Ultrasonic signal receiving circuit and signal detection method

Abstract

The present invention provides an ultrasonic signal receiving circuit, a piezoelectric element, which is configured to receive an ultrasonic signal and convert it into a corresponding charge signal; a peak detection circuit, which is used to detect the charge signal output by the piezoelectric element; an amplifier circuit, which is connected to the peak detection circuit and is used to amplify the charge signal to generate an output signal; the peak detection circuit includes a first reference voltage that is turned on during peak detection; this solution has the characteristics of low power consumption and simple design.

Description

Technical Field

[0001] The invention belongs to the field of TFT ultrasonic sensors, and in particular relates to an improvement on a signal receiving circuit of an ultrasonic image sensor. Background Art

[0002] Fingerprint recognition is the most widely used biometric technology. In recent years, fingerprint collection technologies based on heat, electricity, sound, light and other methods have been developed. Since 2013, Apple has used capacitive fingerprint sensors on its mobile phone products, and fingerprint recognition sensors have been widely used on mobile phones. However, the penetration ability of capacitive fingerprint sensors on surface materials is less than 400um, which cannot support the requirements of fingerprint recognition under the screen. At present, the development trend of mobile phones is full screen, and the fingerprint recognition sensor on the front needs to have a penetration of more than 1mm to penetrate the screen. There are two main fingerprint recognition technologies that can achieve a penetration of more than 1mm: optical collection technology and ultrasonic collection technology. Especially ultrasonic technology, the module is thinner, the collection area is larger, and compared with optics, it is not affected by the external environment. Ultrasonic technology will become the mainstream fingerprint collection technology for subsequent mobile devices.

[0003] Qualcomm has successfully used ultrasonic fingerprint recognition technology on mobile phones. Its third-generation product is expected to penetrate a screen of about 1.5mm to match the structural design of full-screen mobile phones. The solution includes a global drive signal DBIAS, which is connected to each pixel. When the sensor switches from waiting mode to acquisition mode, DBIAS must change from level signal 1 to level signal 2, and when the sensor switches from acquisition mode to waiting mode, DBIAS must change from level signal 2 to level signal 1; due to the presence of parasitic resistance and parasitic capacitance of the routing, the DBIAS received by each pixel will have a large delay, resulting in a large inconsistency in the image collected by the sensor; in addition, because DBIAS is a global driver, it requires a large driving capability and driving speed. The driver buffer at the front end of DBIAS must have a large driving capability and a fast enough driving speed, which will also consume a lot of power. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an ultrasonic signal receiving circuit, comprising:

[0005] a piezoelectric element configured to receive an ultrasonic signal and convert it into a corresponding charge signal;

[0006] A peak detection circuit, used for detecting the charge signal output by the piezoelectric element;

[0007] an amplifier circuit, connected to the peak detection circuit, and used to amplify the charge signal to generate an output signal;

[0008] The peak detection circuit includes a first reference voltage that is turned on during peak detection.

[0009] Preferably, the peak detection circuit includes a diode having a first pole connected to the piezoelectric element, and a second pole of the diode connected to the first reference voltage via a switch; and further includes a second switch connecting the first pole of the diode and a second reference voltage.

[0010] Preferably, the input end of the amplifier circuit is connected to the first electrode of the diode, and the output end of the amplifier circuit is connected to the output switch.

[0011] Preferably, the amplifier circuit comprises a first thin film transistor, a gate of the first thin film transistor is connected to the first electrode of the diode, a source of the first thin film transistor is connected to the output switch, and a drain of the first thin film transistor is connected to the power supply terminal.

[0012] Preferably, the output switch is a second thin film transistor, and a source of the second thin film transistor is connected to a source of the first thin film transistor.

[0013] Preferably, the piezoelectric unit comprises a piezoelectric material and electrodes arranged at both ends of the piezoelectric material and one side of the piezoelectric material is a charge output electrode, and the second switch is connected to the charge output electrode.

[0014] Preferably, the first switch is closed upon peak detection.

[0015] Preferably, the amplification circuit converts the charge signal into a current signal.

[0016] Another invention of the present invention provides a method for receiving an ultrasonic signal, comprising the steps of:

[0017] The piezoelectric unit transmits an ultrasonic signal;

[0018] The piezoelectric element receives the ultrasonic signal and converts it into a corresponding charge signal;

[0019] A peak detection circuit receives and accumulates the charge signal;

[0020] The output switch is turned on, and the amplifier circuit outputs a current signal related to the charge signal.

[0021] Preferably, the step of "the piezoelectric unit emitting an ultrasonic signal" includes: closing the second switch; and inputting a driving signal to the piezoelectric unit.

[0022] Preferably, the step of "the peak detection circuit receives and accumulates the charge signal" includes: closing the first switch so that the second electrode of the diode is connected to the first reference voltage.

[0023] Preferably, the step of “closing the second switch to reset the peak detection circuit” includes: closing the second switch so that the first electrode of the diode is connected to the second reference voltage.

[0024] The beneficial technical effect of the present invention compared with the prior art is that a new first reference voltage is used to replace the global driving signal, a new TFT circuit method is proposed, and the use of a global driving signal is avoided. A switch and a reference voltage VREF are used to control the diode, which reduces the design difficulty of the driver and reduces the power consumption, and can also improve the consistency of the output signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of the ultrasonic receiving circuit module of the present invention.

[0026] Figure 2 This is a schematic diagram of the structure of the ultrasonic receiving circuit of the present invention.

[0027] Figure 3 This is a schematic diagram of the working timing of the ultrasonic receiving circuit of the present invention. DETAILED DESCRIPTION

[0028] Reference Figures 1 to 3 The ultrasonic signal receiving circuit 100 shown in the figure uses a first reference voltage Vref1 to replace the global drive during peak detection. The ultrasonic signal receiving circuit includes a piezoelectric element 11 configured to receive an ultrasonic signal and convert it into a corresponding charge signal; a peak detection circuit 12 for detecting the charge signal output by the piezoelectric element 11; an amplifier circuit 13 connected to the peak detection circuit 12 for amplifying the charge signal to generate an output signal; the peak detection circuit 12 includes a first reference voltage Vref1 that is turned on during peak detection.

[0029] The input end of the piezoelectric unit 11 is an ultrasonic signal u, and the intensity of the ultrasonic signal reflects the distance of the material reflecting the ultrasonic signal from the ultrasonic emission source. The piezoelectric unit 11 converts the ultrasonic signal into a charge signal, and generates a voltage signal Vin and a current signal corresponding to the charge signal. The voltage signal Vin and the current signal have substantially the same frequency as the signal emitted by the ultrasonic wave.

[0030] The piezoelectric element 11 shown includes a piezoelectric material layer 110 and electrodes 111 and 112 arranged on both sides thereof. The piezoelectric material layer 110 may include piezoelectric ceramics or piezoelectric polymers (PVDF), etc. The charge generated by the piezoelectric material layer 110 is output to the peak detection circuit 12 through the electrode 112. In a preferred embodiment, the piezoelectric unit 11 is used as a medium for transmitting and receiving ultrasonic signals at the same time. When transmitting, the piezoelectric unit is connected to the ultrasonic drive level DRV.

[0031] The input end 121 of the peak detection circuit 12 is connected to the output end 113 of the piezoelectric unit, and the peak detection circuit 12 is used to accumulate the charge signal and output the charge signal to the amplifier circuit 13. Peak detection refers to detecting the peak value or trough peak value of the voltage signal Vin corresponding to the ultrasonic signal.

[0032] The input end 131 of the amplifier circuit is connected to the output end of the peak detection circuit 122, and the output end of the amplifier circuit is connected to the output end out of the ultrasonic receiving circuit 100. The output signal can be a voltage signal or a current signal. The output current signal will be used as an example for explanation in this article.

[0033] Since the reference voltage Vref1 is a fixed value, the driving circuit of the peak detection circuit is simplified, and the power consumption of the driving circuit can be reduced by avoiding the use of a voltage variable driving circuit, while improving the consistency of the output signal.

[0034] The peak detection circuit includes a first pole D1 connected to a diode D of the piezoelectric element 11, and a connection node Rx between the peak detection circuit 12 and the piezoelectric element also serves as an output terminal 122 of the peak detection circuit 12; the node Rx of the peak detection circuit 12 is equivalent to a charge output node.

[0035] The second pole D2 of the diode D is connected to the first reference voltage Vref1 through the switch S1, and the first reference voltage Vref1 is used as the reference voltage for peak detection. The peak detection circuit 12 also includes a second switch S2 that connects the first pole D1 of the diode D and the second reference voltage. The second switch S2 is connected to the node Rx and the reference voltage Vref2, and the second switch S2 is used to reset the peak detection circuit 12, and the second reference voltage Vref2 is used to reset the charge at the node Rx. When the second switch S2 is closed, the node Rx is connected to the reference voltage Vref2, and the charge at the Rx node is reset to prevent cumulative errors caused by repeated detection.

[0036] During peak detection, the piezoelectric unit 11 outputs a voltage signal Vin corresponding to the ultrasonic signal. When the first switch S1 and the second switch S2 are disconnected, the voltage signal has approximately the same frequency as the ultrasonic signal. When the switch S1 is closed and the switch S2 is disconnected, when the voltage at the node Rx is at the trough of Vin, the voltage difference between the first pole D1 and the second pole D2 of the diode is greater than the conduction voltage of the diode, and the node Rx is charged and accumulates charge. It should be noted that when the diode is turned on, the waveform of the voltage signal Vin charged at the node RX is affected and the amplitude gradually decays. Ideally, the charge node Rx is charged immediately after half of the waveform cycle of the voltage signal V, but in reality, it may take multiple waveform cycles to complete the charging, and the charging process only lasts in the cycle where the voltage signal Vin is at the trough.

[0037] The amplifier circuit 13 is connected to the node Rx, the charge of the node Rx is input to the amplifier circuit 13, and the amplifier circuit 13 forms a current signal i corresponding to the charge amount, and the intensity of the current signal is related to the gain value of the amplifier circuit and the charge amount of the node at Rx. The input end of the amplifier circuit 13 is connected to the first pole D1 of the diode D, and the output end of the amplifier circuit 13 is connected to the output switch T2.

[0038] like Figure 2 As shown, the amplifier circuit 13 includes a first thin film transistor T1, the gate of the first thin film transistor is connected to the node Rx, the drain T12 is connected to the power supply terminal Vcc, the charge at the node Rx can generate a voltage to turn on the first thin film transistor T1, and the larger the charge amount at the node Rx, the larger the current of the corresponding source T11.

[0039] The output switch is a second thin film transistor T2, and the source T21 of the second thin film transistor is connected to the source T11 of the first thin film transistor. The output switch T2 can be a row selection switch of an ultrasonic detection circuit array. The ultrasonic detection circuit can form an image sensor for detecting the surface image of an object in the form of an array, a single ultrasonic detection circuit serves as a pixel of the image sensor, and the output switch T2 serves as a row selection switch of a row or column of the ultrasonic detection circuit. For example, in an ultrasonic fingerprint sensor, the signal strength of the reflected wave of the ultrasonic wave is related to the ridge or valley line of the fingerprint surface. The signal strength of the ultrasonic wave reflected by the valley line is greater than the signal strength of the ultrasonic wave reflected by the ridge line. Therefore, the charge amount of the node Rx corresponding to the valley line reflection wave is greater than the charge amount of the node Rx corresponding to the ridge line. The ultrasonic detection circuit 100 outputs the corresponding single pixel value formed by the pixel signal according to the charge amount of the node Rx, and the pixel value output by the ultrasonic detection circuit array forms an ultrasonic image.

[0040] Reference Figure 3 Based on the above ultrasonic detection circuit, the present invention also provides a method for receiving ultrasonic signals, comprising the steps of:

[0041] The piezoelectric unit 11 emits an ultrasonic signal;

[0042] The piezoelectric element receives the ultrasonic signal and converts it into a corresponding charge signal;

[0043] The peak detection circuit 12 receives and accumulates the charge signal;

[0044] The output switch T2 is turned on, and the amplifier circuit 13 outputs a current signal i related to the charge signal.

[0045] When the piezoelectric unit 11 transmits an ultrasonic signal, the second switch S2 is closed, and the piezoelectric element 11 is connected to the driving level signal DRV. Before time t1, the control signals of the first switch S1, the second switch S2, and the output switch T2 are all kept in a low potential state, that is, all disconnected, and the DRV driving level remains in the initial state. At time t1, the second switch S2 is closed, the charge of the node Rx is reset, and the control signals of the first switch S1 and the output switch T2 are kept in a low level state and the two switches are disconnected. After a certain delay, the driving level DRV generates a driving signal ds, and the piezoelectric material 110 is stimulated by the driving signal ds to emit an ultrasonic signal with a frequency that is substantially the same as the frequency of the driving signal ds.

[0046] During the period from t3 to t4, the piezoelectric element receives the ultrasonic signal and converts it into a corresponding charge signal. Before the moment t2, the transmission of the ultrasonic signal is completed to complete a beam of ultrasonic pulse signals, and the second switch S2 is disconnected after a certain delay. During the period from t3 to t4, the first switch S1 closes the second pole D2 of the diode D and connects it to the first reference voltage Vref1. At the same time, the reflected wave of the ultrasonic pulse signal emitted during the period from t1 to t2 is received by the piezoelectric element 11, and the piezoelectric element 11 receives the ultrasonic signal and converts it into a corresponding charge signal, which has a corresponding voltage signal Vin. When the voltage signal Vin is a trough, the voltage difference on both sides of the diode D reaches the conduction voltage difference, and the charge accumulates at the node Rx through the diode D. During the stage from t3 to t4, the first and second switches S1 and S2 output switch T2 remain closed, and the drive signal DRV is in the initial state.

[0047] During the period from t5 to t6, the output switch T2 turns on the amplifier circuit 13 to output a current signal i related to the charge of the node Rx to the output port out. The output port i can be connected to a peripheral circuit, which may include an analog-to-digital conversion circuit (ADC) and an image processor connected to the analog-to-digital conversion circuit.

Claims

1. An ultrasonic signal receiving circuit, Features include: a piezoelectric element configured to receive an ultrasonic signal and convert it into a corresponding charge signal; A peak detection circuit, used for detecting the charge signal output by the piezoelectric element; an amplifier circuit, connected to the peak detection circuit, and configured to amplify the charge signal to generate an output signal; The peak detection circuit includes a diode, a first switch, a first reference voltage, and a second reference voltage; The first electrode of the diode is connected to the piezoelectric element; The input end of the amplifier circuit is connected to the first electrode of the diode; The second electrode of the diode is connected to the first reference voltage through the first switch; The first switch is closed during peak detection; The peak detection circuit also includes a second switch connected to the first electrode of the diode and a second reference voltage; The peak detection circuit is reset when the second switch is closed.

2. The ultrasonic signal receiving circuit according to claim 1, It is characterized in that The piezoelectric unit includes a piezoelectric material and electrodes arranged at two ends of the piezoelectric material, one end of which is a charge output electrode and the other end is a driving electrode. The first electrode of the diode is connected to the charge output electrode.

3. The ultrasonic signal receiving circuit according to claim 1, It is characterized in that The amplifier circuit converts the charge signal into a current signal.

4. The ultrasonic signal receiving circuit according to claim 3, It is characterized in that The amplifier circuit includes a first thin film transistor, a gate of the first thin film transistor is connected to the first electrode of the diode, a source of the first thin film transistor is connected to the output switch, and a drain of the first thin film transistor is connected to the power supply end.

5. The ultrasonic signal receiving circuit according to claim 4, It is characterized in that The output end of the amplifier circuit is connected to the output switch.

6. The ultrasonic signal receiving circuit according to claim 5, It is characterized in that The output switch is a second thin film transistor, and a source of the second thin film transistor is connected to a source of the first thin film transistor.

7. A method for detecting an ultrasonic signal, using the ultrasonic signal receiving circuit as claimed in any one of claims 1 to 6, Features Includes steps: closing the second switch; The piezoelectric unit transmits an ultrasonic signal; The piezoelectric element receives the ultrasonic signal and converts it into a corresponding charge signal; A peak detection circuit receives and accumulates the charge signal; The output switch is turned on, and the amplifier circuit outputs a current signal related to the charge signal.

8. The method for detecting an ultrasonic signal according to claim 7, It is characterized in that The step of "the piezoelectric unit transmits an ultrasonic signal" includes: inputting a driving signal to the piezoelectric unit.

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