WO2017166058A1

WO2017166058A1 - Portable electronic device, capacitive touch screen, and capacitance detection circuit

Info

Publication number: WO2017166058A1
Application number: PCT/CN2016/077688
Authority: WO
Inventors: 蒋宏
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2016-03-29
Filing date: 2016-03-29
Publication date: 2017-10-05
Also published as: CN107466368A; CN107466368B

Abstract

Disclosed is a capacitance detection circuit, comprising: an amplifier, a dominant pole of the amplifier being controllable, and an inverting input end of the amplifier being configured to connect to capacitor to be detected; a feedback capacitor module connected between the inverting input end of the amplifier and an output end of the amplifier, the capacitance value of the feedback capacitor module being adjustable; a feedback resistor module connected between the inverting input end of the amplifier and the output end of the amplifier, the resistance value of the feedback resistor module being adjustable; and a capacitance calculation module connected to the output end of the amplifier and configured to detect a change in value of the capacitor to be detected according to an output signal of the amplifier. The capacitance detection circuit has a strong anti-interference capability, and can well achieve resistance to low-frequency interference and high-frequency interference. Also disclosed are a capacitive touch screen and a portable electronic device.

Description

Portable electronic device, capacitive touch screen and capacitance detecting circuit

Technical field

The present invention relates to the field of capacitance detection technology, and in particular to a capacitance detection circuit with strong anti-interference, a capacitive touch screen having the capacitance detection circuit, and a portable electronic device.

Background technique

With the increasing popularity of smartphones and tablets, capacitive touch technology has been widely used. At present, the basic principle of capacitive touch is to detect the change of capacitance. This capacitor has an open electric field, so that the proximity of the hand can have a significant influence on the size of the capacitor. In the capacitance detection technology using mutual capacitance, the hand close to this capacitor will decrease. In the capacitance detection technique using self-capacitance, the hand close to this capacitance will increase.

However, because of the open electric field of this capacitor, the LCD (Liquid Crystal Display) driving signal will be coupled in, and the common mode interference on the human body will be coupled when the hand is close. Mode interference will also be coupled by hand. These interferences will seriously affect the performance and function of capacitive touch. If the interference is not large, the SNR (Signal-to-Noise Ratio) of the capacitive touch will decrease. Touch accuracy and user experience, when the interference is serious, the capacitive touch will appear to point or jump, so the capacitive touch screen can not work, causing inconvenience to the user.

Summary of the invention

This application is based on the inventors' knowledge and research on the following issues:

In the related art, there is a capacitance detecting circuit 100 using a purely resistive feedback method. As shown in FIG. 1A, the greatest advantage of such a circuit is that it can form a zero point by using the capacitor 102 to be tested, and has low frequency interference for less than the minimum operating frequency f _l . It has a strong inhibitory effect, so it has a strong ability to resist low frequency interference. 1A and 1B, since the main pole frequency f _{c of the} amplifier 104 is usually much higher than the highest operating frequency f _h of the circuit, the circuit does not have any suppression capability for interference in the f _l to f _h band. And it will be amplified, the end result is that the circuit is very resistant to high-frequency interference, and this high-pass amplitude-frequency characteristic is easy to cause the amplifier output to saturate, reduce the available dynamic range of the amplifier, and also because of the amplification of high-frequency interference signals. This causes the aliasing problem of the ADC (Analog-to-Digital Converter), so this capacitor detection circuit needs at least two-stage low-pass filter to increase the number of stages, cost, power consumption and area. . In addition, due to the differential nature of such circuits, such circuits are not ideally driven by square wave signals.

Moreover, the inventors found in the study that the above-mentioned capacitance detecting circuit is not flat due to the amplitude-frequency response in its operating frequency band. Tan, the higher the operating frequency, the greater the signal gain. Therefore, for capacitance detection, the circuit detection performance can be improved by increasing the frequency. However, the capacitance on the capacitive touch screen has a high resistance characteristic and cannot actually work at a very high level. The frequency, so not only this advantage can not be reflected in the capacitive touch screen detection, but it becomes a shortcoming of anti-interference.

In the related art, there is also a capacitance detecting circuit using a full capacitance feedback method as shown in FIG. 2A. This circuit uses the charge characteristic of the feedback capacitor 203 to detect a change in the capacitor 202 to be tested. This detecting circuit is often called a charge. The amplifier, but since there is no DC feedback, a reset switch 206 is required to periodically reset the accumulation of the input bias current of the amplifier 204 on the feedback capacitor 203 to avoid saturation of the output of the amplifier. Also, such a circuit can usually be used only in an amplifier of a CMOS (Complementary Metal Oxide Semiconductor) process, and cannot be used in an amplifier using a Bipolar (Bipolar Transistor) process. As shown in Fig. 2A and Fig. 2B, from the frequency domain analysis, the circuit has no poles before the main pole frequency f _{c of the} amplifier, so it has a flat amplitude frequency response in the frequency band of 0 to f _l . Thus, the capacitance detecting circuit 200 does not have any suppression capability for low frequency and high frequency interference. However, in the working environment of the capacitive touch screen, the amplitude of the low frequency interference signal is usually large, mainly at 50 Hz and its higher harmonics; The high-frequency interference signal is mainly the LCD driving signal, and its amplitude is also large, and its fundamental wave or harmonic is in the working frequency band of the capacitive touch screen. Therefore, the actual performance of the capacitance detecting circuit 200 used on the capacitive touch screen is poor.

The present invention aims to solve at least one of the technical problems in the above-mentioned techniques to some extent. To this end, the first object of the present invention is to provide a capacitance detecting circuit with strong anti-interference ability, which can well achieve low-frequency interference and high-frequency interference resistance.

A second object of the present invention is to provide a capacitive touch screen. A third object of the present invention is to provide a portable electronic device.

In order to achieve the above object, a capacitance detecting circuit according to a first aspect of the present invention includes: an amplifier, a main pole of the amplifier is controllable, an inverting input end of the amplifier is used to connect a capacitor to be tested; and a feedback capacitor a module, the feedback capacitance module is connected between an inverting input end of the amplifier and an output end of the amplifier, and a capacitance value of the feedback capacitance module is adjustable; a feedback resistance module, the feedback resistance module is connected in the Between the inverting input terminal of the amplifier and the output end of the amplifier, the resistance of the feedback resistor module is adjustable; the capacitance calculation module, the capacitance calculation module is connected to the output end of the amplifier, and the capacitance calculation The module is configured to detect a change in capacitance of the capacitance to be tested according to an output signal of the amplifier.

The capacitance detecting circuit according to the embodiment of the invention adopts a feedback mode combining an adjustable feedback resistor and an adjustable feedback capacitor to add a controllable pole to the whole circuit, thereby canceling each other with the zero point generated by the capacitor to be tested, and the controllable pole After that, the amplitude-frequency response becomes flat, so that after the main pole frequency of the amplifier, the higher the frequency, the lower the amplitude, and the performance against low-frequency interference and high-frequency interference can effectively prevent the amplifier saturation problem caused by the interference. Increase The circuit can use dynamic range and SNR. And by controlling the main pole of the amplifier, it is adapted to the working frequency band corresponding to the capacitive touch, thereby achieving the anti-interference performance and the SNR performance optimal.

According to an embodiment of the invention, the main pole frequency of the amplifier is greater than the highest operating frequency of the capacitance detecting circuit, and the difference between the main pole frequency and the highest operating frequency is less than a preset value.

According to an embodiment of the invention, the main pole frequency of the amplifier varies following the highest operating frequency of the capacitance detecting circuit.

According to an embodiment of the invention, the feedback capacitance module and the feedback resistance module jointly generate a controllable pole, and the frequency corresponding to the controllable pole changes between the lowest operating frequency and the highest operating frequency of the capacitance detecting circuit. .

According to an embodiment of the invention, the first operating frequency band of the capacitance detecting circuit is between a frequency corresponding to a pole generated by the feedback capacitance module and the feedback resistance module and a frequency of a main pole of the amplifier.

According to an embodiment of the invention, the capacitance detecting circuit has a uniform amplitude-frequency characteristic in the first operating frequency band.

According to another embodiment of the invention, the second operating frequency band of the capacitance detecting circuit is between the lowest operating frequency and the highest operating frequency of the capacitance detecting circuit.

The highest operating frequency of the capacitance detecting circuit is smaller than the comparison frequency, and the comparison frequency is a frequency corresponding to the controllable pole generated by the feedback capacitance module and the feedback resistance module, and a frequency of a main pole of the amplifier. The lower one.

According to an embodiment of the invention, the amplifiers are arranged independently or by separate transistor devices.

According to an embodiment of the invention, the feedback capacitance module is a capacitance variable continuously variable capacitor, or the feedback capacitance module comprises a plurality of parallel first capacitance branches, each of the first capacitance branches comprising a series connection A switch and a first feedback capacitor.

According to an embodiment of the invention, the feedback resistance module is a resistance variable continuously variable resistor, or the feedback resistance module comprises a plurality of parallel first resistance branches, each of the first resistance branches comprising a series connection The second switch and the first feedback resistor.

According to an embodiment of the invention, when the amplifier is the fully differential amplifier, the fully differential amplifier has a non-inverting input, an inverting input, a non-inverting output, an inverting output, and an output common mode voltage control. End, the capacitance detecting circuit further includes a first feedback resistor array, a first feedback capacitor array, a first resistor and an offset voltage control terminal, wherein the first feedback resistor array is connected to the non-inverting input terminal and the opposite Between the phase output terminals, the first feedback capacitor array is connected in parallel with the first feedback resistor array, and the non-inverting input terminal is connected to the offset voltage control terminal through the first resistor, and the feedback capacitor module is connected in The feedback resistor module is connected in parallel with the feedback capacitor module between the inverting input terminal and the non-inverting output terminal.

The first feedback capacitor array includes a plurality of parallel second capacitor branches, each of the second capacitor branches includes a third switching switch and a second feedback capacitor connected in series, and the first feedback resistor array includes a plurality of A second resistor branch in parallel, each second resistor branch comprising a fourth switch in series and a second feedback resistor.

According to another embodiment of the present invention, when the amplifier is the fully differential amplifier, the fully differential amplifier has a non-inverting input, an inverting input, a non-inverting output, an inverting output, and an output common mode voltage. a control terminal, the capacitance detecting circuit further includes a second feedback resistor array, a second feedback capacitor array, and a first capacitor, wherein the second feedback resistor array is connected to the non-inverting input terminal and the inverting output terminal The second feedback capacitor array is connected in parallel with the second feedback resistor array, the non-inverting input is grounded through the first capacitor, and the feedback capacitor module is connected to the inverting input terminal and the non-inverting output. Between the terminals, the feedback resistor module is connected in parallel with the feedback capacitor module.

The second feedback capacitor array includes a plurality of parallel third capacitor branches, each third capacitor branch includes a fifth switching switch and a third feedback capacitor connected in series, and the second feedback resistor array includes a plurality of A third resistor branch connected in parallel, each third resistor branch comprising a sixth switching switch and a third feedback resistor connected in series.

In an embodiment of the invention, the capacitance detecting circuit has a band pass characteristic.

In order to achieve the above object, another embodiment of the present invention further provides a capacitive touch screen including the above-described capacitance detecting circuit.

According to the capacitive touch screen of the embodiment of the invention, the capacitance detecting circuit can have strong anti-interference ability when being touched, and has high touch precision, good user experience, and stable and reliable operation.

Moreover, embodiments of the present invention also provide a portable electronic device that includes the capacitive touch screen described above.

The portable electronic device of the embodiment of the invention not only has a sensitive and smooth touch, but also does not appear to be a point or a jump point when the touch is performed, thereby improving the user experience and fully satisfying the needs of the user.

DRAWINGS

1A and FIG. 1B are respectively a schematic diagram of a capacitance detecting circuit using a pure resistance feedback method and a corresponding amplitude-frequency response curve diagram in the related art;

2A and 2B are respectively a schematic diagram of a capacitance detecting circuit using a full capacitance feedback method and a corresponding amplitude frequency response curve diagram in the related art;

3A and 3B are respectively a schematic diagram of a capacitance detecting circuit and a corresponding amplitude-frequency response graph according to an embodiment of the invention;

4 is a schematic diagram of a capacitance detecting circuit according to a first embodiment of the present invention;

FIG. 5 is a schematic diagram of a capacitance detecting circuit according to a second embodiment of the present invention; FIG.

Figure 6 is a schematic diagram of a capacitance detecting circuit in accordance with a third embodiment of the present invention.

detailed description

The embodiments of the present invention are described in detail below, and the examples of the embodiments are illustrated in the drawings, wherein the same or similar reference numerals are used to refer to the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the drawings are intended to be illustrative of the invention and are not to be construed as limiting.

A capacitance detecting circuit, a capacitive touch screen having the capacitance detecting circuit, and a portable electronic device according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 3A and FIG. 3B, the capacitance detecting circuit 300 of the embodiment of the present invention includes an amplifier 304, a feedback capacitance module 303, a feedback resistance module 306, and a capacitance calculation module 305.

The main pole of the amplifier 304 is controllable, and the inverting input end of the amplifier 304 is connected to the capacitor 302 to be tested, that is, the second end connected to the capacitor Cx to be tested. The first end of the capacitor Cx to be tested is connected to the driving circuit 301, and the amplifier 304 The non-inverting input is grounded. The feedback capacitor module 303 is connected between the inverting input of the amplifier 304 and the output of the amplifier 304, and the capacitance of the feedback capacitor module 303 is adjustable. The feedback resistor module 306 is connected to the inverting input of the amplifier 304 and the amplifier 304. The feedback resistor module 306 is connected in parallel with the feedback capacitor module 303, and the resistance of the feedback resistor module 306 is adjustable. The capacitance calculation module 305 is connected to the output end of the amplifier 304. The capacitance calculation module 305 is configured to detect the capacitance change of the capacitance 302 to be tested according to the output signal of the amplifier 304, thereby implementing the capacitance detection function.

That is, as shown in FIG. 3A and FIG. 3B, the capacitance detecting circuit 300 of the embodiment of the present invention uses a feedback mode in which a capacitance value adjustable feedback capacitance module 303 and a resistance value adjustable resistance feedback module 306 are combined, The control circuit adds a controllable pole, that is, the feedback capacitor module 303 and the feedback resistor module 306 together generate a controllable pole, and the frequency corresponding to the control pole is between the lowest operating frequency f _{l of the} capacitance detecting circuit and the highest operating frequency f _h The variation, as shown in FIG. 3B, is such that the zero point generated by the capacitor 302 to be tested cancels each other such that the amplitude-frequency response after the controllable pole becomes flat, and the frequency is higher after the main pole frequency f _{c of the} amplifier 304. The lower.

According to an embodiment of the present invention, the first operating frequency band of the capacitance detecting circuit 300 is between the frequency corresponding to the controllable pole generated by the feedback resistor module 306 and the feedback capacitor module 303 and the main pole frequency f _{c of the} amplifier 304. And the capacitance detecting circuit 300 has a uniform amplitude frequency characteristic in the first working frequency band, as shown in FIG. 3B. Therefore, the interference in the frequency band lower than the controllable pole frequency generated by the feedback resistor module 306 and the feedback capacitor module 303 is suppressed, and the lower the frequency, the stronger the suppression performance, and the interference in the frequency band higher than the main pole frequency of the amplifier The signal is also suppressed, and the higher the frequency is suppressed, and the operating frequency of the capacitance detecting circuit of the embodiment of the present invention can be easily changed due to the uniform amplitude-frequency response in the operating band of the circuit. Design brings convenience.

Wherein, when the driving signal outputted by the driving circuit 301 is a square wave signal, the capacitance detecting circuit generally operates in the first working frequency band.

According to another embodiment of the invention, the second operating frequency band of the capacitance detecting circuit is between the lowest operating frequency f _{l of the} capacitance detecting circuit and the highest operating frequency f _h . Moreover, the highest operating frequency f _{h of} the capacitance detecting circuit is smaller than the comparison frequency, and the comparison frequency is the lower of the frequency corresponding to the controllable pole generated by the feedback capacitance module and the feedback resistance module and the main pole frequency of the amplifier. Thus, when the capacitance detecting circuit of the embodiment of the present invention operates in the second operating frequency band, it has the highest signal gain at each operating frequency, and since the capacitance detecting circuit has the highest signal gain, the capacitance detecting circuit Has better SNR characteristics.

Wherein, when the driving signal outputted by the driving circuit 301 is a sine wave signal, the capacitance detecting circuit generally operates in the second working frequency band.

In summary, the suppression function of the low-frequency interference signal of the capacitance detecting circuit 300 of the embodiment of the present invention makes the low-frequency interference signal unable to enter the circuit, and the suppression of the low-frequency large-value interference such as the power frequency can significantly improve the dynamic range available to the circuit; The frequency detecting characteristic of the capacitance detecting circuit 300 of the embodiment makes the high frequency interference signal unable to enter the circuit, and can also improve the dynamic range of the circuit, reduce the problem of aliasing of the ADC, or reduce the anti-aliasing filter for the ADC. The order of the order.

It should be noted that, in general, the amplifier used in the capacitance detecting circuit generally has a high main pole, for example, several Mhz or several tens of Mhz, but when the capacitance detecting circuit of the embodiment of the present invention is used on the capacitive touch IC, Due to the characteristics of the capacitive touch control, the capacitance detecting circuit is required to operate in a frequency band of only several hundred Khz, so that the interference in the frequency band of several hundred Khz to the main pole frequency of the amplifier cannot be attenuated. Therefore, the embodiment of the present invention The amplifier in the capacitance detection circuit needs to be specially designed. In other words, in order to match the operating frequency band of the capacitive touch screen and achieve optimal anti-interference characteristics, the main pole frequency of the amplifier in the capacitance detecting circuit of the embodiment of the invention is optimally set at the highest operating frequency of the capacitive touch, so that the height is high. The interference signal also has an attenuation effect in the frequency band of the capacitive touch screen operating frequency and lower than the main pole frequency of the amplifier.

Therefore, in an embodiment of the invention, the main pole frequency of amplifier 304 follows the highest operating frequency of the capacitance sensing circuit. Moreover, the main pole frequency of the amplifier is greater than the highest operating frequency of the capacitance detecting circuit, and the difference between the main pole frequency and the highest operating frequency is less than a preset value. That is to say, the main pole frequency of the amplifier needs to be slightly larger than the highest operating frequency of the capacitance detecting circuit, and varies with the change of the highest operating frequency, and is always satisfied to be slightly larger than the highest operating frequency.

In summary, the capacitance detecting circuit of the embodiment of the present invention can exhibit strong low frequency and high frequency anti-interference performance, improve the available dynamic range of the circuit, and improve the overall performance of the capacitance detection.

In some embodiments of the present invention, the feedback capacitance module 303 may be a capacitor whose capacitance is continuously variable (ie, the capacitance of the capacitor may continuously change); or the feedback capacitance module 303 includes a plurality of first capacitive branches connected in parallel, each The first capacitive branch includes a first switching switch and a first feedback capacitor connected in series, that is, the capacitance of the feedback capacitance module 303 is discontinuously changed. Moreover, the feedback resistor module 306 is a resistor whose resistance value is continuously variable (ie, the resistance of the resistor can be continuously changed); or the feedback resistor module 306 includes a plurality of first resistor branches connected in parallel, each of the first resistor branches The second switching switch connected in series and the first feedback resistor, that is, the resistance of the feedback resistor module 306 is discontinuously changed.

Specifically, according to the first embodiment of the present invention, as shown in FIG. 4, the capacitance detecting circuit 400 includes a standard operational amplifier 404, a plurality of first feedback capacitors 403 connected in series, and a plurality of first switching switches 407, A plurality of first feedback resistors 406 and a plurality of second switching switches 408 are connected in series, and a capacitance calculation module 405. One end of the capacitor 402 to be tested is connected to the output of the driving circuit 401, and the other end of the capacitor 402 to be tested is connected to the inverting input terminal of the standard operational amplifier 404, and the non-inverting input terminal of the standard operational amplifier 404 is grounded. Each of the first feedback capacitors 403 and the corresponding first switch 407 constitute a first capacitive branch, and each of the first feedback resistors 406 and the corresponding second switch 408 constitute a first resistance branch, and the plurality of first capacitor branches The circuits are connected in parallel, a plurality of first resistor branches are connected in parallel, and a plurality of first capacitor branches connected in parallel and a plurality of first resistor branches connected in parallel are connected in parallel to the inverting input terminal and the output terminal of the standard operational amplifier 404. Between, thus forming a negative feedback. The output of the standard operational amplifier 404 is coupled to a capacitance calculation module 405.

The specific working principle of the capacitance detecting circuit 400 is that the driving circuit 401 generates a driving waveform, which may be a square wave, a sine wave or a triangular wave. Taking the most common sine wave as an example, the output of the driving circuit 401 is an input of the circuit. The output of operational amplifier 404 has a transfer function:

Where R _fb is the feedback resistor and C _fb is the feedback capacitor.

It can be seen from the above transfer function that the circuit has a zero-zero starting point, so the capacitance detecting circuit 400 has a high-pass characteristic, but the circuit introduces a circuit at f=1/2πR _fb C _fb due to the existence of the feedback capacitance C _fb . The pole, and thus the zero and pole of the circuit, cancels, so that the capacitance detection circuit 400 exhibits a flat frequency response, but since the operational amplifier will have a pole fc at a higher frequency, the frequency portion of the circuit exceeding fc exhibits a low-pass characteristic. . Wherein, as long as the zero point formed by the feedback capacitor and the feedback resistor is set to be slightly higher than the highest operating frequency of the capacitance detecting circuit 400, the signal in the operating frequency band is not affected, and is higher than the zero point formed by the feedback capacitor and the feedback resistor. The high-frequency interference will not be amplified, so the whole circuit behaves as a band-pass characteristic, which can effectively filter out high-frequency and low-frequency interference, improve the effective dynamic range of the circuit, and improve the overall performance of the capacitance detection.

Moreover, in an embodiment of the present invention, the amplifiers may be independently provided, that is, a separate amplifying device; The amplifier may alternatively be an amplifying device of separate transistor devices, i.e., a plurality of separate devices together form an amplifying device that is amplified as a whole. Therein, in some examples of the invention, the amplifier can be a fully differential amplifier.

Preferably, according to the second embodiment of the present invention, when the amplifier is a fully differential amplifier, the fully differential amplifier has a non-inverting input, an inverting input, a non-inverting output, an inverting output, and an output common mode voltage control terminal, The capacitance detecting circuit further includes a first feedback resistor array, a first feedback capacitor array, a first resistor and an offset voltage control terminal, wherein the first feedback resistor array is connected between the non-inverting input terminal and the inverting output terminal, the first feedback The capacitor array is connected in parallel with the first feedback resistor array, and the non-inverting input terminal is connected to the offset voltage control terminal through the first resistor, and the feedback capacitor module is connected between the inverting input terminal and the non-inverting output terminal, and the feedback resistor module is connected in parallel with the feedback capacitor module. The first feedback capacitor array includes a plurality of parallel second capacitor branches, each of the second capacitor branches includes a third switching switch and a second feedback capacitor connected in series, and the first feedback resistor array includes a plurality of parallel second A resistor branch, each of the second resistor branches including a fourth switch in series and a second feedback resistor.

Specifically, as shown in FIG. 5, the capacitance detecting circuit 500 includes a fully differential amplifier 510, a plurality of first feedback capacitors 403 and a plurality of first switching switches 407, a plurality of first feedback resistors 406 connected in series, and a plurality of a second switching switch 408, a plurality of second feedback capacitors 503 and a plurality of third switching switches 507, a plurality of second feedback resistors 506 and a plurality of fourth switching switches 508, a first resistor 509, and an offset voltage control End 504, capacitance calculation module 512. The fully differential amplifier 510 has an output common mode voltage control terminal 505, two output ports, namely, a non-inverting output terminal 513 and an inverting output terminal 511, which are output in a fully differential manner. Of course, the capacitance calculation module 512 in this embodiment also has differential signal processing capability, which will not be described here. Each of the second feedback capacitors 503 and the corresponding third switch 507 constitutes a second capacitor branch, and each of the second feedback resistors 506 and the corresponding fourth switch 508 form a second resistor branch. The second capacitor branch forms a first capacitor array in parallel, and the plurality of second resistor branches are connected in parallel to form a first resistor array.

The working principle of the capacitance detecting circuit 500 is similar to that of the first embodiment, and will not be described herein. The first feedback resistor 406 and the second feedback resistor 506 typically have the same resistance value, and typically have the same capacitance value for the first feedback capacitor 403 and the second feedback capacitor 503. The resistor 509 can generally be used to control the gain of the capacitance detecting circuit 500. The first feedback resistor 406 and the second feedback resistor 506 can also be used to control the gain of the circuit, the capacitor 502 to be tested and the first feedback resistor 406 and the second feedback resistor. 506 will form a zero point, which actually starts from zero, so the circuit will exhibit high-pass characteristics; the addition of the first feedback capacitor 403 and the second feedback capacitor 503 will form with the first feedback resistor 406 and the second feedback resistor 506. A controllable pole such that a zero and a pole of the capacitance detecting circuit 500 cancel each other out, so that the circuit exhibits a flat amplitude frequency response. Since the fully differential amplifier 510 has a main pole, the band circuit exceeding this main pole will exhibit a low-pass characteristic, so that the capacitance detecting circuit 500 of the present embodiment exhibits a band pass characteristic and is resistant to low frequency and High frequency interference, boost circuit available dynamic range Encircle and improve the overall performance of the capacitance test.

With respect to the capacitance detecting circuit 400 in the first embodiment, since the capacitance detecting 500 in the present embodiment employs a fully differential amplifier, there is an advantage that the dynamic range of the output voltage is doubled, so that a higher circuit dynamic range can be obtained.

Preferably, according to the third embodiment of the present invention, when the amplifier is a fully differential amplifier, the fully differential amplifier has a non-inverting input terminal, an inverting input terminal, a non-inverting output terminal, an inverting output terminal, and an output common mode voltage control terminal. The detecting circuit further includes a second feedback resistor array, a second feedback capacitor array and a first capacitor, wherein the second feedback resistor array is connected between the non-inverting input terminal and the inverting output terminal, and the second feedback capacitor array and the second feedback resistor The array is connected in parallel, and the non-inverting input terminal is grounded through the first capacitor, and the feedback capacitor module is connected between the inverting input terminal and the non-inverting output terminal, and the feedback resistor module is connected in parallel with the feedback capacitor module. The second feedback capacitor array includes a plurality of parallel third capacitive branches, each of the third capacitive branches includes a fifth switching switch and a third feedback capacitor connected in series, and the second feedback resistor array includes a plurality of parallel connected third A resistor branch, each of the third resistor branches including a sixth switch in series and a third feedback resistor.

Specifically, as shown in FIG. 6, the capacitance detecting circuit 600 includes a fully differential amplifier 610, a plurality of first feedback capacitors 403 and a plurality of first switching switches 407, a plurality of first feedback resistors 406 connected in series, and a plurality of a second switch 408, a plurality of third feedback capacitors 603 and a plurality of fifth switch 607, a plurality of third feedback resistors 606 and a plurality of sixth switch 608, a first capacitor 609, and a capacitance calculation module 612. The fully differential amplifier 610 has an output common mode voltage control terminal 605, two output ports, namely, a non-inverting output terminal 613 and an inverting output terminal 611, which are output in a fully differential manner. Of course, the capacitance calculation module 612 in this embodiment also has differential signal processing capability, which will not be described here. Each of the third feedback capacitors 603 and the corresponding fifth switch 607 constitutes a third capacitor branch, and each of the third feedback resistors 606 and the corresponding sixth switch 608 form a third resistor branch. The third capacitor branch forms a second capacitor array in parallel, and the plurality of third resistor branches are connected in parallel to form a second resistor array. Also, the non-inverting input of the fully differential amplifier 610 is coupled to ground through a first capacitor 609.

Compared with the second embodiment, in the capacitance detecting circuit 600 of the present embodiment, the capacitor 609 is used instead of the resistor 509 in the capacitance detecting circuit 500 of the second embodiment, and the capacitance detecting circuit of the second embodiment is removed. The offset control terminal 504 in 500 is directly grounded. The other circuit configuration is exactly the same as that of the capacitance detecting circuit 500 in the second embodiment described above. Therefore, in the capacitance detecting circuit 600 of the embodiment, when the feedback resistor 406 and the feedback resistor 606 are equal, the feedback capacitor 403 and the feedback capacitor 603 are equal, the capacitor 609 and the capacitor 602 to be tested are equal, and the entire circuit is in a fully differential form. Therefore, the circuit has an optimum SNR characteristic, and since the entire circuit is in a fully differential form, the capacitance detecting circuit of the present embodiment has a large suppression effect on the common mode noise inside the amplifier 610, and is output common mode. The common mode noise of the voltage control terminal 605 has a good suppression effect, and since one end of the capacitor 609 is connected to the ground, the circuit does not need an offset voltage control terminal, and a noise contribution source is eliminated. Therefore, the output of the capacitance detecting circuit 600 of the present embodiment has lower noise, higher SNR, and other properties remain unchanged.

In addition, an embodiment of the present invention also provides a capacitive touch screen including the capacitance detection described in the above embodiment. Circuit.

Finally, embodiments of the present invention also provide a portable electronic device that includes the capacitive touch screen described above. The portable electronic device may be an electronic device such as a mobile phone or a tablet computer.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " After, "Left", "Right", "Vertical", "Horizontal", "Top", "Bottom", "Inside", "Outside", "Clockwise", "Counterclockwise", "Axial", The orientation or positional relationship of the "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is merely for convenience of description of the present invention and simplified description, and does not indicate or imply the indicated device or component. It must be constructed and operated in a particular orientation, and is not to be construed as limiting the invention.

Moreover, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, features defining "first" or "second" may include at least one of the features, either explicitly or implicitly. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless specifically defined otherwise.

In the present invention, the terms "installation", "connected", "connected", "fixed" and the like shall be understood broadly, and may be either a fixed connection or a detachable connection, unless explicitly stated and defined otherwise. , or integrated; can be mechanical or electrical connection; can be directly connected, or indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction of two elements, unless otherwise specified Limited. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood on a case-by-case basis.

In the present invention, the first feature "on" or "under" the second feature may be a direct contact of the first and second features, or the first and second features may be indirectly through an intermediate medium, unless otherwise explicitly stated and defined. contact. Moreover, the first feature "above", "above" and "above" the second feature may be that the first feature is directly above or above the second feature, or merely that the first feature level is higher than the second feature. The first feature "below", "below" and "below" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely that the first feature level is less than the second feature.

In the description of the present specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means a specific feature described in connection with the embodiment or example. A structure, material or feature is included in at least one embodiment or example of the invention. In the present specification, the schematic representation of the above terms is not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or features described may be It is combined in a suitable manner in any one or more embodiments or examples. In addition, various embodiments or examples described in the specification, as well as features of various embodiments or examples, may be combined and combined.

Although the embodiments of the present invention have been shown and described, it is understood that the above-described embodiments are illustrative and are not to be construed as limiting the scope of the invention. The embodiments are subject to variations, modifications, substitutions and variations.

Claims

A capacitance detecting circuit, comprising:

An amplifier whose main pole is controllable, and an inverting input of the amplifier is used to connect a capacitor to be tested;

a feedback capacitance module, the feedback capacitance module is connected between an inverting input end of the amplifier and an output end of the amplifier, and a capacitance value of the feedback capacitance module is adjustable;

a feedback resistor module, the feedback resistor module is connected between an inverting input end of the amplifier and an output end of the amplifier, and a resistance value of the feedback resistor module is adjustable;

a capacitance calculation module, the capacitance calculation module is connected to an output end of the amplifier, and the capacitance calculation module is configured to detect a capacitance change of the capacitance to be tested according to an output signal of the amplifier.
The capacitance detecting circuit according to claim 1, wherein said amplifier is independently provided or constituted by a separate transistor device.
The capacitance detecting circuit according to claim 1, wherein said feedback capacitance module is a capacitor whose capacitance value is continuously variable, or said feedback capacitance module comprises a plurality of first capacitive branches connected in parallel, each first The capacitor branch includes a first switch in series and a first feedback capacitor.
The capacitance detecting circuit according to claim 1, wherein said feedback resistance module is a resistance variable continuously variable resistor, or said feedback resistance module comprises a plurality of parallel first resistance branches, each of said A resistor branch includes a second switch in series and a first feedback resistor.
The capacitance detecting circuit according to claim 2, wherein said fully differential amplifier has a non-inverting input, an inverting input, an in-phase output, an inverting output, and an output when said amplifier is a fully differential amplifier a common mode voltage control terminal, the capacitance detecting circuit further includes a first feedback resistor array, a first feedback capacitor array, a first resistor, and an offset voltage control terminal, wherein the first feedback resistor array is connected to the non-inverting input terminal And the first feedback capacitor array is connected in parallel with the first feedback resistor array, and the non-inverting input terminal is connected to the offset voltage control terminal through the first resistor, the feedback A capacitor module is coupled between the inverting input terminal and the non-inverting output terminal, and the feedback resistor module is coupled in parallel with the feedback capacitor module.
The capacitance detecting circuit according to claim 5, wherein said first feedback capacitance array comprises a plurality of parallel second capacitive branches, each second capacitive branch comprising a third switching switch and a second in series a feedback capacitor, the first feedback resistor array includes a plurality of parallel second resistor branches, each second resistor branch including a fourth switching switch and a second feedback resistor connected in series.
The capacitance detecting circuit according to claim 2, wherein said fully differential amplifier has a non-inverting input, an inverting input, an in-phase output, an inverting output, and an output when said amplifier is a fully differential amplifier a common mode voltage control terminal, the capacitance detecting circuit further includes a second feedback resistor array, a second feedback capacitor array, and a first capacitor, The second feedback resistor array is connected between the non-inverting input terminal and the inverting output terminal, the second feedback capacitor array is connected in parallel with the second feedback resistor array, and the non-inverting input terminal passes through The first capacitor is grounded, the feedback capacitor module is connected between the inverting input terminal and the non-inverting output terminal, and the feedback resistor module is connected in parallel with the feedback capacitor module.
The capacitance detecting circuit according to claim 7, wherein said second feedback capacitance array comprises a plurality of parallel third capacitive branches, each third capacitive branch comprising a fifth switching switch and a third in series a feedback capacitor, the second feedback resistor array includes a plurality of parallel third resistor branches, each of the third resistor branches including a sixth switching switch and a third feedback resistor connected in series.
The capacitance detecting circuit according to any one of claims 1 to 8, wherein a main pole frequency of the amplifier is greater than a highest operating frequency of the capacitance detecting circuit, and the main pole frequency and the highest operation are The difference between the frequencies is less than the preset value.
The capacitance detecting circuit according to claim 1, wherein a main pole frequency of said amplifier changes in accordance with a highest operating frequency of said capacitance detecting circuit.
The capacitance detecting circuit of claim 1 , wherein the feedback capacitance module and the feedback resistance module together generate a controllable pole, the frequency corresponding to the control pole being at a minimum operating frequency of the capacitance detecting circuit Change with the highest operating frequency.
The capacitance detecting circuit according to claim 11, wherein a frequency of the first operating frequency band of the capacitance detecting circuit corresponding to a pole generated by the feedback capacitance module and the feedback resistance module is opposite to a frequency of the amplifier Between the main pole frequencies.
The capacitance detecting circuit according to claim 12, wherein said capacitance detecting circuit has uniform amplitude-frequency characteristics in said first operating frequency band.
The capacitance detecting circuit according to claim 11, wherein a second operating frequency band of said capacitance detecting circuit is between a lowest operating frequency and a highest operating frequency of said capacitance detecting circuit.
The capacitance detecting circuit according to claim 14, wherein a maximum operating frequency of the capacitance detecting circuit is smaller than a comparison frequency, and the comparison frequency is a controllable pole jointly generated by the feedback capacitance module and the feedback resistance module The lower of the corresponding frequency and the main pole frequency of the amplifier.
The capacitance detecting circuit according to any one of claims 1 to 15, wherein the capacitance detecting circuit has a band pass characteristic.
A capacitive touch screen, comprising the capacitance detecting circuit according to any one of claims 1-16.
A portable electronic device comprising the capacitive touch screen of claim 17.