection, so that the cancellation circuit 320 can achieve the highest cancellation efficiency.

Wherein, the capacitance C _C of the canceling capacitor 321 in the canceling circuit 320 and the parameters of the second driving circuit 322 are configured such that when the capacitance of the capacitor under test 100 does not change relative to the base capacitance C _X , that is, ΔC _X =0 Then, the voltage signal V _OUT output by the amplifying circuit 330 reaches a minimum value to cancel the base capacitance C _X of the capacitor under test 100 . Ideally, in theory, V _OUT can reach 0; but in practical applications, when V _OUT reaches the minimum, that is, it is closest to 0, it can be considered that the cancellation circuit 320 has achieved the highest cancellation efficiency, that is, it can cancel most of the basic capacitance C. _X .

In practical applications, not only the capacitance C _C of the cancellation capacitor 321 can be adjusted, but also the parameters of the second driving signal V _Cancel output by the second driving circuit 322 can be adjusted to adapt to different types of touch screens and different capacitances Detection encoding, etc. The parameters of the second drive signal V _Cancel include, for example, at least one of the following: the waveform of the second drive signal V _Cancel , the amplitude of the second drive signal V _Cancel , and the phase of the second drive signal V _Cancel . Under the same conditions, for example, when there is no finger touch, find the optimal parameter configuration until the voltage signal V _OUT output by the amplifying circuit 330 is minimized, so as to cancel the basic capacitance C _X as much as possible.

It should be understood that, in the embodiment of the present application, the described offsetting of the basic capacitance C _X of the capacitor under test 100 includes partially canceling the basic capacitance C _X or completely canceling the basic capacitance C _X . Wherein, when the voltage signal V _OUT is the smallest, the cancellation efficiency of the cancellation circuit 320 is the highest. In an ideal situation, the cancellation efficiency when V _OUT =0 is 100%, and the basic capacitance C _X of the capacitor under test 100 is completely cancelled.

Here, the cancellation efficiency of the cancellation circuit 320 is: the difference between the voltage signal V1 corresponding to the capacitance signal of the capacitor under test 100 and the voltage signal corresponding to the capacitance signal V2 of the cancellation capacitor 321, and the ratio between the voltage signal V1, that is, |V1-V2|/V1. It can be understood that the voltage signal V1 is the voltage signal output by the amplifier circuit 330 when the base capacitor C _X is not cancelled by the cancellation circuit 320 , such as the voltage signal output by the amplifier circuit shown in FIG. The voltage signal output by the amplifying circuit 330 when C _X is, for example, the voltage signal output by the amplifying circuit 330 shown in FIG. 3 .

In a preferred implementation, the parameter configuration of the second drive signal V _Cancel satisfies at least one of the following conditions: the waveform of the second drive signal V _Cancel is the same as the waveform of the first drive signal V _TX , and the second drive signal V Cancel has the same waveform as the first drive signal V TX. The amplitude of the signal V _Cancel is the same as the amplitude of the first driving signal V _TX , and the phase difference between the phase of the second driving signal V _Cancel and the phase of the first driving signal V _TX is within a preset range, for example, the phase difference is within 170° to 190°, in other words, the phase of the second drive signal V _Cancel is within ±10° of the opposite phase of the phase of the first drive signal V _TX .

In this way, when the waveform of the second driving signal V _Cancel is the same as the waveform of the first driving signal V _TX , and the amplitude of the second driving signal V _Cancel is the same as that of the first driving signal V _TX , the second driving signal The phase of V _Cancel is configured to be opposite to the phase of the first driving signal V _TX , and then the capacitance C _C of the cancellation capacitor 321 and the phase of the second driving signal V _Cancel are sequentially scanned, so that the voltage signal V _OUT can be efficiently found to reach the maximum Hour corresponds to the _CC value and the phase value of V _Cancel .

The capacitance C _C of the cancellation capacitor 321 can be configured to be between 1 pF and 10 pF, for example.

For example, the parameter adjustment method 400 of the capacitance detection circuit according to the embodiment of the present application is shown in FIG. 4 . The method 400 can be applied to, for example, the capacitance detection circuit 300 shown in the aforementioned FIG. 3 . The method 400 is used to configure the capacitance C _C of the cancellation capacitor 321 in the capacitance detection circuit 300 and the parameters of the second driving signal V _Cancel to cancel the base capacitance C _X of the capacitor under test 100 . As shown in FIG. 4, method 400 includes the following steps.

In step 410, the waveform of the second driving signal V _Cancel is configured to be the same as the waveform of the first driving signal V _TX , the amplitude of the second driving signal V _Cancel is the same as the amplitude of the first driving signal V _TX , and the second driving signal V The phase of _Cancel is opposite to that of the first driving signal V _TX .

In step 420, the capacitance C _C of the cancellation capacitor 321 is scanned to obtain a variation curve of the voltage signal V _OUT output by the amplifying circuit 330 with the capacitance C _C of the cancellation capacitor 321, and the capacitance C of the cancellation capacitor 321 is calculated according to the variation curve. _C is configured as the capacitance corresponding to the smallest voltage signal V _OUT .

In step 430, the phase of the second drive signal V _Cancel is scanned to obtain a change curve of the voltage signal V _OUT output by the amplifier circuit 330 with the phase of the second drive signal V _Cancel , and the second drive signal is converted into the second drive signal according to the change curve. The phase of V _Cancel is adjusted to the phase corresponding to the smallest voltage signal V _OUT .

Through the method 400 shown in FIG. 4 , the optimal size of the capacitance C _C of the cancellation capacitor 321 and the optimal size of the phase of the second driving signal V _Cancel can be obtained, so that the cancellation efficiency of the cancellation circuit 320 is the highest.

For example, as shown in FIG. 5, for step 420, the variation of the cancellation efficiency with the pair capacitance C _C can be obtained. When the voltage signal V _OUT output by the amplifier circuit 330 reaches the minimum value, the cancellation efficiency of the cancellation circuit 320 is the highest, which can reach nearly 70%. Therefore, based on the variation curve shown in Figure 5, the capacitance _CC can be configured to be equal to 32pF. In practice, the size of the final configured capacitance Cc varies in the vicinity of the base capacitance _Cx .

For another example, as shown in FIG. 6 , for step 430 , the variation of the cancellation efficiency with the phase of the second driving signal V _Cancel can be obtained. When the voltage signal V _OUT output by the amplifier circuit 330 reaches the minimum, the cancellation efficiency of the cancellation circuit 320 is the highest, which can reach more than 80%. Therefore, based on the change curve shown in FIG. 6 , the phase of the second driving signal V _Cancel can be adjusted to 7.2°.

Since the phase of the second drive signal V _Cancel is configured to be opposite to the phase of the first drive signal V _TX in step 410 , in step 430 , the opposite phase of the phase of the first drive signal V _TX is used as a reference, and the opposite phase is near the opposite phase. The phase of the second drive signal V _Cancel is scanned.

Of course, if the basic capacitance C _X of the capacitor under test 100 can be estimated in advance, then in step 410 , the capacitance C _C of the cancellation capacitor 321 can also be configured to be equal to the basic capacitance C _X , so that in step 420, the basic capacitance C _X is taken as Reference, scan capacitance C _C around C _X.

The above-mentioned scanning refers to the process of sequentially adjusting the scanned parameters to different values.

For example, when scanning the capacitance C _C of the cancellation capacitor 321 , the capacitance C _C of the cancellation capacitor 321 is sequentially adjusted to be equal to different values, so as to obtain the value of the voltage signal V _OUT corresponding to the different values. Wherein, at the beginning of scanning, for example, the initial value of C _C may be set equal to C _X .

For another example, when scanning the phases of the second driving signal V _Cancel , the phases of the second driving signal V _Cancel are sequentially adjusted to be equal to different phase values to obtain the voltage signal V _OUT values corresponding to the different phase values. Wherein, at the beginning of scanning, the initial value of the phase of the second driving signal V _Cancel is set to the opposite phase of the first driving signal V _TX .

Optionally, after step 430 , step 420 may also be performed again to further correct the capacitance C _C of the cancellation capacitor 321 .

In this embodiment of the present application, as shown in FIG. 7 , the cancellation circuit 320 may further include a cancellation resistor 323 connected to the cancellation capacitor 321 . Since the traces and devices in the screen body will form a certain equivalent impedance, the offset resistance 323 can be used to offset the screen body impedance of the touch screen. By configuring the cancellation resistor 323, the effect of capacitance cancellation is further optimized, so that the capacitance detection circuit 300 still has a good detection effect under non-ideal conditions.

The resistance value RC of the cancellation resistor 323 can be configured to be, for example, between _0kΩ and 10kΩ.

At this time, the parameters of the capacitance detection circuit 300 can be adjusted by the method shown in FIG. 8 . As shown in FIG. 8 , the parameter adjustment method 800 of the capacitance detection circuit according to the embodiment of the present application can be applied, for example, to the capacitance detection circuit 300 shown in the foregoing FIG. 7 . As shown in FIG. 8, method 800 includes the following steps.

In step 810, the waveform of the second driving signal V _Cancel is configured to be the same as the waveform of the first driving signal V _TX , the amplitude of the second driving signal V _Cancel is the same as the amplitude of the first driving signal V _TX , and the second driving signal V The phase of _Cancel is opposite to that of the first driving signal V _TX .

In step 820, the capacitance C _C of the cancellation capacitor 321 is scanned to obtain a variation curve of the voltage signal V _OUT output by the amplifying circuit 330 with the capacitance C _C of the cancellation capacitor 321, and the capacitance C of the cancellation capacitor 321 is calculated according to the variation curve. _C is configured as the capacitance corresponding to the smallest voltage signal V _OUT .

In step 830, the phase of the second drive signal V _Cancel is scanned to obtain a change curve of the voltage signal V _OUT output by the amplifier circuit 330 with the phase of the second drive signal V _Cancel , and the second drive signal is converted into the second drive signal according to the change curve. The phase of V _Cancel is adjusted to the phase corresponding to the smallest voltage signal V _OUT .

In step 840, the resistance value _RC of the cancellation resistor 323 is scanned to obtain a variation curve of the voltage signal V _OUT output by the amplifying circuit 330 with the resistance value _RC of the cancellation resistor 323, and according to the variation curve, the resistance value of the cancellation resistor 323 is calculated. The resistance value _RC is configured as the resistance value corresponding to the minimum voltage signal V _OUT .

Through the method shown in FIG. 8, the optimal value of the capacitance _C _C of the cancellation capacitor 321, the optimal value of the phase of the second driving signal V _Cancel , and the optimal value of the resistance value RC of the cancellation resistor 323 can be obtained, so that The cancellation efficiency of the cancellation circuit 320 is optimized.

The

above steps

420 and 430 may have other orders, and the

above steps

820, 830 and 840 may also have other orders, which are not limited here.

The parameter adjustment sequence and the adjusted parameters in FIGS. 6 and 7 are only examples. 6 and 7 are described by taking the example that the amplitude of the second driving signal V _Cancel is the same as the amplitude of the first driving signal V _TX . In actual operation, the amplitude of the second driving signal V _Cancel may also be adjusted. At this time, if there is another ratio between the amplitude of the second driving signal V _Cancel and the amplitude of the first driving signal V _TX in

steps

410 and 810 , or if the second driving signal V _Cancel is configured after

steps

410 and 810 The amplitude of , is also adjusted, and accordingly, the capacitance C _C of the offset capacitor 321 also needs to be re-adjusted. For example, at this time, the size of the adjusted capacitor C _C will also change accordingly.

It can be seen that the capacitance detection circuit and the parameter adjustment method of the embodiment of the present application can effectively offset the basic capacitance of the capacitor to be measured, so that the voltage signal output by the amplifying circuit only reflects the capacitance change of the capacitor to be measured, so that the basic capacitance is in the capacitance. The proportion of the dynamic range occupied in the detection circuit is reduced, the amplification factor of the amplifying circuit is increased, the sensitivity of capacitance detection is improved, and the detection performance of the capacitance detection circuit is improved. In addition, in the embodiment of the present application, the influence of parasitic parameters such as screen impedance on capacitance detection in actual situations is considered, and the screen impedance is reduced as much as possible by adjusting the second driving signal, the cancellation capacitor and the cancellation resistance in the capacitance detection circuit. etc. on the capacitance detection.

It can be seen through experiments that by using the capacitance detection circuit and the parameter adjustment method of the embodiment of the present application, the proportion of the dynamic range occupied by the basic capacitance in the capacitance detection circuit can be reduced by more than 80%, and the amplification factor of the amplifying circuit can be increased by one on the original basis. times more.

In the embodiment of the present application, the amplifying circuit includes, for example, a programmable gain amplifier (Programmable Gain Amplifier, PGA), wherein a feedback resistor Rfb is connected between each input end of the PGA and a corresponding output end. Further, a feedback capacitor Cfb is also connected between each input end of the PGA and the corresponding output end.

In addition, the capacitance detection circuit 300 further includes a filter circuit 340 , which is connected to the amplifier circuit 330 and is used for filtering the voltage signal V _OUT output by the amplifier circuit 330 . For example, the anti-aliasing filter (Anti-Alias Filter, AAF) 340 shown in FIG. 9 and FIG. 10 .

Further, the capacitance detection circuit 300 further includes an analog-to-digital conversion circuit 350, the analog-to-digital conversion circuit 350 is connected to the filter circuit 340, and is used for converting the filtered voltage signal V _OUT into a digital signal. For example the ADC 350 shown in FIGS. 9 and 10 .

Further, the capacitance detection circuit 300 further includes a digital processing module 360, the digital processing module 360 is connected with the analog-to-digital conversion circuit 350, and is used for processing the digital signal output by the analog-to-digital conversion circuit 350, so as to obtain the relative value of the capacitor under test 100 relative to the base. The capacitance change ΔC _X of the capacitor C _X . For example, the digital processing module 360 shown in FIGS. 9 and 10 .

An embodiment of the present application further provides a touch control chip, including the capacitance detection circuit 300 in the above-mentioned various embodiments of the present application. The touch control chip is used for determining the touch position of the user on the touch screen according to the capacitance change.

The embodiment of the present application further provides an electronic device, the electronic device includes: a touch screen; and the touch chip in the above embodiment.

As an example and not a limitation, the electronic device in the embodiments of the present application may be a portable or mobile computing device such as a terminal device, a mobile phone, a tablet computer, a notebook computer, a desktop computer, a game device, a vehicle-mounted electronic device, or a wearable smart device, and Electronic databases, automobiles, bank ATMs (Automated Teller Machine, ATM) and other electronic devices. The wearable smart device includes full-featured, large-sized devices that can achieve complete or partial functions without relying on smart phones, such as smart watches or smart glasses; Devices used in conjunction with mobile phones, such as various types of smart bracelets and smart jewelry that monitor physical signs.

It should be noted that, on the premise of no conflict, each embodiment described in this application and/or the technical features in each embodiment can be arbitrarily combined with each other, and the technical solution obtained after the combination should also fall within the protection scope of this application .

It should be understood that the specific examples in the embodiments of the present application are only to help those skilled in the art to better understand the embodiments of the present application, rather than limiting the scope of the embodiments of the present application, and those skilled in the art can Various improvements and modifications can be made, and these improvements or modifications all fall within the protection scope of the present application.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited to this. should be covered within the scope of protection of this application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

A capacitance detection circuit, characterized in that it includes:

a first drive circuit, connected to the capacitor to be tested, for outputting a first drive signal to the capacitor to be tested, wherein the capacitance of the capacitor to be tested is the mutual capacitance between two detection electrodes in the touch screen;

a canceling circuit, including a canceling capacitor and a second driving circuit, the second driving circuit is connected to the canceling capacitor, and is used for outputting a second driving signal to the canceling capacitor; and,

an amplifying circuit, connected to the capacitor to be measured and the cancellation capacitor, and used to output a voltage signal according to the capacitance signal of the capacitor to be measured and the capacitance signal of the cancellation capacitor, wherein the voltage signal is used to determine the The capacitance change of the capacitance of the capacitor to be measured relative to the basic capacitance;

Wherein, the capacitance of the canceling capacitor and the parameters of the second driving signal are configured such that under the condition that the capacitance of the capacitor to be measured does not change relative to the basic capacitance, the output of the amplifying circuit The voltage signal is minimized to cancel the base capacitance of the capacitor under test.
The capacitance detection circuit according to claim 1, wherein the parameter of the second driving signal comprises at least one of the following:

The waveform of the second drive signal, the amplitude of the second drive signal, and the phase of the second drive signal.
The capacitance detection circuit according to claim 2, wherein the waveform of the second driving signal is the same as the waveform of the first driving signal, and the amplitude of the second driving signal is the same as that of the first driving signal. The amplitudes are the same, and the phase difference between the phase of the second driving signal and the phase of the first driving signal is 170° to 190°.
The capacitance detection circuit according to any one of claims 1 to 3, wherein the cancellation circuit further comprises a cancellation resistor connected to the cancellation capacitor.
The capacitance detection circuit according to claim 4, wherein the cancellation resistor is used to cancel the screen impedance of the touch screen.
The capacitance detection circuit according to claim 4, wherein the cancellation resistor is configured such that in the case that the capacitance of the capacitor to be measured does not change relative to the basic capacitance, the output of the amplifying circuit The voltage signal reaches a minimum.
The capacitance detection circuit according to any one of claims 1 to 6, wherein the amplifying circuit comprises a programmable gain amplifier PGA, and feedback is connected between each input end of the PGA and a corresponding output end resistance.
The capacitance detection circuit according to any one of claims 1 to 7, further comprising:

a filtering circuit, connected to the amplifying circuit, for filtering the voltage signal output by the amplifying circuit;

an analog-to-digital conversion circuit, connected to the filter circuit, for converting the filtered voltage signal into a digital signal; and,

A digital processing module, connected to the filter circuit, is used for processing the digital signal to obtain the capacitance variation.
A touch control chip, characterized in that it includes the capacitance detection circuit according to any one of claims 1 to 8, and the touch control chip is used to determine the capacitance change of the capacitor to be measured relative to its basic capacitance to determine The user's touch location on the touch screen.
A method for adjusting parameters of a capacitance detection circuit, characterized in that the capacitance detection circuit includes a first drive circuit, an offset circuit and an amplifying circuit, the first drive circuit is connected to a capacitor to be measured and is used to send the capacitor to the capacitor to be measured. A first drive signal is output, the capacitance of the capacitor to be tested is the mutual capacitance between two detection electrodes in the touch screen, the cancellation circuit includes a cancellation capacitor and a second driving circuit, the second driving circuit and the cancellation a capacitor is connected and used for outputting a second driving signal to the cancellation capacitor, and the amplifying circuit is connected to the capacitor to be tested and the cancellation capacitor and is used for outputting a second drive signal according to the capacitance signal of the capacitor to be tested and the capacitance signal of the cancellation capacitor Outputting a voltage signal, the voltage signal is used to determine the capacitance change of the capacitance of the capacitor to be measured relative to the base capacitance, and the method is used to configure the capacitance of the cancellation capacitor and the parameters of the second driving signal , to offset the basic capacitance of the capacitor under test, wherein the method includes:

Under the condition that the capacitance of the capacitor under test does not change relative to the basic capacitance, the waveform of the second driving signal is configured to be the same as the waveform of the first driving signal, and the amplitude of the second driving signal is the same as that of the first driving signal. The amplitude of the first drive signal is the same, and the phase of the second drive signal is opposite to the phase of the first drive signal;

Scan the capacitance of the cancellation capacitor to obtain a variation curve of the voltage signal output by the amplifying circuit with the capacitance of the cancellation capacitor, and configure the capacitance of the cancellation capacitor to be the smallest according to the variation curve. The capacitance corresponding to the voltage signal;

The phase of the second drive signal is scanned to obtain a change curve of the voltage signal output by the amplifier circuit with the phase of the second drive signal, and the second drive signal is calculated according to the change curve. The phase is adjusted to the phase corresponding to the minimum voltage signal.
The method of claim 10, wherein the method further comprises:

Scan the capacitance of the cancellation capacitor to obtain a variation curve of the voltage signal output by the amplifying circuit with the capacitance of the cancellation capacitor, and adjust the capacitance of the cancellation capacitor to the minimum value according to the variation curve. The capacitance corresponding to the voltage signal.
The method according to claim 10 or 11, wherein the cancellation circuit further comprises a cancellation resistor connected to the cancellation capacitor, and the method further comprises:

Scan the resistance value of the cancellation resistor to obtain a curve of the voltage signal output by the amplifier circuit with the resistance value of the cancellation resistor, and configure the resistance value of the cancellation resistor to the minimum value according to the change curve The resistance value corresponding to the voltage signal, wherein the resistance value of the cancellation resistor before scanning is configured to be 0.
The method according to claim 12, wherein the canceling resistance is used to cancel the screen body impedance of the touch screen.