Piezoelectric ceramic apparatus for static force measurement, and electronic device

Abstract

Disclosed in the present application are a piezoelectric ceramic apparatus for static force measurement, and an electronic device. The piezoelectric ceramic apparatus for static force measurement comprises a charge amplifier, a processing unit, a piezoelectric sensor and a first reference voltage end, wherein the piezoelectric sensor is used for detecting a differential electrical signal which is generated when a pressing region of a touchpad is pressed with a static force, and inputting same into the charge amplifier; the charge amplifier is used for outputting an output voltage corresponding to the static force after receiving the differential electrical signal; the processing unit is used for measuring the output voltage of the charge amplifier, and outputting a reset signal to the charge amplifier when detecting that the output voltage is lower than a bias voltage; and the charge amplifier further comprises a reset circuit, which is electrically connected to the processing unit, and is used for restoring the output voltage to the bias voltage after receiving the reset signal. Thus, a charge amplifier can be prevented from generating noise during actual operation that interferes with a measurement result of a piezoelectric sensor.

Description

Piezoelectric ceramic static force detection device and electronic equipment TECHNICAL FIELD

[0001] The present application relates to the technical field of force measurement, in particular to a piezoelectric ceramic static force detection device and electronic equipment. BACKGROUND

[0002] In some electronic devices, a touchpad is usually configured as an interactive input device to interact with the user. A piezoelectric sensor, as an important sensor device of the touchpad, is used to detect the pressing force applied by the user on the touchpad and convert it into a sensing signal, which is provided to a processing unit for processing. The piezoelectric sensor is a sensor based on the piezoelectric effect, and its sensitive element is made of piezoelectric material (such as piezoelectric ceramic). The piezoelectric sensor can convert the measured force, acceleration and other parameters applied on the touchpad into changes in charge or voltage parameters for output by using the piezoelectric effect of the piezoelectric material.

[0003] Since the internal impedance of the piezoelectric sensor is very high, and the output signal is very weak, it cannot be directly displayed and recorded, and it cannot be measured as a static signal. Therefore, a high input impedance preamplifier is often needed as an impedance matching to prevent the rapid leakage of the electric charge generated on the surface of the piezoelectric material due to stress, thereby reducing measurement errors. The preamplifier of the piezoelectric sensor has two functions: impedance conversion and amplification of the weak signal output by the piezoelectric sensor. The output signal can be voltage or charge. Therefore, the preamplifier also has two forms: one is a voltage amplifier, and the other is a charge amplifier. Because the voltage amplifier has a simple circuit, fewer components, lower price and more reliable work compared with the charge amplifier, the voltage amplifier is generally used as the preamplifier of the piezoelectric sensor in the measurement circuit of the piezoelectric sensor for detecting static force in the application of the touchpad. However, the sensitivity and anti-interference ability of the voltage amplifier are not as good as those of the charge amplifier. Therefore, the piezoelectric sensor static force detection device using the voltage amplifier as the preamplifier has the defect of not being sensitive to the slow pressing or slight pressing of the touchpad.

[0004] SUMMARY

[0005] The embodiments of the present application aim to provide a piezoelectric ceramic static force detection device and electronic equipment, which can overcome the defect of the existing piezoelectric sensor static force detection device that is not sensitive to the slow pressing or slight pressing of the touchpad.

[0006] To solve the above technical problems, the first aspect of the present application provides a piezoelectric ceramic static force detection device, which comprises a charge amplifier, a processing unit, a piezoelectric sensor and a first reference voltage terminal; the charge amplifier is electrically connected with the piezoelectric sensor, the processing unit and the first reference voltage terminal respectively; wherein:

[0007] The piezoelectric sensor is used to detect the differential electric signal generated when the pressing area of the touchpad is pressed by a static force, and input the differential electric signal to the charge amplifier;

[0008] The charge amplifier is used to output an output voltage corresponding to the static force when receiving the differential electric signal input by the piezoelectric sensor;

[0009] The processing unit is used to detect the output voltage of the charge amplifier, and output a reset signal to the charge amplifier when detecting that the output voltage is lower than a bias voltage; wherein the bias voltage is a first reference voltage from the first reference voltage terminal;

[0010] The charge amplifier further comprises a reset circuit, which is electrically connected with the processing unit and used to restore the output voltage to the bias voltage when receiving the reset signal output by the processing unit.

[0011] In one of the embodiments, the charge amplifier further comprises an operational amplifier, a feedback circuit and a filter circuit; wherein:

[0012] The operational amplifier comprises an inverting input terminal, a non-inverting input terminal and an output terminal, and the inverting input terminal and the non-inverting input terminal are electrically connected with two ends of the piezoelectric sensor respectively, and used to receive the electric signal input by the piezoelectric sensor;

[0013] The feedback circuit is electrically connected with the inverting input terminal and the output terminal of the operational amplifier respectively, and used to feed back the output voltage of the output terminal of the operational amplifier to the inverting input terminal of the operational amplifier, and compensate the inverting input terminal of the operational amplifier;

[0014] The filter circuit is electrically connected with the non-inverting input terminal of the operational amplifier and the first reference voltage terminal respectively, and used to form a bias voltage by filtering the first reference voltage of the first reference voltage terminal, and introduce the bias voltage to the non-inverting input terminal of the operational amplifier, and use the bias voltage as the output voltage of the output terminal of the operational amplifier when no electric signal input by the piezoelectric sensor is received;

[0015] The reset circuit is electrically connected with the processing unit and the operational amplifier respectively, and is configured to restore the output voltage of the output end of the operational amplifier to the bias voltage when receiving a reset signal output from the processing unit.

[0016] In one of the embodiments, the feedback circuit comprises a first resistor and a first capacitor, a first end of the first resistor and a first end of the first capacitor are electrically connected, and then electrically connected with the inverting input end of the operational amplifier, a second end of the first resistor and a second end of the first capacitor are electrically connected, and then electrically connected with the output end of the operational amplifier.

[0017] In one of the embodiments, the filter circuit comprises a second resistor and a second capacitor, a first end of the second resistor and a first end of the second capacitor are electrically connected, and then electrically connected with the non-inverting input end of the operational amplifier, a second end of the second resistor and a second end of the second capacitor are electrically connected, and then electrically connected with the first reference voltage end.

[0018] In one of the embodiments, the reset circuit comprises a first transistor and a second transistor; wherein:

[0019] The base of the first transistor receives a reset signal applied from the processing unit, the emitter of the first transistor is electrically connected with the first end of the first resistor, the first end of the first capacitor and the inverting input end of the operational amplifier respectively, and the collector of the first transistor is electrically connected with the second end of the first resistor, the second end of the first capacitor and the output end of the operational amplifier respectively.

[0020] The base of the second transistor receives a reset signal applied from the processing unit, the emitter of the second transistor is electrically connected with the first end of the second resistor, the first end of the second capacitor and the non-inverting input end of the operational amplifier respectively, and the collector of the second transistor is electrically connected with the second end of the second resistor, the second end of the second capacitor and the first reference voltage end respectively.

[0021] In one of the embodiments, the reset circuit comprises a third MOS tube, a fifth resistor, a fourth MOS tube and a sixth resistor; wherein:

[0022] The gate of the third MOS tube receives a first reset signal applied from the processing unit, the source of the third MOS tube is grounded, and the drain of the third MOS tube is electrically connected with the first end of the first resistor, the first end of the first capacitor and the inverting input end of the operational amplifier through the fifth resistor respectively;

[0023] The gate of the fourth MOS receives a second reset signal applied from the processing unit, the drain of the fourth MOS is electrically connected with the first end of the second resistor, the first end of the second capacitor and the non-inverting input of the operational amplifier through the sixth resistor respectively, and the source of the fourth MOS is electrically connected with the second reference voltage terminal.

[0024] In one of the embodiments, the charge amplifier further comprises a first low-pass filter electrically connected with the inverting input of the operational amplifier and the piezoelectric sensor respectively, for low-pass filtering the electric signal of the piezoelectric sensor input to the inverting input of the operational amplifier.

[0025] In one of the embodiments, the first low-pass filter comprises a third resistor and a third capacitor, the first end of the third resistor is electrically connected with the piezoelectric sensor, the second end of the third resistor is electrically connected with the first end of the third capacitor and then electrically connected with the inverting input of the operational amplifier, and the second end of the third capacitor is grounded.

[0026] In one of the embodiments, the charge amplifier further comprises a second low-pass filter electrically connected with the non-inverting input of the operational amplifier and the piezoelectric sensor respectively, for low-pass filtering the electric signal of the piezoelectric sensor input to the non-inverting input of the operational amplifier.

[0027] In one of the embodiments, the second low-pass filter comprises a fourth resistor and a fourth capacitor, the first end of the fourth resistor is electrically connected with the piezoelectric sensor, the second end of the fourth resistor is electrically connected with the first end of the fourth capacitor and then electrically connected with the non-inverting input of the operational amplifier, and the second end of the fourth capacitor is grounded.

[0028] In one of the embodiments, the processing unit is further configured to compensate the output voltage of the charge amplifier, specifically: judging whether the output voltage of the charge amplifier is greater than a trigger threshold, if yes, further judging whether the difference between the current time constant and the last time constant is less than a time constant error threshold, if yes, compensating the output voltage of the charge amplifier, and if no, giving up compensating the output voltage of the charge amplifier.

[0029] Correspondingly, the second aspect embodiment of the present application provides an electronic device, which comprises the piezoelectric ceramic static force detection device of the first aspect embodiment of the present application.

[0030] The piezoelectric ceramic static force detection device and the electronic device provided by the present application comprise: a charge amplifier, a processing unit, a piezoelectric sensor and a first reference voltage terminal; the charge amplifier is electrically connected with the piezoelectric sensor, the processing unit and the first reference voltage terminal respectively; wherein: the piezoelectric sensor is used for detecting the differential electric signal generated when the pressing area of the touchpad is pressed by a static force, and inputting the differential electric signal to the charge amplifier; the charge amplifier is used for outputting the output voltage corresponding to the static force when receiving the differential electric signal input by the piezoelectric sensor; the processing unit is used for detecting the output voltage of the charge amplifier, and outputting the reset signal to the charge amplifier when detecting that the output voltage is lower than the bias voltage; wherein, the bias voltage is the first reference voltage from the first reference voltage terminal; the charge amplifier further comprises a reset circuit, which is electrically connected with the processing unit and is used for restoring the output voltage to the bias voltage when receiving the reset signal output by the processing unit. The static force detection device provided by the present application adopts the charge amplifier as the preamplifier of the piezoelectric sensor, which is used for detecting and amplifying the differential signal generated when the static force is applied to the piezoelectric sensor, and can overcome the defect that the existing piezoelectric sensor static force detection device using the voltage amplifier as the preamplifier is not sensitive to the slow pressing or the pressing with small force on the touchpad, and the charge amplifier is provided with the reset circuit electrically connected with the processing unit, which outputs the reset signal when the processing unit detects that the output voltage of the charge amplifier is lower than the bias voltage, so that the reset circuit of the charge amplifier restores the output voltage to the bias voltage when receiving the reset signal. Thus, the charge amplifier can be reset in advance every time the piezoelectric signal is measured, so as to avoid the influence of the measurement result of the piezoelectric sensor on the next measurement result, avoid the noise generated by the charge amplifier in the actual working process from affecting the measurement result of the piezoelectric sensor, improve the response sensitivity of the electronic device and improve the user experience. Thus, the defect that the existing piezoelectric sensor static force detection device is not sensitive to the slow pressing or the pressing with small force on the touchpad can be overcome. BRIEF DESCRIPTION OF DRAWINGS

[0031] One or more embodiments are illustrated by way of example in the figures that form a part of this patent document, and in which like reference numbers indicate similar elements as those found in several views of the drawings in which:

[0032] FIG. 1 is a schematic diagram of voltage variation of an existing piezoelectric sensor in an ideal working mode during pressure detection;

[0033] FIG. 2 is a schematic diagram of voltage variation of an existing piezoelectric sensor in an actual working mode during pressure detection;

[0034] Fig. 3 is a structural schematic diagram of a piezoelectric ceramic static force detection device provided by the present application;

[0035] Fig. 4 is a structural schematic diagram of a charge amplifier in a piezoelectric ceramic static force detection device provided by the present application;

[0036] Fig. 5 is a circuit schematic diagram of a charge amplifier in a piezoelectric ceramic static force detection device provided by the present application;

[0037] Fig. 6 is another circuit schematic diagram of a charge amplifier in a piezoelectric ceramic static force detection device provided by the present application;

[0038] Fig. 7 is a voltage variation schematic diagram of a piezoelectric ceramic static force detection device provided by the present application after reset by a reset circuit and compensation by an algorithm of a processing unit;

[0039] Fig. 8 is a structural schematic diagram of an electronic device provided by the present application.

[0040] Main component symbol explanation:

[0041] Charge amplifier 1 Processing amplifier U1

[0042] Feedback circuit 11 Filter circuit 12

[0043] Reset circuit 13 First low-pass filter 14

[0044] Piezoelectric sensor Y1 Second low-pass filter 15

[0045] First resistor R1 Second resistor R2

[0046] Third resistor R3 Fourth resistor R4

[0047] Fifth resistor R5 Sixth resistor R6

[0048] First capacitor C1 Second capacitor C2

[0049] Third capacitor C3 Fourth capacitor C4

[0050] First triode T1 Second triode T2

[0051] Third MOS transistor T3 Fourth MOS transistor T4

[0052] Piezoelectric ceramic static force detection device 10 Processing unit 2

[0053] Electronic device 100 DETAILED DESCRIPTION

[0054] For the purpose of promoting the understanding of the present application, the present application will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or one or more intervening elements can be present therebetween. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or one or more intervening elements can be present therebetween. The terms "upper", "lower", "inner", "outer", "bottom", and the like as used in this specification refer to the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are merely used for the purpose of facilitating the description of the present application and simplifying the description, and therefore should not be construed as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present application. In addition, the terms "first", "second", "third", and the like are merely used for the purpose of description and should not be construed as indicating or implying relative importance.

[0055] Unless otherwise defined, all technical and scientific terms used in the present specification are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the present specification are merely intended for the purpose of describing specific embodiments of the present application and are not intended to limit the present application. The term "and / or" as used in the present specification includes any and all combinations of one or more of the associated listed items.

[0056] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0057] In some electronic devices, a touchpad is usually configured as an interactive input device to interact with a user. A piezoelectric sensor is an important sensor device of the touchpad, which is used to detect the pressing force applied by the user on the touchpad and convert it into a sensing signal, which is provided to a processing unit for processing. The piezoelectric sensor is a sensor based on the piezoelectric effect, and the sensitive element thereof is made of piezoelectric material (such as piezoelectric ceramic). The piezoelectric sensor can convert the measured force, acceleration and other parameters applied on the touchpad into the change of electric charge or voltage parameter by using the piezoelectric effect of the piezoelectric material, and then output.

[0058] Since the internal impedance of the piezoelectric sensor is very high, and the output signal is very weak, it cannot be directly displayed and recorded, and it cannot be measured as a static signal. Therefore, a high input impedance preamplifier is often needed as an impedance matching in the measurement circuit to prevent the rapid leakage of the electric charge generated on the surface of the piezoelectric material due to force, thereby reducing the measurement error. The preamplifier of the piezoelectric sensor has two functions: one is impedance conversion, and the other is amplifying the weak signal output by the piezoelectric sensor. The output signal can be voltage or electric charge. Therefore, the preamplifier also has two forms: one is a voltage amplifier, and the other is a charge amplifier. Since the voltage amplifier is simpler in circuit, fewer components, cheaper in price and more reliable in operation compared with the charge amplifier, the voltage amplifier is generally used as the preamplifier of the piezoelectric sensor in the measurement circuit for detecting static force in the touchpad application. However, the sensitivity and anti-interference ability of the voltage amplifier are not as good as those of the charge amplifier. Therefore, the piezoelectric sensor static force detection device using the voltage amplifier as the preamplifier has the defect of not being sensitive enough in detecting the slow pressing or the pressing with small force on the touchpad in the application of the touchpad business scenario.

[0059] Therefore, the present application provides a piezoelectric ceramic static force detection device, which comprises a charge amplifier, a processing unit, a piezoelectric sensor comprising piezoelectric ceramic as piezoelectric material, and a first reference voltage terminal.

[0060] It should be noted that when the sensitive element of the piezoelectric sensor is made of piezoelectric ceramic, when the piezoelectric ceramic is in a compressed state (pressed state), the upper surface of the piezoelectric ceramic accumulates positive charges to generate a positive voltage, and the lower surface also accumulates positive charges to generate a positive voltage; on the contrary, when the piezoelectric ceramic is in a stretched state (released state), the piezoelectric ceramic will generate an opposite voltage, that is, the upper surface of the piezoelectric ceramic accumulates negative charges to generate a negative voltage, and the lower surface also accumulates negative charges to generate a negative voltage. That is, in the pressed state, the piezoelectric sensor can only generate a positive voltage, and when released, the piezoelectric sensor generates a negative charge to make the current voltage zero. And according to the theory of action and reaction, the force in the pressing process is equal to the force in the releasing process, so the absolute values of the charges generated by pressing and releasing are equal and the directions are opposite. Since the capacitance value of the piezoelectric sensor is fixed, according to the formula between voltage U and charge Q: U = Q / C, the voltage values generated by pressing and releasing the piezoelectric sensor are equal and the directions are opposite. The voltage (charge) generated by the piezoelectric sensor can be detected by the charge amplifier.

[0061] As shown in FIG. 1, in the normal pressure detection state of the piezoelectric sensor, when the piezoelectric sensor detects that the pressing area of the touchpad is pressed, the voltage generated by the piezoelectric sensor rises sharply, and then remains for a period of time, until the piezoelectric sensor detects that the pressing area of the touchpad is released and is not pressed, the voltage generated by the piezoelectric sensor drops sharply, that is, the case of first rising, maintaining, and then falling, there is no case of first falling and then rising. This is the ideal working mode of the piezoelectric sensor. However, there is no ideal operational amplifier circuit that can perfectly detect the piezoelectric sensor signal in the above ideal working mode. Because the input impedance of the operational amplifier is not infinite, and there is noise in the circuit.

[0062] The charge amplifier actually used in industry comprises a feedback resistor Rf and a feedback capacitor Cf, and the output signal of the piezoelectric sensor in the actual working mode when the piezoelectric sensor is used as a preamplifier in pressure detection is shown in FIG. 2. As shown in FIG. 2, when the piezoelectric sensor detects that the pressing area of the touchpad is pressed, the voltage generated by the piezoelectric sensor will be abruptly lifted. However, the traditional charge amplifier is usually a single-ended charge amplifier (comprising a feedback resistor Rf and a feedback capacitor Cf connected in parallel with the feedback resistor Rf) in design. The electronic components and the circuit structure of the single-ended charge amplifier are prone to generate a lot of noise in work, and the noise will be integrated all the time, which will cause the charge accumulated in the feedback capacitor Cf to be gradually discharged when the charge amplifier works, resulting in the change of the voltage signal output by the charge amplifier. As shown in FIG. 2, after the voltage generated by the piezoelectric sensor is abruptly lifted from the bias voltage, the output voltage signal will gradually decrease as the charge accumulated in the feedback capacitor Cf is gradually discharged. When the piezoelectric sensor detects that the pressing area of the touchpad is released and is not pressed, the voltage generated by the piezoelectric sensor will be abruptly lowered, and even the voltage will be abruptly lowered to below the bias voltage in the measurement circuit of the piezoelectric sensor. Therefore, the traditional charge amplifier applied in the piezoelectric sensor static force detection device will have the defect of unreliable work, which will affect the next measurement result of the piezoelectric sensor in the piezoelectric sensor static force detection device and affect the response sensitivity of the electronic equipment.

[0063] In order to overcome the defect, the charge amplifier designed in the present application is a differential amplifier, which can effectively suppress noise. In order to improve the reliability of the charge amplifier in the measurement circuit, the charge amplifier further comprises a reset circuit, which is electrically connected with the processing unit in the detection device, and is used to restore the output voltage output by the charge amplifier to the same bias voltage as the first reference voltage provided by the first reference voltage terminal when receiving the reset signal output from the processing unit, so that the charge amplifier can be reset in advance every time the piezoelectric signal is measured, avoiding the influence of the measurement result of the piezoelectric sensor on the next measurement result.

[0064] In order to facilitate the understanding of the above application concept of the present application, the above application concept of the present application will be described in more detail in combination with the drawings and specific embodiments.

[0065] In one embodiment, as shown in FIG. 3, the present application provides a piezoelectric ceramic static force detection device, which comprises a charge amplifier 1, a processing unit 2, a piezoelectric sensor Y1 and a first reference voltage terminal V1. The charge amplifier 1 is electrically connected with the piezoelectric sensor Y1, the processing unit 2 and the first reference voltage terminal V1 respectively. Wherein:

[0066] The piezoelectric sensor Y1 is configured to detect a differential electric signal generated when a pressing area of the touchpad is pressed by a static force, and input the differential electric signal to the charge amplifier 1.

[0067] The charge amplifier 1 is configured to output an output voltage corresponding to the static force when receiving the differential electric signal input by the piezoelectric sensor Y1, wherein the charge amplifier 1 is a differential charge amplifier.

[0068] The processing unit 2 is configured to detect the output voltage of the charge amplifier 1, and output a reset signal to the charge amplifier 1 when detecting that the output voltage is lower than a bias voltage, wherein the bias voltage is a first reference voltage from the first reference voltage terminal V1.

[0069] The charge amplifier further comprises a reset circuit 13 electrically connected to the processing unit 2, and configured to restore the output voltage to the bias voltage when receiving the reset signal output by the processing unit 2.

[0070] In the embodiment, a piezoelectric ceramic static force detection device is provided, which comprises a charge amplifier, a processing unit, a piezoelectric sensor, and a first reference voltage terminal. The charge amplifier is electrically connected to the piezoelectric sensor, the processing unit, and the first reference voltage terminal, respectively. The piezoelectric sensor is configured to detect a differential electric signal generated when a pressing area of the touchpad is pressed by a static force, and input the differential electric signal to the charge amplifier. The charge amplifier is configured to output an output voltage corresponding to the static force when receiving the differential electric signal input by the piezoelectric sensor. The processing unit is configured to detect the output voltage of the charge amplifier, and output a reset signal to the charge amplifier when detecting that the output voltage is lower than a bias voltage. The bias voltage is a first reference voltage from the first reference voltage terminal. The charge amplifier further comprises a reset circuit electrically connected to the processing unit, and configured to restore the output voltage to the bias voltage when receiving the reset signal output by the processing unit. Thus, the output voltage corresponding to the static force can be output when the pressing area of the touchpad is pressed by the static force, so that the processing unit outputs the reset signal when detecting that the output voltage is lower than the bias voltage, and the reset circuit of the charge amplifier restores the output voltage to the bias voltage when receiving the reset signal. Thus, the charge amplifier can be reset in advance every time the piezoelectric signal is measured, so as to avoid the influence of the measurement result of the piezoelectric sensor on the next measurement result, avoid the noise generated in the actual working process of the charge amplifier from affecting the measurement result of the piezoelectric sensor, improve the response sensitivity of the electronic device, and improve the user experience. Thus, the defect that the existing piezoelectric sensor static force detection device is not sensitive to slow pressing or slight pressing of the touchpad is overcome.

[0071] In one embodiment, the piezoelectric sensor Y1 is used to detect the differential electric signal generated when the pressing area of the touchpad is pressed by static force, and input the signal to the charge amplifier 1.

[0072] Specifically, the sensing element of the piezoelectric sensor Y1 is made of piezoelectric ceramic. The piezoelectric sensor Y1 is installed on the back of the pressing area of the touchpad. The piezoelectric ceramic of the piezoelectric sensor Y1 can also be fixed on the surface, and the top directly presses the surface of the pressing area, with no gap between the piezoelectric ceramic and the surface of the pressing area. Alternatively, the piezoelectric ceramic of the piezoelectric sensor Y1 can also be fixed on the surface, and the top is separated from the surface of the pressing area by a layer of silicone or hard foam.

[0073] For example, the piezoelectric sensor Y1 can be directly pasted on the back of the pressing area. If the pressing area is a plastic injection part, the piezoelectric ceramic of the piezoelectric sensor Y1 can also be injection molded into the plastic part.

[0074] When the pressing area of the touchpad is pressed by static force, electric charges can be accumulated on the upper and lower surfaces of the piezoelectric sensor Y1. The differential electric signal output between the two plates of the piezoelectric sensor Y1 can be measured, and the differential electric signal can be input to the charge amplifier 1.

[0075] In one embodiment, the charge amplifier 1 is used to output an output voltage corresponding to the static force when receiving the differential electric signal input by the piezoelectric sensor Y1.

[0076] The processing unit 2 is used to detect the output voltage of the charge amplifier 1, and output a reset signal B to the charge amplifier 1 when detecting that the output voltage is lower than the bias voltage; wherein the bias voltage is the first reference voltage from the first reference voltage terminal V1.

[0077] Specifically, the charge amplifier 1 is used to output the first reference voltage provided by the first reference voltage terminal as the bias voltage when not receiving the differential electric signal input by the piezoelectric sensor Y1, and output the bias voltage as the output voltage VOUT of the output terminal; output an output voltage corresponding to the static force when receiving the electric signal input by the piezoelectric sensor Y1, and restore the output voltage VOUT of the output terminal to the bias voltage when receiving the reset signal B applied by the processing unit 2.

[0078] Specifically, as shown in FIG. 4, the charge amplifier 1 further includes an operational amplifier U1, a feedback circuit 11, and a filter circuit 12; wherein:

[0079] The operational amplifier U1 includes an inverting input end and a non-inverting input end, and an output end VOUT, the inverting input end and the non-inverting input end are electrically connected to two ends of the piezoelectric sensor Y1 respectively, for receiving the differential electric signal input by the piezoelectric sensor Y1;

[0080] The feedback circuit 11 is electrically connected to the inverting input end and the output end OUT of the operational amplifier U1 respectively, for feeding back the output voltage VOUT of the output end OUT of the operational amplifier U1 to the inverting input end of the operational amplifier U1, and compensating the inverting input end of the operational amplifier U1.

[0081] The filter circuit 12 is electrically connected to the non-inverting input end of the operational amplifier U1 and the first reference voltage end V1 respectively, for filtering the first reference voltage provided by the first reference voltage end V1 as a bias voltage introduced to the non-inverting input end of the operational amplifier U1, and taking the bias voltage as the output voltage VOUT of the output end of the operational amplifier U1 when no differential electric signal input by the piezoelectric sensor Y1 is received.

[0082] The reset circuit 13 is electrically connected to the processing unit 2 and the operational amplifier U1 respectively, for restoring the output voltage VOUT of the output end of the operational amplifier U1 to the bias voltage when the reset signal B output from the processing unit 2 is received.

[0083] In the embodiment, when the differential electric signal input by the piezoelectric sensor Y1 is received by the operational amplifier U1, and the output voltage VOUT of the output end of the charge amplifier 1 is lower than the bias voltage when collected by the processing unit 2, the processing unit 2 applies the reset signal B to the reset circuit 13, so that the reset circuit 13 restores the output voltage VOUT of the operational amplifier U1 lower than the bias voltage to the bias voltage when the reset signal output from the processing unit is received. Thus, the problem that the existing charge amplifier generates noise in the actual working process, causes the change of the output voltage signal, and affects the response sensitivity of the electronic equipment can be solved.

[0084] In one embodiment, the feedback circuit 11 is electrically connected to the inverting input end and the output end OUT of the operational amplifier U1 respectively, for feeding back the output voltage VOUT of the output end OUT of the operational amplifier U1 to the inverting input end of the operational amplifier U1, and compensating the inverting input end of the operational amplifier U1, so as to ensure the stable operation of the operational amplifier U1.

[0085] Specifically, as shown in FIG. 5 and FIG. 6, the feedback circuit 11 comprises: a first resistor R1 and a first capacitor C1 connected in parallel, a first end of the first resistor R1 and a first end of the first capacitor C1 are electrically connected and then connected to the inverting input terminal of the operational amplifier U1, a second end of the first resistor R1 and a second end of the first capacitor C1 are electrically connected and then connected to the output terminal OUT of the operational amplifier U1.

[0086] As shown in FIG. 5 and FIG. 6, a first resistor R1 is connected between the output terminal OUT and the inverting input terminal of the operational amplifier U1, and a first capacitor C1 is connected in parallel on the first resistor R1. In the case that the resistance value of the first resistor R1 is extremely large, according to Kirchhoff's law, the charge Q1 accumulated by the first capacitor C1 is equal to the charge Qin generated by the piezoelectric sensor, i.e. Q1 = Qin. Therefore, VOUT = Q1 / C1 = -Qin / C1.

[0087] In the circuit shown in FIG. 5, the first resistor R1 functions to discharge the first capacitor C1. Since the charge amplifier will generate a lot of noise during the actual circuit operation, the charge amplifier will always integrate the noise, resulting in a change in the output voltage VOUT of the charge amplifier. However, if the resistance value of the first resistor R1 is too small, the stored charge in the first capacitor C1 will be quickly discharged, and the charge cannot be accumulated. In this case, the piezoelectric sensor cannot detect some low-frequency forces of slow pressing. Therefore, the first resistor R1 needs to be a relatively large resistance value, and the first resistor R1 cannot be in open circuit.

[0088] In the present embodiment, a first resistor R1 is connected between the output terminal OUT and the inverting input terminal of the operational amplifier U1, forming a negative feedback, which can ensure stable operation of the operational amplifier U1. In addition, a first capacitor C1 is connected in parallel on the first resistor R1, which can jointly constitute a low-pass filtering effect and a phase compensation effect, and can prevent the occurrence of self-excitation of the added zero point.

[0089] In one embodiment, the filter circuit 12 is electrically connected to the non-inverting input terminal of the operational amplifier U1 and the first reference voltage terminal V1 respectively, for introducing the first reference voltage of the first reference voltage terminal V1 as a bias voltage to the non-inverting input terminal of the operational amplifier U1, and taking the bias voltage as the output voltage VOUT of the output terminal of the operational amplifier U1 when no differential electrical signal input by the piezoelectric sensor Y1 is received.

[0090] Specifically, as shown in FIG. 5 and FIG. 6, the filter circuit 12 comprises: a second resistor R2 and a second capacitor C2, which are connected in parallel, a first end of the second resistor R2 and a first end of the second capacitor C2 are electrically connected and then connected to the non-inverting input terminal of the operational amplifier U1, a second end of the second resistor R2 and a second end of the second capacitor C2 are electrically connected and then connected to the first reference voltage terminal VI. For example, the reference voltage of the first reference voltage terminal VI is 1 / 6 VCC, and the reference voltage of the VCC is 3.3V.

[0091] In the filter circuit 12, the second resistor R2 functions to discharge the second capacitor C2. In order to keep the filter frequency of the filter circuit 12 consistent with that of the feedback circuit 11, the resistance value of the second resistor R2 is the same as that of the first resistor R1 of the feedback circuit 11, and the capacitance value of the second capacitor C2 is the same as that of the first capacitor C1 of the feedback circuit 11.

[0092] In one embodiment, the reset circuit 13 is electrically connected to the processing unit 2 and the operational amplifier U1, respectively, and is configured to restore the output voltage VOUT of the output terminal of the operational amplifier U1 to the bias voltage when receiving the reset signal B output from the processing unit 2.

[0093] Specifically, as an optional circuit embodiment, as shown in FIG. 5, the reset circuit 13 comprises: a first transistor T1 and a second transistor T2; wherein:

[0094] The base of the first transistor T1 receives the reset signal B applied from the processing unit 2, the emitter of the first transistor T1 is electrically connected to the first end of the first resistor R1, the first end of the first capacitor C1 and the inverting input terminal of the operational amplifier U1 in the feedback circuit 11, respectively, and the collector of the first transistor T1 is electrically connected to the second end of the first resistor R1, the second end of the first capacitor C1 and the output terminal OUT of the operational amplifier U1 in the feedback circuit, respectively.

[0095] The base of the second transistor T2 receives the reset signal B applied from the processing unit 2, the emitter of the second transistor T2 is electrically connected to the first end of the second resistor R2, the first end of the second capacitor C2 and the non-inverting input terminal of the operational amplifier U1 in the filter circuit 12, respectively, and the collector of the second transistor T2 is electrically connected to the second end of the second resistor R2, the second end of the second capacitor C2 in the filter circuit 12 and the first reference voltage terminal VI.

[0096] In the optional embodiment, when the pressing area of the touchpad is not pressed by static force, the operational amplifier U1 does not receive the electric signal input by the piezoelectric sensor Y1, the first transistor T1 and the second transistor T2 are cut off, the first reference voltage is applied to the non-inverting input terminal of the operational amplifier U1 as the bias voltage after being filtered by the filter circuit 12, and the output voltage VOUT of the operational amplifier U1 is kept constant. When the pressing area of the touchpad is pressed by static force, the operational amplifier U1 receives the electric signal input by the piezoelectric sensor Y1, outputs the output voltage VOUT corresponding to the static force and rapidly increases, in the process, the first capacitor C1 and the second capacitor C2 start to charge, since the static force pressing the pressing area of the touchpad is from small to large, the charging voltage of the first capacitor C1 and the second capacitor C2 is related to the size of the static force, the static force is instantaneously increased at the moment of pressing, the charging voltage of the first capacitor C1 and the second capacitor C2 is also increased, and the static force is constant at the moment of stable pressing, at which time the charging voltage of the first capacitor C1 and the second capacitor C2 is constant. After the static force is stable, the electric charge between the two ends of the piezoelectric sensor Y1 starts to decrease slowly, the first capacitor C1 starts to discharge through the first resistor R1, and the second capacitor C2 starts to discharge through the second resistor R2, so that the output voltage VOUT of the output terminal of the operational amplifier U1 is gradually reduced; when the static force applied to the pressing area of the touchpad is removed, the piezoelectric sensor Y1 is subjected to a reverse force, so that the piezoelectric sensor Y1 generates a reverse electric charge, and the voltage between the two ends of the first capacitor C1 and the second capacitor C2 is sharply reduced; in the process, the processor 2 detects the output voltage VOUT of the operational amplifier U1 in the charge amplifier 1 in real time, and outputs a reset signal B to the first transistor T1 and the second transistor T2 when it is detected that the output voltage VOUT of the operational amplifier U1 is lower than the bias voltage, so that the first transistor T1 and the second transistor T2 are turned on. When the first transistor T1 is turned on, the output terminal of the operational amplifier U1 is short-circuited with the inverting input terminal; when the second transistor T2 is turned on, the bias voltage is applied to the non-inverting input terminal of the operational amplifier U1, at which time, since the negative phase input terminal of the operational amplifier U1 is short-circuited with the output terminal of the operational amplifier U1, the input voltage of the negative phase input terminal is the output voltage VOUT of the operational amplifier U1, the output voltage VOUT of the operational amplifier U1 is lower than the bias voltage, i.e. the negative phase input terminal of the operational amplifier U1 is lower than the non-inverting input terminal, at which time, the output terminal of the operational amplifier U1 outputs the bias voltage as the output voltage VOUT, so as to restore the output voltage lower than the bias voltage to the bias voltage. After the output voltage lower than the bias voltage is restored to the bias voltage, the processing unit 2 disconnects the reset signal B applied to the base of the first transistor T1 and the base of the second transistor T2, controls the first transistor T1 and the second transistor T2 to be disconnected, and completes the fast reset process.

[0097] As an optional circuit embodiment, as shown in FIG. 6, the reset circuit 13 comprises a third MOS transistor T3, a fifth resistor R5, a fourth MOS transistor T4 and a sixth resistor R6; wherein:

[0098] The gate of the third MOS transistor T3 receives a first reset signal B1 applied from the processing unit 2, the source of the third MOS transistor T3 is grounded, and the drain of the third MOS transistor T3 is electrically connected to the first end of the first resistor R1 in the feedback circuit 11, the first end of the first capacitor C1 in the feedback circuit 11 and the inverting input terminal of the operational amplifier U1 through the fifth resistor R5, respectively. For example, the third MOS transistor T3 is an N-type MOS transistor.

[0099] The gate of the fourth MOS transistor T4 receives a second reset signal B2 applied from the processing unit 2; the drain of the fourth MOS transistor T4 is electrically connected to the first end of the second resistor R2 in the filter circuit 12, the first end of the second capacitor C2 in the filter circuit 12 and the non-inverting input terminal of the operational amplifier U1 through the sixth resistor R6, respectively, and the source of the fourth MOS transistor T4 is electrically connected to a second reference voltage terminal V2. For example, the fourth MOS transistor T4 is a P-type MOS transistor, and the reference voltage of the second reference voltage terminal V2 is 3.3V.

[0100] The first reset signal B1 and the second reset signal B2 applied by the processing unit 2 are both reset signals, wherein, since the third MOS transistor T3 is an N-type MOS transistor and the fourth MOS transistor T4 is a P-type MOS transistor, the second reset signal B2 is complementary to the first reset signal B1. For example, when the second reset signal B2 is high, the first reset signal B1 is low.

[0101] In the optional embodiment, when the pressing area of the touchpad is not pressed by static force, the operational amplifier U1 does not receive the electric signal input by the piezoelectric sensor Y1, the third MOS transistor T3 and the fourth MOS transistor T4 are cut off, the bias voltage formed by the first reference voltage is filtered by the filter circuit 12 and then applied to the non-inverting output terminal of the operational amplifier U1 as the output voltage VOUT of the operational amplifier U1, which remains constant. When the pressing area of the touchpad is pressed by static force, the operational amplifier U1 receives the electric signal input by the piezoelectric sensor Y1, outputs the output voltage VOUT corresponding to the static force and rapidly increases, in the process, the first capacitor C1 and the second capacitor C2 start to charge, since the static force pressing the pressing area of the touchpad increases from small to large, the charging voltage of the first capacitor C1 and the second capacitor C2 is related to the size of the static force, at the moment of pressing, the static force is instantaneously increased, the charging voltage of the first capacitor C1 and the second capacitor C2 is also increased, at the moment of stable pressing, the static force is constant, at this moment, the charging voltage of the first capacitor C1 and the second capacitor C2 is constant. After the static force is stable, the electric charge between the two ends of the piezoelectric sensor Y1 starts to decrease slowly, the first capacitor C1 starts to discharge through the first resistor R1, the second capacitor C2 starts to discharge through the second resistor R2, so that the output voltage VOUT of the output terminal of the charge amplifier 1 gradually decreases; when the static force applied to the pressing area of the touchpad is removed, the piezoelectric sensor Y1 is subjected to a reverse force, so that the piezoelectric sensor Y1 generates a reverse electric charge, so that the voltage between the two ends of the first capacitor C1 and the second capacitor C2 decreases sharply; in the process, the processor 2 detects the output voltage VOUT of the operational amplifier U1 in the charge amplifier 1 in real time, when it is detected that the output voltage VOUT of the operational amplifier U1 is lower than the bias voltage, the processor 2 applies a first reset signal B1 to the gate of the third MOS transistor T3 and a second reset signal B2 to the gate of the fourth MOS transistor T4. When the processing unit 2 applies the first reset signal B1 to the gate of the third MOS transistor T3 and the second reset signal B2 to the gate of the fourth MOS transistor T4, the third MOS transistor T3 and the fourth MOS transistor T4 are turned on, the power supply current passes through the fourth MOS transistor T4, the sixth resistor R6, the fourth resistor R4, the piezoelectric sensor Y1, the third resistor R3, the fifth resistor R5, the third MOS transistor T3 and then to the ground GND. At the same time, there is also a current from the output terminal VOUT of the operational amplifier U1 passing through the first resistor R1, the first capacitor C1, the fifth resistor R5, the third MOS transistor T3 and then to the ground GND.The process can quickly release the charge accumulated in the first capacitor C1 during use. At this time, since the negative phase input of the operational amplifier U1 is electrically connected to the output of the operational amplifier U1 through the feedback circuit composed of the first capacitor C1 and the first resistor R1, the output voltage VOUT of the operational amplifier U1 is lower than the bias voltage after the charge accumulated in the first capacitor C1 during use is released, so that the output voltage VOUT of the operational amplifier U1 is lower than the bias voltage. At this time, the output of the operational amplifier U1 outputs the bias voltage as the output voltage VOUT, so as to restore the output voltage lower than the bias voltage to the bias voltage. After the output voltage lower than the bias voltage is restored to the bias voltage, the processing unit 2 disconnects the first reset signal B1 applied to the gate of the third MOS tube T3 and the second reset signal B2 applied to the gate of the fourth MOS tube T4, controls the third MOS tube T3 and the fourth MOS tube T4 to be disconnected, and completes the fast reset process.

[0102] As shown in FIGS. 5 and 7, when the same phase input of the operational amplifier U1 does not receive the electric signal input by the piezoelectric sensor Y1 (i.e., the pressing area of the touchpad is not pressed by static force), the output OUT of the operational amplifier U1 outputs the bias voltage as the output voltage VOUT. When the same phase input of the operational amplifier U1 receives the electric signal input by the piezoelectric sensor Y1 (i.e., the pressing area of the touchpad is pressed by static force), the output voltage VOUT of the output OUT of the operational amplifier U1 is abruptly raised from the bias voltage (at this time, the output voltage VOUT is higher than the bias voltage). Since the charge amplifier generates a lot of noise during actual circuit operation, the charge amplifier will always integrate the noise, resulting in a change in the output voltage VOUT of the charge amplifier. The voltage generated when the piezoelectric sensor detects that the pressing area of the touchpad is pressed by static force is abruptly raised from the bias voltage. Before the pressing is released, the output voltage VOUT cannot always remain at the voltage at the time of voltage rise, but gradually decreases as the charge accumulated in the feedback capacitor Cf is gradually discharged. At the moment when the piezoelectric sensor detects that the pressing area of the touchpad is released, the negative charge generated by the piezoelectric sensor Y1 pulls the output voltage VOUT of the charge amplifier below the bias voltage, and the voltage generated by the piezoelectric sensor Y1 is abruptly lowered. At this time, the processing unit 2 collects the output voltage VOUT of the output of the operational amplifier U1 in real time, judges that the output voltage VOUT of the output of the operational amplifier U1 is lower than the bias voltage, and applies a reset signal B to the base of the first triode T1 and the base of the second triode T2, so as to turn on the first triode T1 and the second triode T2, and quickly restore the output voltage VOUT of the operational amplifier U1 lower than the bias voltage to the bias voltage.

[0103] In one embodiment, as shown in FIG. 4, the charge amplifier 1 further comprises a first low-pass filter 14 electrically connected to the inverting input terminal of the operational amplifier U1 and the piezoelectric sensor Y1 respectively, for low-pass filtering the differential voltage signal of the piezoelectric sensor Y1 input to the inverting input terminal of the operational amplifier U1.

[0104] Specifically, as shown in FIG. 5, the first low-pass filter 14 comprises a third resistor R3 and a third capacitor C3, a first end of the third resistor R3 is electrically connected to the piezoelectric sensor Y1, a second end of the third resistor R3 is electrically connected to a first end of the third capacitor C3, a second end of the third capacitor C3 is grounded, and a connection end where both the second end of the third resistor R3 and the first end of the third capacitor C3 are electrically connected is electrically connected to the inverting input terminal of the operational amplifier U1.

[0105] In one embodiment, as shown in FIG. 4, the charge amplifier 1 further comprises a second low-pass filter 15 electrically connected to the non-inverting input terminal of the operational amplifier U1 and the piezoelectric sensor Y1 respectively, for low-pass filtering the differential voltage signal of the piezoelectric sensor Y1 input to the non-inverting input terminal of the operational amplifier U1.

[0106] Specifically, as shown in FIG. 5, the second low-pass filter 15 comprises a fourth resistor R4 and a fourth capacitor C4, a first end of the fourth resistor R4 is electrically connected to the piezoelectric sensor Y1, a second end of the fourth resistor R4 is electrically connected to a first end of the fourth capacitor C4, a second end of the fourth capacitor C4 is grounded, and a connection end where both the second end of the fourth resistor R4 and the first end of the fourth capacitor C4 are electrically connected is electrically connected to the non-inverting input terminal of the operational amplifier U1.

[0107] In one embodiment, the processing unit 2 is further configured to compensate the output voltage VOUT of the charge amplifier 1 to obtain a compensated output voltage VOUT of the charge amplifier 1.

[0108] For example, the processing unit 2 has data processing capability and signal processing capability, and can be an integrated circuit chip, for example, the processing unit 2 can be a general-purpose processor, a DSP, an ASIC (Application Specific Integrated Circuit), or other programmable logic devices, etc., the general-purpose processor can be a microprocessor or any conventional processor, etc., for example, a SOC (System on Chip), an MCU (Microcontroller Unit), or a CPU.

[0109] As described above, taking Figure 5 as an example, when the touchpad's pressed area is pressed by a static force, charge accumulates on the upper and lower surfaces of the piezoelectric sensor Y1. This charge can be measured through the electrical signal output between the two plates of the piezoelectric sensor Y1, and the electrical signal is input into the charge amplifier 1. When the touchpad's pressed area is not pressed by a static force, the output voltage VOUT at the output end of the charge amplifier 1 is the bias voltage and remains constant. When the touchpad's pressed area is pressed by a static force, the output voltage VOUT at the output end of the charge amplifier 1 increases rapidly. This process is the charging stage of the first capacitor C1 and the second capacitor C2. Since the static force pressing the touchpad's pressed area increases from small to large, the charging voltages of the first capacitor C1 and the second capacitor C2 are related to the magnitude of the static force. The static force increases instantaneously at the moment of pressing, and the charging voltages of the first capacitor C1 and the second capacitor C2 also increase. When the pressing is stable, the static force is constant, and the charging voltages of the first capacitor C1 and the second capacitor C2 are constant. After the static force stabilizes, the charge across the piezoelectric sensor Y1 begins to slowly decrease, the first capacitor C1 begins to discharge through the first resistor R1, and the second capacitor C2 begins to discharge through the second resistor R2, gradually decreasing the output voltage VOUT reading at the output of the charge amplifier 1. During the lifting phase, relative to the application of a reverse force to the piezoelectric sensor Y1, the piezoelectric sensor Y1 is subjected to a reverse force, causing a reverse charge to appear on the piezoelectric sensor Y1, causing the voltage across the first capacitor C1 and the second capacitor C2 to drop sharply, pulling the charge amplifier voltage VOUT below the bias voltage, requiring compensation to measure the actual static force.

[0110] When the first capacitor C1 and the second capacitor C2 discharge, their discharge speed meets the discharge law of general capacitors. At the same time, the influence of the charge amplifier will be coupled into the discharge curve, but the main factor is the capacitor discharge curve. Taking Figure 5 as an example, since the first capacitor C1 and the second capacitor C2 are equivalent to a parallel relationship, the charge is charged into the first capacitor C1 and the second capacitor C2 at the same time; the first resistor R1 and the second resistor R2 are also equivalent to a parallel relationship. Therefore, the capacitor C is equivalent to the first capacitor C1 and the second capacitor C2, and the capacitance of the capacitor C is the sum of the capacitances of the first capacitor C1 and the second capacitor C2, that is, C = C1 + C2; the resistor R is equivalent to the first resistor R1 and the second resistor R2, and the resistance of the resistor R is the parallel resistance of the resistances of the first resistor R1 and the second resistor R2, that is, R = R1 * R2 / (R1 + R2).

[0111] Since the charge across the piezoelectric sensor Y1 starts to decrease slowly after the static force pressing the pressing area of the touchpad is stabilized, the capacitor C starts to discharge through the resistor R, so that the output voltage VOUT at the output end of the charge amplifier 1 is gradually reduced, therefore, the output voltage VOUT at the output end of the charge amplifier 1 needs to be compensated to keep the output voltage VOUT at the output end of the charge amplifier 1 at a stable reading. The discharge rate of the capacitor is related to the time constant τ, and the time constant τ = R*C. In the embodiment of the application, the discharge compensation is to fit the capacitor discharge curve by a compensation algorithm during the discharge of the capacitor, so that the capacitor discharge curve tends to be linear. Specifically, the discharged part is compensated back using the time constant τ and the time when the discharge starts, so as to achieve the purpose of discharge compensation.

[0112] For the time constant τ, both the charging and discharging stages are related to the time constant τ, but in the charging stage, since the force is variable, that is, the capacitor charging voltage is always changing, the time constant τ cannot be solved by the real-time voltage value, so the time constant τ cannot be solved in the charging stage. In the discharging stage, the force is constant at this time, the variable is time, and the unknown quantity is the time constant τ value, so the time constant τ value can be solved by sampling the voltage.

[0113] The discharge process of the capacitor C satisfies the following equation (1):

[0114] Umax is the voltage when the charging is completed, and t = 0 is the time when the charging is completed.

[0115] After the pressing area of the touchpad is pressed by the static force, the capacitor C starts to charge, and the voltage value of the capacitor C continuously rises. When the static force reaches a stable state, the voltage value of the capacitor C reaches a peak and no longer rises. Then, the capacitor C starts to discharge, that is, the peak value is the turning point. Before the peak point, the voltage value across the piezoelectric sensor continuously rises, and after the peak point, the voltage value continuously decreases. Therefore, the peak point can be used as an approximate estimate of the voltage Umax when the charging is completed. For the voltage sampling in the falling stage, a plurality of equations related to the time constant τ can be obtained. In the application, the voltage values at the time t1 after the charging is completed and at the time t1+Δt are taken as references, and the following equation (2) can be obtained to further solve the time constant τ.

[0116] After the time when the voltage Umax when the charging is completed and the estimated value of the time constant τ are obtained, the voltage Umax' can be estimated from the voltage value ui at any time ti in the discharging stage, as shown in the following equation (3), and the voltage value Umax' after the actual compensation is obtained, that is, the output voltage VOUT at the output end of the charge amplifier 1 after the compensation:

[0117] In summary, the processing unit 2 is used to compensate the output voltage VOUT of the output end of the charge amplifier 1 to obtain the compensated output voltage VOUT of the output end of the charge amplifier 1. Specifically, it is determined whether the output voltage VOUT of the output end of the charge amplifier 1 is greater than the trigger threshold. If it is greater, it is further determined whether the difference between the current time constant and the time constant at the last moment is less than the time constant error threshold. If the difference is less than the time constant error threshold, the output voltage VOUT of the charge amplifier 1 is compensated. If the difference is greater than or equal to the time constant error threshold, the compensation of the output voltage VOUT of the charge amplifier 1 is abandoned. Thus, after the compensation of the output voltage VOUT of the output end of the charge amplifier 1, the lifted output voltage can be maintained for a period of time until the piezoelectric sensor detects that the pressing area of the touchpad is released and is not pressed by a static force. The output voltage of the piezoelectric sensor drops sharply, so that the output voltage of the piezoelectric sensor first rises, then maintains, and then drops, thereby achieving a similar ideal working mode of the piezoelectric sensor. The piezoelectric sensor signal can be perfectly detected by the charge amplifier, the response sensitivity of the electronic device is improved, and the user experience is improved.

[0118] The processing unit 2 is used to compensate the output voltage VOUT of the output end of the charge amplifier 1 to obtain the compensated output voltage VOUT of the output end of the charge amplifier 1, specifically including:

[0119] S1, low-pass filtering the output voltage of the output end of the charge amplifier 1 to further remove high-frequency impact signals in the force application process.

[0120] S2, determining whether the output voltage after low-pass filtering is greater than the trigger threshold. If it is greater, step S3 of compensation judgment is executed.

[0121] S3, compensation judgment, determining whether the voltage after low-pass filtering is a rising edge or a falling edge. If it is a rising edge, the peak point time is recorded. If it is a falling edge, step S4 of the compensation phase is executed to start compensation.

[0122] S4, compensation phase, calculating the current time constant τ according to the above equation (2), and comparing whether the difference between the current time constant τ and the time constant τ at the last moment is less than the time constant τ error threshold. If the difference is less than the time constant τ error threshold, the output voltage VOUT of the charge amplifier 1 is compensated according to the above equation (3). If the difference is greater than or equal to the time constant τ error threshold, it is considered to be a lifting phase, and the compensation of the output voltage VOUT of the charge amplifier 1 is abandoned.

[0123] As shown in FIG. 7, when the piezoelectric sensor detects that the pressing area of the touchpad is pressed by static force, the voltage generated by the piezoelectric sensor rises sharply. After the processing unit of the piezoelectric ceramic static force detection device provided in the present application compensates the output voltage VOUT of the output end of the charge amplifier 1, the raised output voltage can be maintained for a period of time, until the piezoelectric sensor detects that the pressing area of the touchpad is not pressed by static force, and the output voltage generated by the piezoelectric sensor drops sharply. The output voltage of the piezoelectric sensor first rises, then maintains, and then drops, so as to achieve a mode similar to the ideal working mode of the piezoelectric sensor, so that the charge amplifier can perfectly detect the piezoelectric sensor signal, improve the response sensitivity of the electronic device, and improve the user experience.

[0124] Based on the same concept, as shown in FIG. 8, the present application also provides an electronic device 100, which comprises the piezoelectric ceramic static force detection device 10 described in any of the above embodiments.

[0125] In the present embodiment, the piezoelectric ceramic static force detection device 10 is consistent with the piezoelectric ceramic static force detection device 10 described in any of the above embodiments, and the specific structure and function can be referred to the piezoelectric ceramic static force detection device 10 described in any of the above embodiments, which will not be described here.

[0126] In the present embodiment, by providing an electronic device comprising a piezoelectric ceramic static force detection device, the piezoelectric ceramic static force detection device comprises: a charge amplifier, a processing unit, a piezoelectric sensor, and a first reference voltage end; the charge amplifier is electrically connected with the piezoelectric sensor, the processing unit, and the first reference voltage end respectively; wherein: the piezoelectric sensor is used to detect the differential electric signal generated when the pressing area of the touchpad is pressed by static force, and input the differential electric signal to the charge amplifier; the charge amplifier is used to output the output voltage corresponding to the static force when receiving the differential electric signal input by the piezoelectric sensor; the processing unit is used to detect the output voltage of the charge amplifier, and output the reset signal to the charge amplifier when detecting that the output voltage is lower than the bias voltage; wherein, the bias voltage is the first reference voltage from the first reference voltage end; the charge amplifier further comprises a reset circuit, which is electrically connected with the processing unit, and is used to restore the output voltage to the bias voltage when receiving the reset signal output from the processing unit. Thus, the charge amplifier can be reset in advance every time the piezoelectric signal is measured, so as to avoid the influence of the measurement result of the piezoelectric sensor on the next measurement result, avoid the noise generated in the actual working process of the charge amplifier to affect the measurement result of the piezoelectric sensor, improve the response sensitivity of the electronic device, and improve the user experience. Thus, the defect that the existing piezoelectric sensor static force detection device is not sensitive to slow pressing or slight pressing of the touchpad is overcome.

[0127] It should be noted that the above electronic device embodiment and the above piezoelectric ceramic static force detection device embodiment belong to the same concept, the specific implementation process is seen from the piezoelectric ceramic static force detection device embodiment, and the technical features in the piezoelectric ceramic static force detection device embodiment are all applicable in the above electronic device embodiment, which will not be repeated here.

[0128] It should be noted that in this paper, the term "includes", "contains" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, method, article or device. Without more limitations, the element defined by the sentence "includes a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0129] The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in details; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A piezoelectric ceramic static force detection device, characterized in that: The piezoelectric ceramic static force detection device includes a charge amplifier, a processing unit, a piezoelectric sensor, and a first reference voltage terminal; the charge amplifier is electrically connected to the piezoelectric sensor, the processing unit, and the first reference voltage terminal, respectively; wherein: The piezoelectric sensor is used to detect the differential electrical signal generated when the pressing area of ​​the touch panel is pressed by a static force, and input it into the charge amplifier; The charge amplifier is configured to output an output voltage corresponding to the static force when receiving the differential electrical signal input by the piezoelectric sensor; The processing unit is configured to detect the output voltage of the charge amplifier and output a reset signal to the charge amplifier when detecting that the output voltage is lower than a bias voltage; wherein the bias voltage is a first reference voltage from the first reference voltage terminal; The charge amplifier further includes a reset circuit, which is electrically connected to the processing unit and is configured to restore the output voltage to the bias voltage upon receiving a reset signal output from the processing unit.

2. The piezoelectric ceramic static force detection device according to claim 1, characterized in that: The charge amplifier further includes an operational amplifier, a feedback circuit and a filter circuit; wherein: The operational amplifier includes an inverting input terminal, a non-inverting input terminal and an output terminal, wherein the inverting input terminal and the non-inverting input terminal are electrically connected to two ends of the piezoelectric sensor respectively, and are used to receive the electrical signal input by the piezoelectric sensor; The feedback circuit is electrically connected to the inverting input terminal and the output terminal of the operational amplifier, respectively, and is used to feed back the output voltage of the output terminal of the operational amplifier to the inverting input terminal of the operational amplifier to compensate the inverting input terminal of the operational amplifier; The filtering circuit is electrically connected to the non-inverting input terminal of the operational amplifier and the first reference voltage terminal, respectively, and is used to filter the first reference voltage at the first reference voltage terminal to form a bias voltage and introduce it into the non-inverting input terminal of the operational amplifier, and use the bias voltage as the output voltage of the output terminal of the operational amplifier when no electrical signal input by the piezoelectric sensor is received; The reset circuit is electrically connected to the processing unit and the operational amplifier, respectively, and is configured to restore the output voltage of the output end of the operational amplifier to the bias voltage when receiving a reset signal output from the processing unit.

3. The piezoelectric ceramic static force detection device according to claim 2, characterized in that: The feedback circuit includes a first resistor and a first capacitor, wherein the first end of the first resistor and the first end of the first capacitor are electrically connected to the inverting input terminal of the operational amplifier, and the second end of the first resistor and the second end of the first capacitor are electrically connected to the output terminal of the operational amplifier.

4. The piezoelectric ceramic static force detection device according to claim 2, characterized in that: The filtering circuit includes a second resistor and a second capacitor, wherein the first end of the second resistor and the first end of the second capacitor are electrically connected to the non-inverting input terminal of the operational amplifier, and the second end of the second resistor and the second end of the second capacitor are electrically connected to the first reference voltage terminal.

5. The piezoelectric ceramic static force detection device according to claim 3, characterized in that: The reset circuit includes a first transistor and a second transistor; wherein: The base of the first transistor receives a reset signal applied by the processing unit, the emitter of the first transistor is electrically connected to the first end of the first resistor, the first end of the first capacitor, and the inverting input terminal of the operational amplifier, respectively, and the collector of the first transistor is electrically connected to the second end of the first resistor, the second end of the first capacitor, and the output terminal of the operational amplifier, respectively; The base of the second transistor receives a reset signal applied from the processing unit, the emitter of the second transistor is electrically connected to the first end of the second resistor, the first end of the second capacitor and the non-inverting input terminal of the operational amplifier, and the collector of the second transistor is electrically connected to the second end of the second resistor, the second end of the second capacitor and the first reference voltage terminal.

6. The piezoelectric ceramic static force detection device according to claim 3, characterized in that: The reset circuit includes a third MOS transistor, a fifth resistor, a fourth MOS transistor and a sixth resistor; wherein: The gate of the third MOS transistor receives the first reset signal applied by the processing unit, the source of the third MOS transistor is grounded, and the drain of the third MOS transistor is electrically connected to the first end of the first resistor, the first end of the first capacitor, and the inverting input terminal of the operational amplifier through the fifth resistor. The gate of the fourth MOS transistor receives the second reset signal applied by the processing unit, the drain of the fourth MOS transistor is electrically connected to the first end of the second resistor, the first end of the second capacitor, and the non-inverting input terminal of the operational amplifier through the sixth resistor, and the source of the fourth MOS transistor is electrically connected to the second reference voltage terminal.

7. The piezoelectric ceramic static force detection device according to claim 5, characterized in that: The charge amplifier also includes a first low-pass filter, which is electrically connected to the inverting input terminal of the operational amplifier and the piezoelectric sensor, respectively, and is used to low-pass filter the electrical signal of the piezoelectric sensor input to the inverting input terminal of the operational amplifier.

8. The piezoelectric ceramic static force detection device according to claim 7, characterized in that: The first low-pass filter includes a third resistor and a third capacitor, the first end of the third resistor is electrically connected to the piezoelectric sensor, the second end of the third resistor is electrically connected to the first end of the third capacitor and then electrically connected to the inverting input terminal of the operational amplifier, and the second end of the third capacitor is grounded.

9. The piezoelectric ceramic static force detection device according to claim 5, characterized in that: The charge amplifier also includes a second low-pass filter, which is electrically connected to the non-inverting input terminal of the operational amplifier and the piezoelectric sensor, respectively, and is used to low-pass filter the electrical signal of the piezoelectric sensor input to the non-inverting input terminal of the operational amplifier.

10. The piezoelectric ceramic static force detection device according to claim 9, characterized in that: The second low-pass filter includes a fourth resistor and a fourth capacitor, the first end of the fourth resistor is electrically connected to the piezoelectric sensor, the second end of the fourth resistor is electrically connected to the first end of the fourth capacitor and then electrically connected to the non-inverting input terminal of the operational amplifier, and the second end of the fourth capacitor is grounded.

11. The piezoelectric ceramic static force detection device according to claim 1, characterized in that: The processing unit is also used to compensate the output voltage of the charge amplifier; specifically: determine whether the output voltage of the charge amplifier is greater than a trigger threshold; if so, further determine whether the difference between the current time constant and the time constant at the previous moment is less than a time constant error threshold; if the difference is less than the time constant error threshold, compensate the output voltage of the charge amplifier; if the difference is greater than or equal to the time constant error threshold, abandon compensating the output voltage of the charge amplifier.

12. An electronic device, characterized in that: The electronic device comprises the piezoelectric ceramic static force detection device according to any one of claims 1 to 11.

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