CN110798195B

CN110798195B - Differential touch detection circuit and touch judgment method using the same

Info

Publication number: CN110798195B
Application number: CN201911152968.5A
Authority: CN
Inventors: 李勇强; 邹晓亮; 吉博
Original assignee: Xi'an Zhongying Electronic Co ltd
Current assignee: Xi'an Zhongying Electronic Co ltd
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2023-06-06
Anticipated expiration: 2039-11-22
Also published as: CN110798195A

Abstract

The invention provides a differential touch detection circuit and a touch judgment method adopting the same. The differential touch detection circuit includes: the circuit comprises a first channel circuit, a second channel circuit, a differential operational amplifier and an analog-to-digital converter, wherein the first channel circuit and the second channel circuit have the same connection structure. The first channel circuit corresponds to a first channel, and the first parasitic capacitance Cx1 is coupled with the first channel circuit through the first touch sensor TK 1; the first channel circuit is coupled to the negative input terminal voltage VIN and the positive output terminal voltage VOP of the differential operational amplifier. The second channel circuit corresponds to a second channel, and a second parasitic capacitance Cx2 is coupled with the second channel circuit through a second touch sensor TK 2; the second channel circuit is coupled to the positive input terminal voltage VIP and the positive output terminal voltage VON of the differential operational amplifier. The two input ends of the analog-to-digital converter are respectively coupled with the VOP and the VON, and the output Vout of the analog-to-digital converter is the difference value between the VOP and the VON.

Description

Differential touch detection circuit and touch judgment method using the same

Technical Field

The invention relates to a touch detection technology.

Background

In a conventional touch system, whether a key is pressed is generally determined according to an output result of a change of a charging time of a parasitic capacitance. Because parasitic capacitance is very easily affected by power supply interference, electromagnetic interference and the like in the whole charging process, the output result is easy to introduce the interference, so that the final judgment result of the key is affected, and false triggering or missing detection of the key is caused.

Therefore, a touch circuit with high anti-interference and a touch determination method are needed.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a differential touch detection circuit and a touch judgment method adopting the differential touch detection circuit.

The differential touch detection circuit provided by the invention comprises:

the circuit comprises a first channel circuit, a second channel circuit, a differential operational amplifier and an analog-to-digital converter, wherein the first channel circuit and the second channel circuit have the same connection structure;

the first channel circuit corresponds to a first channel, and the first parasitic capacitance Cx1 is coupled with the first channel circuit through the first touch sensor TK 1; the first channel circuit is coupled with the negative electrode input end voltage VIN and the positive electrode output end voltage VOP of the differential operational amplifier;

the second channel circuit corresponds to a second channel, and a second parasitic capacitance Cx2 is coupled with the second channel circuit through a second touch sensor TK 2; the second channel circuit is coupled with the voltage VIP at the positive electrode input end and the voltage VON at the positive electrode output end of the differential operational amplifier;

the two input ends of the analog-to-digital converter are respectively coupled with the positive electrode output end voltage VOP and the negative electrode output end voltage VON of the differential operational amplifier, and the output Vout of the analog-to-digital converter is the difference value between the positive electrode output end voltage VOP and the negative electrode output end voltage VON.

In one embodiment, the first channel circuit includes:

a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, a sixth switch S6, a first internal calibration capacitor Cs1, a first internal sensitivity adjustment capacitor Cf1, each having a first end and a second end;

a first end of the first switch S1 is coupled with the working power supply voltage VDD, and a second end of the first switch S1 is coupled with the first touch sensor TK 1;

the first end of the second switch S2 is coupled to the second end of the first switch S1, and the second end of the second switch S2 is coupled to the first end of the sixth switch S6;

a second terminal of the sixth switch S6 is coupled to ground;

the first end of the first internal calibration capacitor Cs1 is coupled to the first end of the sixth switch S6, and the second end of the first internal calibration capacitor Cs1 is coupled to ground;

the first end of the third switch S3 is coupled to the first end of the first internal calibration capacitor Cs1, and the second end of the third switch S3 is coupled to the first end of the fifth switch S5;

a first end of a fifth switch S5 is coupled with the negative electrode input end of the differential operational amplifier, and a second end of the fifth switch S5 is coupled with the positive electrode output end of the differential operational amplifier;

the first internal sensitivity adjustment capacitor Cf1 is connected in parallel with the fifth switch S5.

The first end of the fourth switch S4 is coupled to the positive output end of the differential operational amplifier, and the second end of the fourth switch S4 is coupled to the analog-to-digital converter.

In one embodiment, the second channel circuit includes:

a first switch S1', a second switch S2', a third switch S3', a fourth switch S4', a fifth switch S5', a sixth switch S6', a second internal calibration capacitor Cs2, a second internal sensitivity adjustment capacitor Cf2, each having a first end and a second end;

a first end of the first switch S1 'is coupled with the working power supply voltage VDD, and a second end of the first switch S1' is coupled with the second touch sensor TK 2;

the first end of the second switch S2' is coupled with the second end of the first switch S1, and the second end of the second switch S2' is coupled with the first end of the sixth switch S6';

a second terminal of the sixth switch S6' is coupled to ground;

the first end of the second internal calibration capacitor Cs2 is coupled to the first end of the sixth switch S6', and the second end of the second internal calibration capacitor Cs2 is coupled to ground;

the first end of the third switch S3' is coupled to the first end of the second internal calibration capacitor Cs2, and the second end of the third switch S3' is coupled to the first end of the fifth switch S5 ';

the first end of the fifth switch S5 'is coupled with the positive electrode input end of the differential operational amplifier, and the second end of the fifth switch S5' is coupled with the negative electrode output end of the differential operational amplifier;

the second internal sensitivity adjustment capacitor Cf2 is connected in parallel with the fifth switch S5'.

The first end of the fourth switch S4 'is coupled to the negative output terminal of the differential operational amplifier, and the second end of the fourth switch S4' is coupled to the analog-to-digital converter.

In one embodiment, the first touch sensor TK1 and the second touch sensor TK2 are used to convert touch actions into electrical signals.

In one embodiment, the switches of the differential touch detection circuit are closed and opened during touch key detection in the order of steps in the following table:

step (a)

S1 and S1'

S2 and S2'

S3 and S3'

S4 and S4'

S5 and S5'

S6 and S6'

1

ON

OFF

ON

2

OFF

ON

OFF

ON

OFF

3

OFF

ON

OFF

4

OFF

ON

OFF

Wherein ON represents switch closure, OFF represents switch opening, and S1, S2, S3, S4, S5, S6 represent first switch S1, second switch S2, third switch S3, fourth switch S4, fifth switch S5, sixth switch S6 of the first channel, respectively; s1', S2', S3', S4', S5', S6' represent the first switch S1', the second switch S2', the third switch S3', the fourth switch S4', the fifth switch S5', and the sixth switch S6' of the second channel, respectively.

In one embodiment, when the first internal sensitivity adjustment capacitor Cf1 and the second internal sensitivity adjustment capacitor Cf2 have the same value, the output Vout of the analog-to-digital converter is:

wherein Cx2 is the second parasitic capacitance value, cx1 is the first parasitic capacitance value, cs1 is the first internal calibration capacitance value, cs2 is the second internal calibration capacitance value, and VDD is the operating power supply voltage; cf is the capacitance value of the first internal sensitivity adjustment capacitance Cf1 and the second internal sensitivity adjustment capacitance Cf 2.

In an embodiment, the first internal calibration capacitance Cs1 and the second internal calibration capacitance Cs2 of the differential touch detection circuit are self-calibrated before power-up, and the capacitance values thereof are adjusted to zero the output Vout of the digital-to-analog converter to eliminate the influence of the first parasitic capacitance Cx1 and the second parasitic capacitance Cx2, where cs1=cx1 and cs2=cx2.

In an embodiment, after the self calibration is completed, if a finger presses on a channel, the output Vout of the analog-to-digital converter is:

wherein Cp is the capacitance value of the finger capacitance.

In an embodiment, the differential touch detection circuit further includes a multiplexer, wherein when the number of channels is greater than 2 channels, one of the first channel circuit and the second channel circuit of the differential touch detection circuit is coupled with one of the channels, and the other channel is sequentially connected to the other channel circuit in series through the multiplexer.

The invention also provides a touch judgment method adopting the differential touch detection circuit, which comprises the following steps:

performing self-adaptive calibration before power-on;

starting normal scanning of the touch key;

detecting touch keys of each channel and obtaining a differential data detection result corresponding to each channel; and

and performing key judgment, and judging that the channel is pressed when the difference data detection result is larger than a set threshold value.

In an embodiment, the step of performing adaptive calibration before power-up includes:

before power-up, the capacitance value of the first internal calibration capacitor Cs1 and the capacitance value of the second internal calibration capacitor Cs2 are adjusted to make the output Vout of the digital-to-analog converter zero, so as to eliminate the influence of the first parasitic capacitor Cx1 and the second parasitic capacitor Cx2, and at this time, cx2=cs2 and cx1=cs1.

In an embodiment, the step of performing touch key detection on each channel includes:

the switches of the differential touch detection circuit are closed and opened according to the step sequence in the following table:

step (a)

S1 and S1'

S2 and S2'

S3 and S3'

S4 and S4'

S5 and S5'

S6 and S6'

1

ON

OFF

ON

2

OFF

ON

OFF

ON

OFF

3

OFF

ON

OFF

4

OFF

ON

OFF

Wherein ON represents switch closure, OFF represents switch opening, and S1, S2, S3, S4, S5, S6 represent first switch S1, second switch S2, third switch S3, fourth switch S4, fifth switch S5, sixth switch S6 of the first channel, respectively; s1', S2', S3', S4', S5', S6' represent the first switch S1', the second switch S2', the third switch S3', the fourth switch S4', the fifth switch S5', the sixth switch S6' of the second channel, respectively;

if a finger presses down on a channel, the differential data detection result corresponding to the channel is the output value of the analog-to-digital converter corresponding to the channel

Wherein Cp is the capacitance value of the finger capacitance.

In an embodiment, the method further comprises: when the number of channels is greater than 2, one channel is coupled with one of the first channel circuit and the second channel circuit of the differential touch detection circuit, and the other channel is sequentially connected to the other channel circuit in series through a multiplexer.

The differential touch detection circuit and the method provided by the invention effectively eliminate the influence of parasitic capacitance outside the channel through self calibration, and increase the convenience of PCB layout and wiring. In addition, the differential touch detection circuit and the differential touch detection method make full use of the characteristics of the differential structure, connect the touch channel to two ends of differential input, and judge whether the key is pressed or not by detecting the difference value of the two signals. Because of the symmetry of the difference, when the system-level interference such as power supply or radiation exists outside and the interference caused by environmental change, the two input lines are coupled to the difference at the same time, and the receiving end of the analog-to-digital converter ADC needs to be the difference value of the two signals, so that the common-mode interference of the outside can be completely counteracted, and the anti-interference performance of the system is enhanced. Therefore, the invention has better mass production prospect.

Drawings

The foregoing summary of the invention, as well as the following detailed description of the invention, will be better understood when read in conjunction with the accompanying drawings. It is to be noted that the drawings are merely examples of the claimed invention. In the drawings, like reference numbers indicate identical or similar elements.

FIG. 1 illustrates a differential touch detection circuit according to an embodiment of the invention;

FIG. 2 shows a schematic diagram of the on-off of the touch detection circuit in a first stage of the touch scanning step;

FIG. 3 shows a schematic diagram of the on-off of the touch detection circuit in the second stage during the touch scanning step;

FIG. 4 shows a schematic diagram of the third stage touch detection circuit in the touch scanning step;

FIG. 5 shows a schematic diagram of the on-off of the touch detection circuit in the fourth stage in the touch scanning step;

FIG. 6 shows a schematic diagram of ADC detecting a change in data when a key is pressed;

FIG. 7 shows a schematic diagram of ADC detection data changes when system level disturbances are present;

FIG. 8 is a schematic diagram showing the multi-key scanning timing when there are more than 2 keys; and

fig. 9 illustrates a touch determination method according to an embodiment of the present invention.

Detailed Description

The detailed features and advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description, claims, and drawings that follow.

The following description is merely a specific embodiment of the present application and should not be construed as the only embodiment. It will be apparent to those skilled in the art that various modifications and changes in form and detail may be made without departing from the principles and construction of the invention, but such modifications and changes are still within the scope of the claims of the present application.

In a conventional touch system, whether a key is pressed is generally determined according to an output result of a change of a charging time of a parasitic capacitance. Because parasitic capacitance is very easily affected by power supply interference, electromagnetic interference and the like in the whole charging process, the output result is easy to introduce the interference, so that the final judgment result of the key is affected, and false triggering or missing detection of the key is caused. Therefore, a touch circuit with high anti-interference and a touch determination method are needed.

According to the differential touch detection circuit provided by the invention, the influence of parasitic capacitance outside a channel is effectively eliminated through self calibration, and the convenience of PCB layout and wiring is increased. And fully utilize the characteristic of differential structure, connect the touch channel to the both ends of differential input, judge whether the button presses through detecting the difference of two signals. Because of the symmetry of the difference, when the system-level interference such as power supply or radiation exists outside and the interference caused by environmental change, the two input lines are coupled to the difference at the same time, and the receiving end of the ADC needs to be the difference value of the two signals, so that the common-mode interference of the outside can be completely counteracted, and the anti-interference performance of the system is enhanced. Therefore, the invention has better mass production prospect.

Fig. 1 illustrates a differential touch detection circuit according to an embodiment of the invention. The differential touch detection circuit is used for touch key detection, namely detecting whether a key is actually pressed. Each key may correspond to a channel. Each channel corresponds to a respective PCB parasitic capacitance Cxi, a chip internal calibration capacitance Csi, and an internal sensitivity adjustment capacitance Cfi, where i represents a channel number, for example, cx1 represents a parasitic capacitance corresponding to the first channel (hereinafter referred to as a first parasitic capacitance), cs1 represents a chip internal calibration capacitance corresponding to the first channel (hereinafter referred to as a first internal calibration capacitance), and Cf1 represents an internal sensitivity adjustment capacitance corresponding to the first channel (hereinafter referred to as a first internal sensitivity adjustment capacitance); cx2 denotes a parasitic capacitance corresponding to the second channel (hereinafter referred to as a second parasitic capacitance), cs2 denotes an internal chip calibration capacitance corresponding to the second channel (hereinafter referred to as a second internal calibration capacitance), and Cf2 denotes an internal sensitivity adjustment capacitance corresponding to the second channel (hereinafter referred to as a second internal sensitivity adjustment capacitance); and so on. Although the differential touch detection circuit of fig. 1 shows only two channels, the differential touch detection circuit of the present application is not limited to two-channel application, and can be applied to any number of channels greater than or equal to 2, when there are multiple keys, one of the keys can be used as an input end of the differential operational amplifier OP, and in addition, the key channels can be sequentially connected to another input end of the differential operational amplifier in series through the multiplexer, so as to complete the determination of key touch.

The differential touch detection circuit of the present invention includes a first channel circuit 100, a second channel circuit 200, a differential operational amplifier 102 (OP), and an analog-to-digital converter 103 (ADC). Wherein the first channel circuit 100 and the second channel circuit 200 have the same connection structure.

The first channel circuit 100 corresponds to a first channel. The first parasitic capacitance Cx1 is coupled to the first channel circuit 100 through the first touch sensor TK 1. The first touch sensor TK1 is used to convert a touch action into an electrical signal.

The first channel circuit 100 is coupled to the negative input terminal VIN and the positive output terminal VOP of the differential operational amplifier 102.

The second channel circuit 200 corresponds to a second channel. The second parasitic capacitance Cx2 is coupled to the second channel circuit 200 through the second touch sensor TK 2. The second touch sensor TK2 is used to convert a touch action into an electrical signal.

The second channel circuit 200 is coupled to the positive input terminal VIP and the positive output terminal VON of the differential operational amplifier 102.

The analog-to-digital converter 103 is coupled to the positive output VOP and the negative output VON of the differential operational amplifier 102.

In one embodiment, the first channel circuit 100 includes a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, a sixth switch S6, a first internal calibration capacitor Cs1, and a first internal sensitivity adjustment capacitor Cf1, each having a first end and a second end.

The first terminal of the first switch S1 is coupled to the operating power voltage VDD, and the second terminal of the first switch S1 is coupled to the first touch sensor TK 1.

The first terminal of the second switch S2 is coupled to the second terminal of the first switch S1, and the second terminal of the second switch S2 is coupled to the first terminal of the sixth switch S6.

A second terminal of the sixth switch S6 is coupled to ground.

The first terminal of the first internal calibration capacitor Cs1 is coupled to the first terminal of the sixth switch S6, and the second terminal of the first internal calibration capacitor Cs1 is coupled to ground.

The first terminal of the third switch S3 is coupled to the first terminal of the first internal calibration capacitor Cs1, and the second terminal of the third switch S3 is coupled to the first terminal of the fifth switch S5.

The first end of the fifth switch S5 is coupled to the negative input terminal of the differential operational amplifier 102, and the second end of the fifth switch S5 is coupled to the positive output terminal of the differential operational amplifier 102.

The first end of the fourth switch S4 is coupled to the positive output terminal of the differential operational amplifier 102, and the second end of the fourth switch S4 is coupled to the analog-to-digital converter 103.

In one embodiment, the second channel circuit 200 includes a first switch S1', a second switch S2', a third switch S3', a fourth switch S4', a fifth switch S5', a sixth switch S6', a second internal calibration capacitor Cs2, a second internal sensitivity adjustment capacitor Cf2, each having a first end and a second end.

The first terminal of the first switch S1 'is coupled to the operating power voltage VDD, and the second terminal of the first switch S1' is coupled to the second touch sensor TK 2.

The first terminal of the second switch S2' is coupled to the second terminal of the first switch S1, and the second terminal of the second switch S2' is coupled to the first terminal of the sixth switch S6'.

A second terminal of the sixth switch S6' is coupled to ground.

The first terminal of the second internal calibration capacitor Cs2 is coupled to the first terminal of the sixth switch S6', and the second terminal of the second internal calibration capacitor Cs2 is coupled to ground.

The first terminal of the third switch S3' is coupled to the first terminal of the second internal calibration capacitor Cs2, and the second terminal of the third switch S3' is coupled to the first terminal of the fifth switch S5 '.

The first end of the fifth switch S5 'is coupled to the positive input terminal of the differential operational amplifier 102, and the second end of the fifth switch S5' is coupled to the negative output terminal of the differential operational amplifier 102.

The first terminal of the fourth switch S4 'is coupled to the negative output terminal of the differential operational amplifier 102, and the second terminal of the fourth switch S4' is coupled to the analog-to-digital converter 103.

In one embodiment, the differential touch detection circuit of the present invention further includes a multiplexer, wherein when the number of channels is greater than 2 channels, one channel is coupled to the first channel circuit 100 or the second channel circuit 200 of the differential touch detection circuit, and the other channel is sequentially connected to the other channel circuit in series through the multiplexer.

The touch detection process of the differential touch detection circuit of the present invention may include four steps, wherein, when the formula derives,

representing the common mode voltage of the differential operational amplifier. Table 1 is a truth table for the switching time sequence of the internal switch of the touch channel.

TABLE 1

/>

Step one: S1/S5/S6 is closed, S1'/S5'/S6' is closed, other switches are opened, VDD charges Cx1, cs1 discharges, OP resets, as shown in FIG. 2, at this time, the voltage after charging the two ends of parasitic capacitance Cx1 is V _cx1 The total charge amount is Q1, and Cf1 is not charged; similarly, the charging voltage at both ends of the parasitic capacitance Cx2 is V _cx2 The total charge amount is Q2; at this time, the two ends of Cf2 are not charged;

V _cx1 ＝VDD V _cx2 ＝VDD (1)

Q1＝C _X1 ×V _CX1 ＝C _x1 VDD Q2＝C _X2 ×V _CX2 ＝C _x2 VDD

step two: S2/S5 is closed, S2'/S5' is closed, and the other switches are opened. Cx1 and Cs1 are connected in series, cx1 transfers charge to Cs1, the total charge amount Q1 is unchanged, and the balance voltage of both ends of Cx1 and both ends of Cs1 is V _{CX1_2} The method comprises the steps of carrying out a first treatment on the surface of the Cx2 and Cs2 are connected in series, cx2 transfers charge to Cs2, the total charge quantity Q2 is unchanged, and the balance voltage of both ends of Cx2 and both ends of Cs2 is V _{CX2_2} As shown in fig. 3.

At this time:

Q1＝C _X1 ×V _CX1 ＝(C _X1 +C _S1 )V _{CX1_2}

Q2＝C _X2 ×V _CX2 ＝(C _X2 +C _S2 )V _{CX2_2}

V _{CX1_2} ＝C _X1 V _CX1 /(C _X1 +C _S1 )＝C _X1 VDD/(C _X1 +C _S1 )

and (3) the same principle: v (V) _{CX2_2} ＝C _X2 VDD/(C _X2 +C _S2 ) (2)

Step three: S2/S3 is closed, S2'/S3' is closed, other switches are opened, the capacitance Cf1=Cf2 of the sensitivity adjustment capacitor is set, cx1 and Cs1 continue to discharge to Vocm, and Cf1 is charged at the moment; cx2 and Cs2 continue to discharge to Vocm, at which point Cf2 charges, as shown in fig. 4.

At this time: the voltage across Vcx1 decreases to V _{CX1_3} The magnitude of which is Vocm, the redundant charge is stored in the upper part Cf1 of the differential amplifier, the charge quantity of which is Qf1, and the voltage across Vcx2 is reduced to V _{CX2_3} The excess charge is stored in Cf2 of the lower part of the differential amplifier, having a magnitude of Vocm, the charge quantity being Qf2, i.e

V _{CX1_3} ＝V _OCM

V _{CX2_3} ＝V _OCM

The upper portion Cf1 stores an amount of charge Qf1, the lower portion Cf2 stores an amount of charge Qf2, and q1= (Q _CX1 +Q _CS1 )+Q _f1 Q2＝(Q _CX2 +Q _CS2 )+Q _f2 I.e.

C _X1 VDD＝(C _X1 +C _S1 )V _{CX1_3} +Q _f1

Q _f1 ＝C _X1 VDD-(C _X1 +C _S1 )V _OCM

C _X2 VDD＝(C _X2 +C _S2 )V _{CX2_3} +Q _f2

Q _f2 ＝C _X2 VDD-(C _X2 +C _S2 )V _OCM

The voltages at the positive and negative output terminals of the differential amplifier 102 (OP) are respectively:

step four: S4/S4' is closed, other switches are opened, the capacitance Cf1=Cf2=Cf of the sensitivity adjustment capacitor is set, the differential ADC collects Vout voltage, namely, the ADC collection and conversion are started on the basis of the third step, and all voltages are not changed; as shown in fig. 5.

At this time: the differential ADC initiates conversion of the difference between VOP and VON, i.e

The differential touch detection circuit of the present invention operates as a whole as follows.

1. After power-on, the system performs self-calibration according to the PCB, namely, according to algorithm polling, the size of Csi corresponding to each channel is adjusted to match with external Cxi, so that the final differential ADC sampling value Vout is 0; thus, cxi=csi is realized, and the influence caused by external parasitic capacitance is eliminated;

2. because the system eliminates the influence of external parasitic capacitance, the TK wiring of the PCB differential two-path touch sensor is not required to be completely symmetrical;

3. after the system self-calibration, writing the corresponding calibration capacitance value Csi and other corresponding parameters (such as channel enabling, switching frequency and Cf size) into an internal RAM; if it is assumed at this time that the second channel (TK 2) has been pressed by a finger, cx2 parasitic capacitance increases to C' _X2 ＝C _X2 +C _p (Cp is finger capacitance), cs1 = cx1, cs2 = cx2, then according to the differential principle described above

As can be seen from equation (5) above, after self-calibration, the sampled data value (i.e., vout) for each channel is no longer affected by parasitic capacitance, but is related to Cp, VDD, and Cf only. The current touch variation Vout can be calculated by sampling with an analog-to-digital converter 103 (ADC), and writing the value into the RAM of the corresponding channel, as shown in fig. 6.

4. When the external power supply noise or radiation interference exists, the two channels are almost simultaneously coupled, and for the differential ADC, the difference value of the two signals is sampled, so that the external common mode interference can be completely counteracted, and the anti-interference performance of the system is enhanced, as shown in fig. 7.

5. In the case of two keys, if there are multiple keys, one of the keys may be used as one end of the differential input, and the key channels are sequentially connected to the other end of the differential, so as to complete the determination of the keys, as shown in fig. 8.

Fig. 9 shows a touch determination flow according to an embodiment of the present invention.

Step 901: and (5) powering up the self-adaptive calibration. The external parasitic capacitance Cxi is matched by adjusting the size of Csi corresponding to each channel, so as to eliminate the influence of the parasitic capacitance.

In one embodiment, polling may be performed according to an algorithm, by adjusting the size of Csi corresponding to each channel, and matching the outer Cxi, so that the final ADC sampling result Vout is 0 (because the finger capacitance is 0 before touching), so that cxi=csi is eliminated, and the influence caused by the outer parasitic capacitance is eliminated. At this time, the corresponding calibration capacitance Csi and other corresponding parameters (e.g. channel enable, switching frequency, cf size) are also written into the internal RAM (not shown).

Step 902: and starting normal scanning of the touch key.

Step 903: and detecting TKi differential data, namely performing touch key scanning process on each touch channel. This step may include the processes of steps one through four described above.

Step 904: and extracting a differential data result. And extracting the analog-digital conversion result Vout value from the RAM corresponding to each channel.

Step 905: and (5) data processing. The extracted data (i.e., vout values corresponding to the channels) are subjected to algorithmic processing such as filtering.

Step 906: and (5) key judgment. The processed Vout value is compared with a set threshold Vth, and when Vout > Vth, it is determined that a key is pressed.

performing self-adaptive calibration before power-on;

starting normal scanning of the touch key;

step (a)

S1 and S1'

S2 and S2'

S3 and S3'

S4 and S4'

S5 and S5'

S6 and S6'

1

ON

OFF

ON

2

OFF

ON

OFF

ON

OFF

3

OFF

ON

OFF

4

OFF

ON

OFF

Wherein Cp is the capacitance value of the finger capacitance.

As used in this application and in the claims, the terms "a," "an," "the," and/or "the" are not specific to the singular, but may include the plural, unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that the steps and elements are explicitly identified, and they do not constitute an exclusive list, as other steps or elements may be included in a method or apparatus.

This application uses specific words to describe embodiments of the application. Reference to "one embodiment," "an embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic is associated with at least one embodiment of the present application. Thus, it should be emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various positions in this specification are not necessarily referring to the same embodiment. Furthermore, certain features, structures, or characteristics of one or more embodiments of the present application may be combined as suitable.

Likewise, it should be noted that in order to simplify the presentation disclosed herein and thereby aid in understanding one or more inventive embodiments, various features are sometimes grouped together in a single embodiment, figure, or description thereof. This method of disclosure, however, is not intended to imply that more features than are presented in the claims are required for the subject application.

Furthermore, the order in which the elements and sequences are presented, the use of numerical letters, or other designations are used in the application and are not intended to limit the order in which the processes and methods of the application are performed unless explicitly recited in the claims. While certain presently useful inventive embodiments have been discussed in the foregoing disclosure, by way of various examples, it is to be understood that such details are merely illustrative and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover all modifications and equivalent arrangements included within the spirit and scope of the embodiments of the present application. For example, although the apparatus or system described above may be implemented by a hardware device, there are also possibilities that are implemented by a software solution.

Those skilled in the art will appreciate that various modifications and improvements to the disclosure herein may occur. For example, the different system components described above are all implemented by hardware devices, but may also be implemented by software-only solutions. Furthermore, the provision of location information as disclosed herein may be implemented by a firmware, a combination of firmware/software, a combination of firmware/hardware or a combination of hardware/firmware/software.

The terms and expressions which have been employed herein are used as terms of description and not of limitation. The use of these terms and expressions is not meant to exclude any equivalents of the features shown and described (or portions thereof), and it is recognized that various modifications are possible and are intended to be included within the scope of the claims. Other modifications, variations, and alternatives are also possible. Accordingly, the claims should be looked to in order to cover all such equivalents.

Also, it should be noted that while the present invention has been described with reference to the particular embodiments presently, it will be appreciated by those skilled in the art that the above embodiments are provided for illustration only and that various equivalent changes or substitutions may be made without departing from the spirit of the invention, and therefore, the changes and modifications to the above embodiments shall fall within the scope of the claims of the present application as long as they are within the true spirit of the invention.

Claims

1. A differential touch detection circuit, the differential touch detection circuit comprising:

the two input ends of the analog-to-digital converter are respectively coupled with the positive electrode output end voltage VOP and the negative electrode output end voltage VON of the differential operational amplifier, and the output Vout of the analog-to-digital converter is the difference value between the positive electrode output end voltage VOP and the negative electrode output end voltage VON;

the first channel circuit comprises a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, a sixth switch S6, a first internal calibration capacitor Cs1, and a first internal sensitivity adjustment capacitor Cf1, each having a first end and a second end;

a second terminal of the sixth switch S6 is coupled to ground;

the first internal sensitivity adjustment capacitor Cf1 is connected in parallel with the fifth switch S5;

the first end of the fourth switch S4 is coupled with the positive electrode output end of the differential operational amplifier, and the second end of the fourth switch S4 is coupled with the analog-to-digital converter;

wherein the second channel circuit comprises a first switch S1', a second switch S2', a third switch S3', a fourth switch S4', a fifth switch S5', a sixth switch S6', a second internal calibration capacitor Cs2, a second internal sensitivity adjustment capacitor Cf2, each having a first end and a second end;

a second terminal of the sixth switch S6' is coupled to ground;

the first end of the second internal calibration capacitor Cs2 is coupled to the first end of the sixth switch S6', and the second end of the second internal calibration capacitor Cs2 is coupled to ground; the first channel circuit comprises

the second internal sensitivity adjustment capacitor Cf2 is connected in parallel with the fifth switch S5';

2. The differential touch detection circuit of claim 1, wherein the first touch sensor TK1 and the second touch sensor TK2 are configured to convert touch actions into electrical signals.

3. The differential touch detection circuit of claim 1, wherein the switches of the differential touch detection circuit are closed and opened during touch key detection in the order of steps in the following table:

step (a) S1 and S1' S2 and S2' S3 and S3' S4 and S4' S5 and S5' S6 and S6' 1 ON OFF OFF OFF ON ON 2 OFF ON OFF OFF ON OFF 3 OFF ON ON OFF OFF OFF 4 OFF OFF OFF ON OFF OFF

4. The differential touch detection circuit of claim 3 wherein, in the case where the first internal sensitivity adjustment capacitance Cf1 and the second internal sensitivity adjustment capacitance Cf2 are equal in value, the output Vout of the analog-to-digital converter is:

5. The differential touch detection circuit of claim 4, wherein the first internal calibration capacitance Cs1 and the second internal calibration capacitance Cs2 of the differential touch detection circuit are self-calibrated prior to power-up, the capacitance values of which are adjusted to zero the output Vout of the analog-to-digital converter to eliminate the effects of the first parasitic capacitance Cx1 and the second parasitic capacitance Cx2, at which time cx2=cs2, cx1=cs1.

6. The differential touch detection circuit of claim 5, wherein after self calibration, the output Vout of the analog-to-digital converter is:

wherein Cp is the capacitance value of the finger capacitance.

7. The differential touch detection circuit of claim 5, further comprising a multiplexer, wherein when the number of channels is greater than 2 channels, one of the first channel circuit and the second channel circuit of the differential touch detection circuit is coupled with one of the channels, and the other channel is serially connected to the other channel circuit in sequence through the multiplexer.

8. A touch judgment method employing the differential touch detection circuit according to claim 1, the method comprising:

performing self-adaptive calibration before power-on;

starting normal scanning of the touch key;

9. The method of claim 8, wherein the step of adaptively calibrating prior to power-up comprises:

before power-up, the capacitance value of the first internal calibration capacitor Cs1 and the capacitance value of the second internal calibration capacitor Cs2 are adjusted to make the output Vout of the analog-to-digital converter zero, so as to eliminate the influence of the first parasitic capacitor Cx1 and the second parasitic capacitor Cx2, and at this time, cx2=cs2 and cx1=cs1.

10. The method of claim 8, wherein the step of touch key detection for each channel comprises:

Wherein Cp is the capacitance value of the finger capacitance.

11. The method of claim 8, wherein the method further comprises:

when the number of channels is greater than 2, one channel is coupled with one of the first channel circuit and the second channel circuit of the differential touch detection circuit, and the other channel is sequentially connected to the other channel circuit in series through a multiplexer.