CN104199581B - A capacitance detection circuit and capacitance detection device based on large CTP and small CTP - Google Patents

Abstract

The present invention relates to electronic applications, disclose a kind of based on big C_TP, little C_TPCapacitive detection circuit and capacitance detecting device.In the present invention, comprising：Electric capacity C on screen_TP, feedback capacity C_fWith an operational amplifier；Also include：Programmable capacitor array Cs, the first charge switch, the second charge switch, the first change-over switch and the second change-over switch；C_TPOne end be connected with the first bias voltage by the first charge switch, and be connected with the negative input end of operational amplifier by the first change-over switch, C_TPThe other end ground connection；One end of Cs is connected with the second bias voltage by the second charge switch, and is connected with the negative input end of operational amplifier by the second change-over switch, the other end ground connection of Cs；Wherein, the first bias voltage is less than the second bias voltage.The output common mode level of amplifier is adjusted by the Cs for increasing newly, expands the output common mode level amplitude of oscillation, improve capacitance detecting sensitivity.

Description

A capacitance detection circuit and capacitance detection device based on large CTP and small CTP

technical field

The invention relates to the field of electronics, in particular to a capacitance detection circuit based on a large _CTP , a capacitance detection circuit and a capacitance detection device based on a small _CTP .

Background technique

In recent years, capacitive touch screens have been widely used in the design of smart terminals due to their advantages of simple and convenient operation, high light transmittance, and wear resistance, such as single-point touch and multi-point touch. The capacitive touch screen mainly detects whether there is a touch by detecting the change of capacitance on the screen. With the development of capacitive technology, higher requirements are put forward for its sensitivity and precision. How to accurately judge the position of the slight touch point has become a problem that needs to be solved at present.

In the prior art, as shown in FIG. 1 , the detection circuit mainly includes an on-screen capacitor C _TP , a feedback capacitor C _f and an operational amplifier 101. The capacitance detection process is mainly divided into two modes: charging and switching. Using the charging switch 104, The transfer switch 105 and the charging switch 106 are controlled. Specifically, in the charging mode, the charging switch 104 and the charging switch 106 are closed, and the transfer switch 105 is opened, and the circuit connection thereof is shown in FIG. 2 . In this mode, the built-in bias voltage V _TP charges the on-screen capacitor C _TP , The feedback capacitor C _f is in the reset state; and in the conversion mode, the charging switch 104 and the charging switch 106 are opened, and the conversion switch 105 is closed.

At this time, if the capacitance on the screen changes △C _TP , the output of the op amp changes as follows:

Since in actual design and application, considering the finished product of the chip, C _TP will be much larger than C _f , so The value is larger, and because the maximum variation range of V _OUT is (0, V _DD ), according to the above formula (1), it can be obtained that in order to ensure that V _OUT does not exceed the output range of the op amp, (V _TP -V _CM ) needs It can be obtained according to △Q=(V _CM -V _TP )△C _TP , the variation range of △Q will become very small due to the limitation of (V _TP -V _CM ), so that the input during touch detection The signal-to-noise ratio is reduced, and the anti-interference ability is reduced, resulting in limited sensitivity of capacitance detection.

Contents of the invention

The object of the present invention is to provide a capacitance detection circuit and capacitance detection device based on large C _TP and small C _TP , so that the capacitance detection circuit can expand the output common-mode level swing and improve the sensitivity of capacitance detection.

In order to solve the above technical problems, the embodiment of the present invention provides a capacitance detection circuit based on large C _TP , comprising: on-screen capacitance C _TP , feedback capacitance Cf and an operational amplifier; the capacitance detection circuit based on large C _TP It also includes: a programmable capacitor array Cs, a first charging switch, a second charging switch, a first transfer switch, and a second transfer switch;

One end of the C _TP is connected to the first bias voltage through the first charging switch, and is connected to the negative input end of the operational amplifier through the first transfer switch, and the other end of the C _TP is grounded;

One end of the Cs is connected to the second bias voltage through the second charging switch, and is connected to the negative input end of the operational amplifier through the second transfer switch, and the other end of the Cs is grounded;

Wherein, the first bias voltage is smaller than the second bias voltage.

Embodiments of the present invention also provide a capacitance detection circuit based on a small C _TP , including: an on-screen capacitance C _TP , a feedback capacitance Cf, and an operational amplifier; the capacitance detection circuit based on a small C _TP also includes: a programmable a capacitor array Cs, a first charging switch, a second charging switch, a first transfer switch and a second transfer switch;

One end of the C _TP is connected to the second bias voltage through the first charging switch, and is connected to the negative input end of the operational amplifier through the first transfer switch, and the other end of the C _TP is grounded;

One end of the Cs is connected to the first bias voltage through the second charging switch, and is connected to the negative input end of the operational amplifier through the second transfer switch, and the other end of the Cs is grounded;

Wherein, the first bias voltage is smaller than the second bias voltage.

Embodiments of the present invention also provide a capacitance detection device, including: the capacitance detection circuit based on the large C _TP as described above and the capacitance detection circuit based on the small C _TP as described above, and also includes a selector;

When the value of the capacitance C _TP on the screen is greater than the value of the programmable capacitance array Cs, the selector is connected to the capacitance detection circuit based on the large C _TP ;

When the value of the on-screen capacitance C _TP is smaller than the value of the programmable capacitance array Cs, the selector connects to the small C _TP based capacitance detection circuit.

Compared with the prior art, the embodiment of the present invention adds a programmable capacitor array Cs, and uses different bias voltages to charge C _TP and Cs respectively during the charging phase of capacitance detection, and can use Cs absorbs part of the charge of the capacitor C _TP on the screen to adjust the output common mode level of the operational amplifier, expand the output common mode level swing, and improve the sensitivity of capacitance detection.

As a further improvement, the capacitance detection circuit based on the large C _TP also includes: a third charging switch, a fourth charging switch, and a third transfer switch; one end of the Cf is grounded through the third charging switch, and is grounded through the third charging switch. The third transfer switch is connected to the negative input terminal of the operational amplifier, and the other end of the Cf is connected to the negative input terminal of the operational amplifier through the fourth charging switch.

Use the charging switch and the transfer switch to adjust the connection of Cf, so that in the charging stage, the output voltage of the operational amplifier is used to charge Cf, and Cf is reversely precharged with a certain amount of electricity, which can further expand the range of output common-mode level changes.

As a further improvement, the capacitance detection circuit based on a large C _TP also includes: a fifth charging switch, a sixth charging switch, a seventh charging switch, a fourth transfer switch, and a fifth transfer switch; one end of the Cf passes through the The fifth charging switch is grounded, and connected to the negative input terminal of the operational amplifier through the fourth transfer switch; the other end of the Cf is connected to the third bias voltage Vs through the sixth charging switch, and connected to the third bias voltage Vs through the The fifth transfer switch is connected to the output terminal of the operational amplifier; the negative input terminal of the operational amplifier is connected to the output terminal through the seventh charging switch.

Use the charging switch and the transfer switch to adjust the connection of Cf, so that in the charging stage, a controllable bias voltage Vs is used to charge Cf, and Cf is reversely precharged with a certain amount of electricity, which further expands the variation range of the output common mode level. At the same time, the range of variation is more controllable.

Description of drawings

Fig. 1 is according to the capacitance detection circuit structural diagram in the background technology;

Fig. 2 is a charging state structure diagram according to the capacitance detection circuit in the background technology;

Fig. 3 is a switching state structure diagram according to the capacitance detection circuit in the background technology;

Fig. 4 is a structure diagram of a capacitance detection circuit based on a large C _TP in the first embodiment;

Fig. 5 is according to the charging state structural diagram of the capacitance detection circuit based on large C _TP in the first embodiment;

FIG. 6 is a structural diagram of the conversion state of the capacitance detection circuit based on a large C _TP in the first embodiment;

FIG. 7 is a structural diagram of a capacitance detection circuit based on a large C _TP in the second embodiment;

Fig. 8 is a structure diagram of a capacitance detection circuit based on a large C _TP according to a third embodiment;

FIG. 9 is a structural diagram of a capacitance detection circuit based on a small _CTP in the fourth embodiment;

Fig. 10 is a structure diagram of a capacitance detection circuit based on a small _CTP according to the fifth embodiment;

FIG. 11 is a structural diagram of a capacitance detection circuit based on a small _CTP according to the sixth embodiment;

Fig. 12 is a structural block diagram of a capacitance detection device according to a seventh embodiment;

FIG. 13 is a circuit configuration diagram of a capacitance detection device according to a seventh embodiment.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, various embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that, in each implementation manner of the present invention, many technical details are provided for readers to better understand the present application. However, even without these technical details and various changes and modifications based on the following implementation modes, the technical solution claimed in each claim of the present application can be realized.

The inventors of the present invention found that in the application of the existing capacitance detection circuit, the capacitance C _TP corresponding to different touch screens varies greatly, in order to make the present invention have a wider application range. The adjustment of the charging level of C _TP can be fully utilized, so that the detected capacitance range is the largest. In addition, when the on-screen capacitance is large or small, the variation range of the output common-mode level may be different. If a capacitance detection circuit is designed for different on-screen capacitance values, the output dynamic range of the operational amplifier can be fully amplified. Testers can know from experience whether the on-screen capacitance value of the applied capacitive screen is large or small, so designing different capacitance detection circuits according to different on-screen capacitance values can effectively expand the variation range of the output common-mode level .

The first embodiment of the present invention relates to a capacitance detection circuit based on a large C _TP , the circuit structure of which is shown in _FIG . , a programmable capacitor array Cs, a first charging switch 201 , a second charging switch 203 , a charging switch 205 , a first transfer switch 202 and a second transfer switch 204 .

The capacitance detection circuit based on the large C _TP in this embodiment is specifically connected as follows: the resistor 102 is connected between the positive input terminal of the operational amplifier 101 and the bias voltage _VCM , and the capacitor 103 is connected between the positive input terminal of the operational amplifier 101 and the ground terminal. Cf is connected between the negative input terminal and the output terminal of the operational amplifier 101, and the charging switch 205 is connected in parallel at both ends of Cf; one end of C _TP is connected with the first bias voltage V1 through the first charging switch 201, and through The first transfer switch 202 is connected to the negative input terminal of the operational amplifier 101, and the other end of _CTP is grounded; one end of Cs is connected to the second bias voltage V2 through the second charging switch 203, and is connected to the operational amplifier through the second transfer switch 204. The negative input terminal of 101 is connected, and the other end of Cs is grounded. It should be noted that the first bias voltage V1 in this embodiment is smaller than the second bias voltage V2.

In practical applications, in the charging stage, the first charging switch 201, the second charging switch 203 and the charging switch 205 are respectively closed, the first transfer switch 202 and the second transfer switch 204 are opened, and the circuit structure changes as shown in FIG. 5 ; At this time, C _TP is connected between the first bias voltage V1 and the ground terminal, and the two ends of Cf are short-circuited, the first bias voltage V1 charges C _TP , the second bias voltage V2 charges Cs, and at the same time Cf clears zero. In the conversion stage, the first charging switch 201, the second charging switch 203 and the charging switch 205 are respectively opened, the first transfer switch 202 and the second transfer switch 204 are closed, and the circuit structure changes as shown in Figure 6; C _TP is connected to Between the negative input terminal of the operational amplifier 101 and the ground terminal, Cs is connected between the negative input terminal of the operational amplifier 101 and the ground terminal, Cf is directly connected between the negative input terminal and the output terminal of the operational amplifier 101, and the charge of C _TP passed to Cf and Cs, respectively.

Specifically, in the conversion stage of the capacitance detection circuit based on the large C _TP in this embodiment, according to the charge conservation and the imaginary short characteristic of the operational amplifier, the final operational amplifier output can be obtained as follows (3):

If the capacitance on the screen changes as C _TP +△C _TP , the output of the op amp changes as the following equation (4)

It can be seen from the above formula (3) that a part of the charge of the capacitor C _TP on the screen will be absorbed by the capacitor array C _s , so the output common mode level of the op amp can be easily adjusted, that is, by adjusting the size of C _s To offset the limitation of the circuit's DC working state on the output common-mode level. Therefore, when the circuit is performing detection work, it is necessary to perform an initial "frequency modulation" process on the programmable capacitor array C _s , the purpose of which is to make the output of the operational amplifier be the common-mode level V _CM , that is, to make the formula (3) V _OUT in =V _CM . At this point, the above formula (4) can be changed into the following formula (5):

Among them, (V _CM -V ₁ ) can be increased without restriction, that is to say, the change of the output common-mode level will not be limited by the DC working state of the circuit and will be enlarged, which improves the sensitivity of the capacitance detection circuit.

In addition, since V _OUT =V _CM , the following equation (6) can be obtained:

In this embodiment, generally large C _TP is understood as its capacitance value satisfies C _TP >C _s , and its dynamic output range is from V _CM to V _DD , that is, the DC of the operational amplifier can be adjusted by reducing the common-mode level V _CM Operating Voltage.

For example, assuming that C _TP =80 _p F at this time (the capacitance value is relatively large), at the same time, you can set V ₁ =0, V ₂ =V _DD , V _CM =V _DD /3, and C _s =40 _p F to Make the operational amplifier output V _OUT =V _CM . Afterwards, when there is a finger touch, the capacitance on the screen increases △C _TP , and the output of the operational amplifier increases Since the common-mode level V _CM =V _DD /3 at this time, the dynamic detection range of its output is from V _DD /3 to V _DD , with a maximum variation of 2*V _DD /3, so it can be adjusted by adjusting C _f to enhance the sensitivity of detection, according to the above formula (5), it can be seen that its size is:

Among them, △C _TP,max is the maximum variation range of capacitance on the screen.

The final capacitance-to-voltage conversion gain can be obtained as

Compared with the prior art, this embodiment adds a programmable capacitor array Cs. In the charging stage of capacitance detection, different bias voltages are used to charge _CTP and Cs respectively. In the conversion stage of capacitance detection, Cs can be used Absorb part of the charge of the capacitor C _TP on the screen, so as to eliminate the influence of the DC working state of the circuit on the output dynamic range of the capacitance detection circuit, adjust the output common mode level of the operational amplifier, expand the output common mode level swing, and improve the detection sensitivity .

The second embodiment of the present invention relates to a large C _TP based capacitance detection circuit. The second embodiment is further improved on the basis of the first embodiment, and the main improvement is that: in the charging phase of the first embodiment, both ends of Cf are short-circuited so that Cf is cleared to zero. In the second embodiment of the present invention, the connection of Cf is adjusted by the charging switch and the transfer switch, so that in the charging stage, the output voltage of the operational amplifier is used to charge Cf, and Cf is reversely precharged with a certain amount of electricity, which can further expand the output common. Modulo level variation range.

Specifically, the large C _TP -based capacitance detection circuit in this embodiment is shown in Figure 7, and also includes: a third charging switch 206, a fourth charging switch 208, and a third transfer switch 207; one end of Cf passes through the third The charging switch 206 is grounded and connected to the negative input terminal of the operational amplifier 101 through the third transfer switch 207 , and the other end of Cf is connected to the negative input terminal of the operational amplifier 101 through the fourth charging switch 208 .

Since Cf is connected between the output terminal of the operational amplifier and the ground terminal during the charging phase, that is, during the charging phase, Cf is precharged with a reverse charge, which can also be obtained according to the conservation of charge and the imaginary short characteristic of the operational amplifier, V The lower limit of variation of _OUT will be lower, and its variation range will be larger, and the sensitivity of the capacitance detection circuit based on a large C _TP in this embodiment will be higher.

The third embodiment of the present invention also relates to a large C _TP based capacitance detection circuit. The third embodiment is further improved on the basis of the first embodiment, and the main improvements are as follows: In the first embodiment, both ends of Cf are short-circuited during the charging phase, so that Cf is cleared to zero. In the third embodiment of the present invention, the controllable bias voltage Vs is used to charge Cf, and Cf is reversely precharged with a certain amount of electricity. While further expanding the variation range of the output common-mode level, the variation range is more extensive. controllable.

The inventors of the present invention found that in the second embodiment, although the output of the op amp has been adjusted to (V _CM ~ V _DD ), there is still a certain margin in its swing, which can be achieved by making full use of the charge precharged by C _f amount, so as to further increase the output swing.

Specifically, the capacitance detection circuit based on the large C _TP in this embodiment is shown in FIG. The fifth transfer switch 211 . Wherein, one end of Cf is grounded through the fifth charging switch 212, and is connected to the negative input end of the operational amplifier 101 through the fourth transfer switch 209; the other end of Cf is connected to the third bias voltage Vs through the sixth charging switch 210, and is connected through The fifth transfer switch 211 is connected to the output terminal of the operational amplifier 101 ; the negative input terminal of the operational amplifier 101 is connected to the output terminal through the seventh charging switch 213 .

Similar to the second embodiment, since Cf is connected between the output terminal of the operational amplifier and the ground terminal during the charging phase, that is, during the charging phase, Cf is precharged with reverse charges, also according to the conservation of charge and the operational amplifier The imaginary short characteristic can change the above formula (3) into:

It can be seen that the output of the operational amplifier becomes (V _CM -V _S ～V _DD ), the lower limit of V _OUT will be lower, the range of variation will be larger, and the sensitivity will be further improved.

For example, if V _CM =V _S =V _DD /2 is set at this time, the swing of the operational amplifier can reach ( _{0˜V DD} ).

The fourth embodiment of the present invention relates to a capacitance detection circuit based on a small C _TP , and its circuit structure is shown in _FIG . , a programmable capacitor array Cs, a first charging switch 201 , a second charging switch 203 , a charging switch 205 , a first transfer switch 202 and a second transfer switch 204 .

Because the capacitance detection circuit in this embodiment is based on a small C _TP capacitance detection circuit, its connection structure is compared with the first embodiment, the only difference is that the second bias voltage V2 is used to charge C _TP during the charging phase, and the first The bias voltage V1 charges Cs. Under the premise of small C _TP detection, in order to ensure the normal operation of the op amp, the bias voltage for charging C _TP needs to be greater than the bias voltage for charging Cs. Other connection structures and design principles are similar to those of the first embodiment, and will not be repeated here.

The fifth embodiment of the present invention relates to a small C _TP based capacitance detection circuit. The fifth embodiment is further improved on the basis of the fourth embodiment, and the main improvement is that: in the fourth embodiment, both ends of Cf are short-circuited during the charging phase, so that Cf is cleared to zero. In the fifth embodiment of the present invention, the connection of Cf is adjusted by the charging switch and the changeover switch, so that in the charging stage, the output voltage of the operational amplifier is used to charge Cf, and Cf is reversely precharged with a certain amount of electricity, which can further expand the output common. Modulo level variation range.

Specifically, the circuit of the small _CTP -based capacitance detection circuit in this embodiment is shown in FIG. 10 , and its connection structure is roughly the same as that in FIG. 7 in the second embodiment. The capacitance detection circuit of small C _TP also comprises: the 3rd charge switch 206, the 4th charge switch 208 and the 3rd changeover switch 207; One end of Cf is grounded by the 3rd charge switch, and through the negative input of the 3rd changeover switch and operational amplifier The other end of Cf is connected with the negative input end of the operational amplifier through the fourth charging switch. In the charging phase, the bias voltage for charging C _TP is greater than that for Cs. That is to say, in the charging stage, the output voltage of the operational amplifier is used to charge Cf, and Cf is reversely precharged with a certain amount of electricity; The virtual short characteristic of the final op amp output can be obtained as:

At this time, if the capacitance on the screen changes as C _TP +△C _TP , the output of the op amp changes as:

At this time, in order to adjust the output common mode level of the op amp, it is necessary to make C _s satisfy:

For example, assuming that the capacitance to be detected is C _TP =20 _p F, you can set V ₁ =0, V ₂ =V _DD , V _CM =V _DD /3, C _s =40 _p F to make the operation amplifier output V _OUT =2*V _CM . It can be seen from formula (8) that if the capacitance on the screen increases △C _TP at this time, the output of the op amp will decrease Since the output DC level of the operational amplifier at this time is 2*V _DD /3, its output still has a dynamic detection range of 2*V _DD /3, and the size of the feedback capacitor C _f at this time can be set as:

Among them, △C _TP,max is the maximum change range of capacitance on the screen at this time.

If V _CM =V _DD /2, then the output swing of the operational amplifier can reach the maximum range from V _DD to 0.

The sixth embodiment of the present invention also relates to a small C _TP based capacitance detection circuit. The sixth embodiment is further improved on the basis of the fourth embodiment, and the main improvement is that: in the charging phase of the fourth embodiment, both ends of Cf are short-circuited so that Cf is cleared to zero. In the charging stage in the sixth embodiment of the present invention, the controllable bias voltage Vs is used to charge Cf, and Cf is reversely precharged with a certain amount of electricity, while further expanding the variation range of the output common-mode level, so that The range of variation is more controllable.

Specifically, the small C _TP -based capacitance detection circuit in this embodiment is shown in Figure 11, and its connection structure is roughly the same as that in Figure 8 in the third embodiment, the main difference is that the small C TP-based capacitance detection circuit in this embodiment is The capacitance detection circuit of _TP also includes: a fifth charging switch 212 , a sixth charging switch 210 , a seventh charging switch 213 , a fourth transfer switch 209 and a fifth transfer switch 211 . Wherein, one end of Cf is grounded through the fifth charging switch 212, and is connected to the negative input end of the operational amplifier 101 through the fourth transfer switch 209; the other end of Cf is connected to the third bias voltage Vs through the sixth charging switch 210, and is connected through The fifth transfer switch 211 is connected to the output terminal of the operational amplifier 101 ; the negative input terminal of the operational amplifier 101 is connected to the output terminal through the seventh charging switch 213 . In the charging phase, the bias voltage for charging C _TP is greater than that for Cs.

That is to say, in the charging phase, a controllable third bias voltage Vs is used to charge Cf; in the conversion phase, its connection is the same as that of Figure 6 in the first embodiment, according to the conservation of charge and the virtual short characteristic of the operational amplifier It can be obtained that the lower limit of variation of V _OUT will be controllable while being lower, its variation range will be larger, and the sensitivity will be further improved.

A seventh embodiment of the present invention relates to a capacitance detection device. Its structural block diagram is shown in Figure 12, which specifically includes: a capacitance detection circuit based on a large C _TP as in any one of the first to third embodiments and a small C TP-based capacitance detection circuit as in any of the fourth to sixth embodiments. The capacitance detection circuit of _TP also includes a selector. Use the selector to integrate the capacitance detection circuit based on large C _TP and the capacitance detection circuit based on small C _TP , so that when the capacitance detection chip is produced, the components in it can be reused in large quantities. At the same time, according to different C _TP values, Flexibly change the capacitance detection circuit to expand its application scenarios.

Specifically, when the value of the capacitance C _TP on the screen is greater than the value of the programmable capacitance array Cs, the selector is connected to the capacitance detection circuit based on the large C _TP ; the value of the capacitance C _TP on the screen is smaller than the value of the programmable capacitance array Cs , the selector connects to the capacitance detection circuit based on small C _TP .

It should be noted that since capacitance detection technicians can know the approximate range of the C _TP value based on experience, an analog switch can also be used to realize the function of the selector in this embodiment. In this embodiment, the first embodiment based on The capacitance detection circuit of large C _TP and the capacitance detection circuit based on small C _TP in the fourth embodiment are examples, and its structure is as shown in Figure 13. Specifically, the selector 30 in this embodiment may include: first Switch 301, second switch 302, third switch 303 and fourth switch 304; wherein, the second bias voltage V2 is connected to the first charging switch 201 through the first switch 301, and the second bias voltage V2 is connected through the second switch 302 It is connected to the second charging switch 203 ; the first bias voltage V1 is connected to the first charging switch 201 through the third switch 303 , and the second bias voltage V2 is connected to the second charging switch 203 through the fourth switch 304 .

In practical applications, when the second switch 302 and the third switch 303 are closed and the first switch 301 and the fourth switch 304 are opened, the first capacitance detection circuit is connected; when the second switch 302 and the third switch 303 are opened, the first When the switch 301 and the fourth switch 304 are closed, the second capacitance detection circuit is connected.

It is worth mentioning that the selector in this embodiment can also be realized by numerical control. First, the value of C _TP is detected to determine its size, and then connected to different capacitance detection circuits.

Those of ordinary skill in the art can understand that the above-mentioned embodiments are specific examples for realizing the present invention, and in practical applications, various changes can be made to it in form and details without departing from the spirit and spirit of the present invention. scope.

Claims (8)

1. a kind of based on big C_TPCapacitive detection circuit, comprising：Electric capacity C on screen_TP, feedback capacity Cf and an operational amplifier；Its It is characterised by, described based on big C_TPCapacitive detection circuit also include：Programmable capacitor array Cs, the first charge switch, second Charge switch, the first change-over switch and the second change-over switch；Wherein, the C_TPValue more than the Cs value；

The C_TPOne end be connected with the first bias voltage by first charge switch, and pass through first change-over switch It is connected with the negative input end of the operational amplifier, the C_TPThe other end ground connection；

One end of the Cs is connected with the second bias voltage by second charge switch, and passes through second change-over switch It is connected with the negative input end of the operational amplifier, the other end ground connection of the Cs；

Wherein, first bias voltage is less than second bias voltage.

2. according to claim 1 based on big C_TPCapacitive detection circuit, it is characterised in that described based on big C_TPElectric capacity Detection circuit also includes：3rd charge switch, the 4th charge switch and the 3rd change-over switch；

One end of the Cf is by the 3rd charge switch ground connection, and passes through the 3rd change-over switch and the operation amplifier The negative input end connection of device, the other end of the Cf pass through the negative input end of the 4th charge switch and the operational amplifier Connection.

3. according to claim 1 based on big C_TPCapacitive detection circuit, it is characterised in that described based on big C_TPElectric capacity Detection circuit also includes：5th charge switch, the 6th charge switch, the 7th charge switch, the 4th change-over switch and the 5th conversion Switch；

One end of the Cf is by the 5th charge switch ground connection, and passes through the 4th change-over switch and the operation amplifier The negative input end connection of device；

The other end of the Cf connects the 3rd bias voltage Vs by the 6th charge switch, and is opened by the 5th conversion Close and be connected with the output end of the operational amplifier；

By the 7th charge switch connection between the negative input end of the operational amplifier and output end.

4. a kind of based on little C_TPCapacitive detection circuit, comprising：Electric capacity C on screen_TP, feedback capacity Cf and an operational amplifier；Its It is characterised by, described based on little C_TPCapacitive detection circuit also include：Programmable capacitor array Cs, the first charge switch, second Charge switch, the first change-over switch and the second change-over switch；Wherein, the C_TPValue less than the Cs value；

The C_TPOne end be connected with the second bias voltage by first charge switch, and pass through first change-over switch It is connected with the negative input end of the operational amplifier, the C_TPThe other end ground connection；

One end of the Cs is connected with the first bias voltage by second charge switch, and passes through second change-over switch It is connected with the negative input end of the operational amplifier, the other end ground connection of the Cs；

Wherein, first bias voltage is less than second bias voltage.

5. according to claim 4 based on little C_TPCapacitive detection circuit, it is characterised in that described based on little C_TPElectric capacity Detection circuit also includes：3rd charge switch, the 4th charge switch and the 3rd change-over switch；

One end of the Cf is by the 3rd charge switch ground connection, and passes through the 3rd change-over switch and the operation amplifier The negative input end connection of device, the other end of the Cf pass through the negative input end of the 4th charge switch and the operational amplifier Connection.

6. according to claim 4 based on little C_TPCapacitive detection circuit, it is characterised in that described based on little C_TPElectric capacity Detection circuit also includes：5th charge switch, the 6th charge switch, the 7th charge switch, the 4th change-over switch and the 5th conversion Switch；

One end of the Cf is by the 5th charge switch ground connection, and passes through the 4th change-over switch and the operation amplifier The negative input end connection of device；

The other end of the Cf connects the 3rd bias voltage Vs by the 6th charge switch, and is opened by the 5th conversion Close and be connected with the output end of the operational amplifier；

By the 7th charge switch connection between the negative input end of the operational amplifier and output end.

7. a kind of capacitance detecting device, it is characterised in that include：As described in any one in claims 1 to 3 based on big C_TP Capacitive detection circuit and as described in any one in claim 4 to 6 based on little C_TPCapacitive detection circuit, also include one Selector；

Electric capacity C on screen_TPValue of the value more than programmable capacitor array Cs when, selector connection is described to be based on big C_TPElectricity Hold detection circuit；

Electric capacity C on screen_TPValue of the value less than programmable capacitor array Cs when, selector connection is described to be based on little C_TPElectricity Hold detection circuit.

8. capacitance detecting device according to claim 7, it is characterised in that the selector includes：First switch, second Switch, the 3rd switch and the 4th switch；

Second bias voltage is connected with first charge switch by the first switch, and second bias voltage leads to Cross the second switch to be connected with second charge switch；

First bias voltage is connected with first charge switch by the 3rd switch, and second bias voltage leads to Cross the described 4th switch to be connected with second charge switch.