Ultrasonic fingerprint recognition circuit and driving method, fingerprint recognition unit, and display device

Abstract

The present disclosure provides an ultrasonic fingerprint recognition circuit and a driving method thereof, a fingerprint recognition unit, and a display device. The ultrasonic fingerprint recognition circuit includes: an ultrasonic sensor, configured to generate a first ultrasonic signal for fingerprint detection based on an input signal, and to generate an AC echo signal based on the echo signal after fingerprint detection; a signal conversion unit, one end of which is connected to the ultrasonic sensor, configured to receive the AC echo signal and convert the AC echo signal into a DC signal; a signal output unit, connected to the other end of the signal conversion unit, configured to receive the DC signal and generate a fingerprint recognition signal based on the DC signal. The ultrasonic fingerprint recognition circuit and a driving method thereof, the fingerprint recognition unit, and the display device disclosed in the present disclosure can recognize the echo signal after fingerprint detection without providing a bootstrap voltage, thereby reducing the process difficulty.

Description

Technical Field

[0001] The present disclosure relates to the field of fingerprint recognition technology, and in particular to an ultrasonic fingerprint recognition circuit and a driving method thereof, a fingerprint recognition unit, and a display device. Background Art

[0002] Fingerprint recognition technology can authenticate users through fingerprints, thereby improving the security of display devices. Among them, ultrasonic fingerprint recognition technology, as an emerging fingerprint recognition technology, has gradually attracted people's attention. Since ultrasound has strong penetrability, it can also recognize fingerprints when there are water stains and stains on the surface of the finger, so the application of ultrasonic fingerprint recognition technology is becoming more and more widespread.

[0003] However, the current integrated solution for ultrasonic fingerprint recognition uses a filtered integral signal method. Since the filtered signal is relatively weak, the collected current signal may be too small, resulting in false alarms. This will require requirements for the resistance of the circuit routing, increasing the difficulty of the process. Summary of the invention

[0004] In view of this, the purpose of the present disclosure is to provide an ultrasonic fingerprint recognition circuit and a driving method thereof, a fingerprint recognition unit, and a display device.

[0005] Based on the above objectives, the present disclosure provides an ultrasonic fingerprint recognition circuit, comprising:

[0006] An ultrasonic sensor configured to generate a first ultrasonic signal for fingerprint detection based on an input signal, and to generate an AC echo signal based on an echo signal after fingerprint detection;

[0007] A signal conversion unit, one end of which is connected to the ultrasonic sensor and configured to receive the AC echo signal and convert the AC echo signal into a DC signal;

[0008] The signal output unit is connected to the other end of the signal conversion unit and is configured to receive the DC signal and generate a fingerprint recognition signal based on the DC signal.

[0009] Optionally, the ultrasonic sensor includes a transmitting electrode, a receiving electrode, and a piezoelectric layer arranged between the transmitting electrode and the receiving electrode;

[0010] The transmitting electrode is configured to receive the input signal and input a first voltage to the piezoelectric layer based on the input signal; the input signal is an AC signal;

[0011] The piezoelectric layer is configured to transmit the first ultrasonic signal in response to the first voltage, and to generate the AC echo signal in response to the echo signal reflected by the fingerprint and output it to the signal conversion unit through the receiving electrode.

[0012] Optionally, the signal conversion unit includes an inverter and a first voltage signal terminal and a second voltage signal terminal connected to the inverter;

[0013] The inverter is configured to generate the DC signal based on the AC echo signal, the first voltage signal input to the first voltage signal terminal, and the second voltage signal input to the second voltage signal terminal.

[0014] Optionally, the inverter includes a first field effect transistor and a second field effect transistor;

[0015] The control electrode of the first field effect transistor is connected to the ultrasonic sensor, the first electrode of the first field effect transistor is connected to the first voltage signal terminal, and the second electrode of the first field effect transistor is connected to the signal output unit;

[0016] The control electrode of the second field effect tube is connected to the ultrasonic sensor, the first electrode of the second field effect tube is connected to the second voltage signal end, and the second electrode of the second field effect tube is connected to the signal output unit.

[0017] Optionally, one of the first field effect transistor and the second field effect transistor is a P-type field effect transistor, and the other is an N-type field effect transistor.

[0018] Optionally, the first electrode of the first field effect transistor and the first electrode of the second field effect transistor are sources, and the second electrode of the first field effect transistor and the second electrode of the second field effect transistor are drains.

[0019] Optionally, the signal output unit includes a first thin film transistor and a second thin film transistor;

[0020] The control electrode of the first thin film transistor is connected to the second electrode of the first field effect transistor and the second electrode of the second field effect transistor respectively, the first electrode of the first thin film transistor is connected to the third voltage signal terminal, and the second electrode of the first thin film transistor is connected to the first electrode of the second thin film transistor;

[0021] The control electrode of the second thin film transistor is connected to the fourth voltage signal terminal, and the second electrode of the second thin film transistor is connected to the signal output terminal of the signal output unit.

[0022] The present disclosure also provides a fingerprint recognition unit, comprising at least one ultrasonic fingerprint recognition circuit as described in any one of the above embodiments.

[0023] The present disclosure further provides a display device, comprising a display module and a fingerprint recognition unit as described in the above embodiment, wherein the fingerprint recognition unit is attached to a light emitting surface or a backlight surface of the display module.

[0024] Optionally, the fingerprint recognition unit includes a stacked fingerprint recognition backplane and an ultrasonic sensor film layer, the fingerprint recognition backplane is arranged on one side of the display module, and the ultrasonic sensor film layer is arranged on a side of the fingerprint recognition backplane away from the display module or between the fingerprint recognition backplane and the display module.

[0025] Optionally, the display module includes a display substrate, a pixel driving circuit unit and a light-emitting unit which are stacked in sequence, the light-emitting unit includes an anode layer, a light-emitting layer and a cathode layer which are stacked in sequence away from the pixel driving circuit unit, and the fingerprint recognition unit includes a fingerprint recognition backplane and an ultrasonic sensor film layer arranged between the display substrate and the cathode layer.

[0026] Optionally, the fingerprint recognition backplane includes a signal conversion unit and a signal output unit, and the ultrasonic sensor film layer includes a transmitting electrode arranged on one side of the fingerprint recognition backplane, a receiving electrode arranged between the fingerprint recognition backplane and the transmitting electrode, and a piezoelectric layer arranged between the transmitting electrode and the receiving electrode.

[0027] Optionally, the transmitting electrode and the receiving electrode are arranged in a one-to-one correspondence, and the orthographic projection of the transmitting electrode on the display substrate coincides with the orthographic projection of the receiving electrode on the display substrate.

[0028] The present disclosure also provides a driving method of an ultrasonic fingerprint recognition circuit, comprising:

[0029] In the transmitting stage, the ultrasonic sensor receives an input signal to generate a first ultrasonic signal for fingerprint detection;

[0030] In the receiving stage, the ultrasonic sensor receives the echo signal after fingerprint detection to generate an AC echo signal and sends it to the signal conversion unit; the signal conversion unit converts the AC echo signal into a DC signal and sends it to the signal output unit; the signal output unit generates a fingerprint recognition signal based on the DC signal.

[0031] It can be seen from the above that the ultrasonic fingerprint recognition circuit and its driving method, fingerprint recognition unit, and display device provided by the present disclosure generate a first ultrasonic signal for detecting fingerprints through an ultrasonic sensor, and generate an AC echo signal based on the echo signal after fingerprint detection; the AC echo signal is converted into a DC signal through a signal conversion unit and output to a signal output unit, so that the signal output unit can generate a fingerprint recognition signal for fingerprint recognition; the signal conversion unit can convert both positive voltage signals and negative voltage signals, so when the AC echo signal is converted into a DC signal, no additional boosting voltage is required to convert both the positive and negative voltages in the AC echo signal, so that even if the Dbias signal with a bootstrap voltage is not provided, the negative voltage part in the AC echo signal will not be lost, thereby reducing the problem of increased process difficulty caused by designing the Dbias part and reducing the process difficulty in the circuit manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present disclosure or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 It is a circuit structure schematic diagram of an ultrasonic fingerprint recognition circuit in the prior art;

[0034] Figure 2 It is a schematic diagram of the working timing of the ultrasonic fingerprint recognition circuit in the prior art;

[0035] Figure 3 is a structural block diagram of an ultrasonic fingerprint recognition circuit according to an embodiment of the present disclosure;

[0036] Figure 4 is another structural block diagram of the ultrasonic fingerprint recognition circuit according to an embodiment of the present disclosure;

[0037] Figure 5 Schematic diagram of the circuit structure of the ultrasonic fingerprint recognition circuit of the embodiment of the present disclosure;

[0038] Figure 6 Schematic diagram of input and output voltage curves of the inverter according to an embodiment of the present disclosure;

[0039] Figure 7 This is a schematic diagram of various voltage indicators of the inverter under different voltage conditions according to the embodiment of the present disclosure;

[0040] Figure 8a This is a schematic diagram of the structure of a display device in which a fingerprint recognition unit is arranged on the light-emitting side of a display module according to an embodiment of the present disclosure;

[0041] Figure 8b This is a schematic diagram of another display device structure in which the fingerprint recognition unit is arranged on the light-emitting side of the display module according to an embodiment of the present disclosure;

[0042] Figure 8c This is a schematic diagram of the structure of a display device in which a fingerprint recognition unit is arranged on the backlight side of a display module according to an embodiment of the present disclosure;

[0043] Figure 8d This is a schematic diagram of another display device structure in which the fingerprint recognition unit is disposed on the backlight side of the display module according to an embodiment of the present disclosure;

[0044] Figure 9a This is a schematic diagram of the structure of a display device in which a fingerprint recognition unit is disposed between a display substrate and a cathode layer according to an embodiment of the present disclosure;

[0045] Figure 9b This is a schematic diagram of another display device structure in which the fingerprint recognition unit is disposed between the display substrate and the cathode layer according to an embodiment of the present disclosure;

[0046] Fig.10a is a schematic diagram of a specific structure of a display device according to an embodiment of the present disclosure;

[0047] Fig.10b is another specific structural schematic diagram of the display device according to an embodiment of the present disclosure;

[0048] Fig.11 The figure is a flow chart of a driving method of an ultrasonic fingerprint recognition circuit according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0050] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The words "first", "second" and similar words used in the embodiments of the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. Fingerprint recognition refers to identification by comparing the detailed feature points of different fingerprints. Since each person's fingerprint is different, even the fingerprints between the ten fingers of the same person are obviously different, so fingerprints can be used for identity authentication. Its lifelong invariance, uniqueness and convenience have almost become synonymous with biometric identification. Fingerprints are unique features of the human body and are extremely difficult to crack. At the same time, fingerprint recognition scanning speed is very fast. When applied to mobile display devices such as mobile phones, this undoubtedly makes mobile phone unlocking, mobile payment, etc. safer, more convenient and faster.

[0051] Fingerprint recognition refers to the identification by comparing the detailed feature points of different fingerprints. Since each person's fingerprint is different, and the fingerprints of the same person's ten fingers are also obviously different, fingerprints can be used for identity verification. Its advantages such as lifelong invariance, uniqueness and convenience have almost become synonymous with biometric identification. Fingerprints are unique features of the human body and are extremely difficult to crack. At the same time, fingerprint recognition scans very quickly and is applied to mobile display devices such as mobile phones. This undoubtedly makes mobile phone unlocking and mobile payments safer, more convenient and faster.

[0052] Fingerprint recognition technology is currently the most mainstream biometric recognition method, and its application and popularity far exceeds other recognition methods, such as iris recognition, vein recognition, and face recognition. With the further development of industrial design, the requirements for technology are getting higher and higher, and traditional fingerprint unlocking technology cannot meet the more stringent process level requirements.

[0053] Figure 1 It is a circuit diagram of an ultrasonic fingerprint recognition circuit in the prior art. Figure 2 FIG. 1 is a timing diagram of the operation of an ultrasonic fingerprint recognition circuit in the prior art. Figure 1 , Figure 2As shown, in the transmission phase between t0-t1, the input voltage of the reset signal Vrst is high, the input signal of Dbias is low, the transistor T0 is turned on, the receiving electrode is biased to a fixed potential (0), the transmitting electrode receives the AC signal vtx, and the piezoelectric layer vibrates to emit ultrasonic waves outward; in the sampling phase between t1-t2, the input voltage of the reset signal rst is low, the input signal of Dbias is briefly pulled high, charging the receiving node N, the voltage is stored on the parasitic capacitor Cp, the piezoelectric layer receives the echo and outputs the ultrasonic echo signal to the receiving electrode, and the final potential is affected by the ultrasonic echo signal; in the holding phase between t2-t3, the input signal of Dbias is appropriately biased to minimize the leakage current of the transistor T0; in the readout phase between t3-t4, the Vread signal input at the gate of the transistor SEL is pulled high, the transistor SEL is turned on, and the potential of the receiving node N is converted into a voltage signal for fingerprint recognition through the switch tube SF and output to the outside.

[0054] In the above ultrasonic fingerprint recognition circuit, due to the characteristics of the piezoelectric layer material, when the input AC signal vtx is about 200V, the voltage after passing through the piezoelectric layer is only about 1V, and the signal loss is very large; since the ultrasonic echo signal is also an AC signal, it includes positive voltage and negative voltage, and the negative voltage cannot turn on the switch tube SF. In order to turn on the switch tube SF, a bootstrap voltage input by Dbias is required to lift the ultrasonic echo signal to a positive voltage signal, thereby successfully turning on the switch tube SF to output a voltage signal for fingerprint recognition. In this case, in order to ensure that the switch tube SF can be smoothly turned on and output a current signal for fingerprint recognition, the following requirements must be met: the Dbias signal that provides the bootstrap voltage must be a global signal with a high bandwidth (50ns square wave), requiring a small wiring delay and a complete waveform; AP must be a global signal, an array power supply must be provided, and a small resistance must be required; the reset signal Vrst is connected to the next row Vsel, and is led out every two rows, requiring a small resistance; the signal output terminal Dn requires each column to be led out, with the wiring as short as possible and low noise. This greatly increases the process complexity of ultrasonic fingerprint recognition circuit manufacturing and improves the process difficulty of circuit manufacturing.

[0055] In the process of implementing the present disclosure, the applicant discovered that if the AC signal of the ultrasonic echo signal can be directly processed, the ultrasonic echo signal can be converted from an AC signal to a DC signal without the bootstrap voltage provided by Dbias, and the switch tube SF can be turned on without losing the negative voltage signal in the AC signal, then the process burden can be reduced while ensuring the accuracy of the fingerprint recognition function.

[0056] The technical solution of the present disclosure is further described in detail below through specific embodiments.

[0057] Figure 3A block diagram of an ultrasonic fingerprint recognition circuit provided by one or more embodiments of the present disclosure. Figure 3 As shown, one or more embodiments of the present disclosure provide an ultrasonic fingerprint recognition circuit, which includes an ultrasonic sensor 1, a signal conversion unit 2 and a signal output unit 3.

[0058] The ultrasonic sensor 1 is configured to generate a first ultrasonic signal for fingerprint detection based on an input signal, and to generate an AC echo signal based on an echo signal after fingerprint detection. In this embodiment, the ultrasonic sensor 1 is connected to the signal input terminal 10, the signal input terminal 10 generates an input signal and inputs the input signal to the ultrasonic sensor 1, the ultrasonic sensor 1 receives the input signal, generates and transmits a first ultrasonic signal, after the first ultrasonic signal reaches the user's finger, the valley ridge part of the fingerprint reflects the first ultrasonic signal to generate an echo signal, the echo signal is absorbed by the ultrasonic sensor 1, and then generates an AC echo signal and sends it to the signal conversion unit 2.

[0059] One end of the signal conversion unit 2 is connected to the ultrasonic sensor 1, and the signal conversion unit 2 is configured to receive the AC echo signal and convert the AC echo signal into a DC signal. In this embodiment, the signal conversion unit 2 can convert positive voltage and negative voltage, so when the AC echo signal is converted into a DC signal, the negative voltage part of the AC echo signal will not be lost, so that compared with directly outputting the AC echo signal to the signal output unit 3, the echo signal can be amplified to a certain extent.

[0060] The signal output unit 3 is connected to the other end of the signal conversion unit 2, and the signal output unit 3 is configured to receive the DC signal, and generate a fingerprint recognition signal based on the DC signal and send it to the signal output terminal 30. In this embodiment, the signal output terminal 30 receives the fingerprint recognition signal output by the signal output unit 3, analyzes and processes the fingerprint recognition signal, thereby realizing the fingerprint recognition function.

[0061] In this embodiment, a first ultrasonic signal for detecting fingerprints is generated by an ultrasonic sensor 1, and an AC echo signal is generated based on the echo signal after fingerprint detection; the AC echo signal is converted into a DC signal by a signal conversion unit 2 and output to a signal output unit 3, so that the signal output unit 3 can generate a fingerprint recognition signal for fingerprint recognition; the signal conversion unit 2 can convert both positive voltage signals and negative voltage signals, so when converting the AC echo signal into a DC signal, no additional boosting voltage is required, and both positive and negative voltages in the AC echo signal can be converted, so that even if the Dbias signal with a bootstrap voltage is not provided, the negative voltage part in the AC echo signal will not be lost, thereby reducing the problem of increased process difficulty caused by designing the Dbias part and reducing the process difficulty in the circuit manufacturing process.

[0062] In some embodiments of the present disclosure, Figure 5 As shown, the ultrasonic sensor 1 includes a transmitting electrode 11, a receiving electrode 13, and a piezoelectric layer 12 disposed between the transmitting electrode 11 and the receiving electrode 13. The transmitting electrode 11 is configured to receive the input signal and input a first voltage to the piezoelectric layer 12 based on the input signal; the input signal is an AC signal. The piezoelectric layer 12 is configured to transmit the first ultrasonic signal in response to the first voltage, and to generate the AC echo signal in response to the echo signal reflected by the fingerprint through the receiving electrode 13 and output it to the signal conversion unit 2.

[0063] In specific applications, the transmitting electrode 11 can be configured to receive an AC signal during the transmitting phase, and input a first voltage to the piezoelectric layer 12 based on the AC signal. The AC signal can be input through the signal input terminal 10. During operation, there will be a residual voltage between the receiving electrode 13 and the signal conversion unit 2, so that a second voltage can be formed on the receiving electrode 13. In this way, the piezoelectric layer 13 can be configured to emit a first ultrasonic signal in response to the AC signal on the transmitting electrode 11 and the second voltage on the receiving electrode 13 during the transmitting phase. That is, based on the piezoelectric characteristics, the piezoelectric layer 12 can vibrate under the combined action of the AC signal on the transmitting electrode 11 and the second voltage on the receiving electrode 13, thereby generating a first ultrasonic signal and emitting it. Optionally, the material of the piezoelectric layer 12 may include at least one of PVDF (polyvinylidene fluoride), AlN (aluminum nitride), aluminum nitride (AlN), PZT (lead zirconate titanate), ZnO (zinc oxide), lithium niobate (LiNbO3), quartz (Quartz), potassium niobate (KNbO3) or lithium tantalate (LiTaO3); the material of the transmitting electrode 11 may be metal materials such as gold (Au), molybdenum (Mo), platinum (Pt), aluminum (Al), silver (Ag), titanium (Ti), etc.; the material of the receiving electrode 13 may be gold (Au), molybdenum (Mo), platinum (Pt), aluminum (Al), silver (Ag), titanium (Ti), ITO (indium tin oxide), etc., and the embodiment of the present invention does not specifically limit this.

[0064] Optionally, the receiving electrode 13 may be charged to form a second voltage on the receiving electrode 13 for generating the first ultrasonic signal.

[0065] When the first ultrasonic signal reaches the user's finger, the valley and ridge part of the fingerprint can reflect the first ultrasonic signal to form an echo signal. When the echo signal generated by the fingerprint reflection reaches the piezoelectric layer 12, the piezoelectric layer 12 can vibrate and generate a voltage change relative to the first voltage at the interface of the piezoelectric layer 12. Among them, the voltage change includes the valley signal generated by the valley in the fingerprint and the ridge signal generated by the ridge in the fingerprint. The valley signal or ridge signal generated by the piezoelectric layer 12 is received by the receiving electrode 13 to generate an AC echo signal, and then the receiving electrode 13 can transmit the AC echo signal to the signal conversion unit 2.

[0066] In some embodiments of the present disclosure, Figure 4 As shown, the signal conversion unit 2 includes an inverter 21 and a first voltage signal terminal 22 and a second voltage signal terminal 23 connected to the inverter 21. The inverter 21 is configured to generate the DC signal based on the AC echo signal, the first voltage signal input by the first voltage signal terminal 22, and the second voltage signal input by the second voltage signal terminal 23. In this embodiment, the inverter can convert both the positive voltage signal and the negative voltage signal into a positive voltage signal, and the inverter can play a filtering role. When the AC echo signal is converted into a DC signal, the positive and negative voltages in the AC echo signal can be converted without an additional boost voltage, so that the transistor in the signal output unit is turned on more completely, and the negative voltage part in the AC echo signal will not be lost even if the Dbias signal with a bootstrap voltage is not provided, thereby reducing the problem of increased process difficulty caused by the design of the Dbias part and reducing the process difficulty in the circuit manufacturing process.

[0067] At the same time, if Figure 6 As shown, in this embodiment, the transition region of the inverter is utilized, that is, when the AC echo signal is between the minimum input voltage VIL and the maximum input voltage VIH of the inverter, the output DC signal also has a certain amplification effect. In a specific embodiment, as Figure 7As shown, when the first voltage signal VDD is 4V, the minimum input voltage VIL=1.74V, and the maximum input voltage VIH=2.32V, the corresponding minimum output voltage VOL=0V and the maximum output voltage VOH=4V, that is, the change between the minimum input voltage VIL and the maximum input voltage VIH of the input AC echo signal is 0.58V, and the change of the DC signal output by the inverter 21 is 4V, so even if the AC echo signal returned by the ultrasonic sensor 1 is only about 1V, the DC voltage output after the inverter 21 is 4V, which is equivalent to an amplification effect. In this case, when the DC signal continues to input the signal output unit, due to the larger change of the DC signal, the control of the switch tube in the signal output unit 3 is more sensitive, so that the fingerprint recognition signal finally generated has a higher accuracy when performing fingerprint recognition.

[0068] Optionally, in the above embodiment, the amplification factor of the AC echo signal amplified by the transition zone of the inverter 21 is related to the slope of the transition zone of the inverter 21, and the DC signal output after amplification is related to the minimum output voltage VOL and the maximum output voltage VOH of the inverter 21. Therefore, the amplification factor can be adjusted by adjusting the transition zone curve of the inverter 21 through the process.

[0069] In some optional embodiments of the present disclosure, Figure 5 As shown, the inverter 21 includes a first field effect transistor 211 and a second field effect transistor 212. The control electrode of the first field effect transistor 211 is connected to the ultrasonic sensor 1, the first electrode of the first field effect transistor 211 is connected to the first voltage signal terminal 22, and the second electrode of the first field effect transistor 211 is connected to the signal output unit 3; the control electrode of the second field effect transistor 212 is connected to the ultrasonic sensor 1, the first electrode of the second field effect transistor 212 is connected to the second voltage signal terminal 23, and the second electrode of the second field effect transistor 212 is connected to the signal output unit 3.

[0070] Optionally, one of the first field effect transistor 211 and the second field effect transistor 212 is a P-type field effect transistor, and the other is an N-type field effect transistor. In a specific embodiment, the first field effect transistor 211 is a P-type field effect transistor, and the second field effect transistor 212 is an N-type field effect transistor. Since the N-type field effect transistor works under a positive gate voltage state and the P-type field effect transistor works under a negative gate voltage state, when the receiving electrode 13 outputs a positive voltage in the AC echo signal, the second field effect transistor 212 outputs a DC signal based on the AC echo signal and the second voltage signal; when the receiving electrode 13 outputs a negative voltage in the AC echo signal, the first field effect transistor 211 outputs a DC signal based on the AC echo signal and the second voltage signal. In this way, both the positive voltage signal and the negative voltage signal in the AC echo signal can be output without the need to provide an additional bootstrap voltage.

[0071] Optionally, the control electrode of the first field effect transistor 211 and the control electrode of the second field effect transistor 212 are gates, the first electrode of the first field effect transistor 211 and the first electrode of the second field effect transistor 212 are sources, and the second electrode of the first field effect transistor 211 and the second electrode of the second field effect transistor 212 are drains.

[0072] like Figure 5 As shown, the gate of the first field effect transistor 211 is connected to the receiving electrode 13 of the ultrasonic sensor 1, and the working state of the gate of the first field effect transistor 211 is controlled by the second voltage on the receiving electrode 13. The source of the first field effect transistor 211 is connected to the first voltage signal terminal 22, and is used to receive the first voltage signal input by the first voltage signal terminal 22; based on Figure 6 , Figure 7 It can be seen that the magnitude of the DC signal output by the inverter 21 is related to the first voltage signal, so the magnitude of the DC signal output by the inverter 21 can be affected by adjusting the magnitude of the first voltage signal input by the first voltage signal terminal 22. When making a circuit, the magnitude of the first voltage signal can be adjusted according to the circuit characteristics; after the adjustment, the first voltage signal terminal 22 inputs a stable first voltage signal. The drain of the first field effect transistor 211 is connected to the gate of the first thin film transistor 31 in the signal output unit 3.

[0073] like Figure 5 As shown, the gate of the second field effect transistor 212 is connected to the receiving electrode 13 of the ultrasonic sensor 1, and the working state of the gate of the second field effect transistor 212 is controlled by the second voltage on the receiving electrode 13. The source of the second field effect transistor 212 is connected to the second voltage signal terminal 23, and is used to receive the second voltage signal input by the second voltage signal terminal 23; based on Figure 6 , Figure 7It can be seen that the magnitude of the DC signal output by the inverter 21 is also related to the second voltage signal. Therefore, the magnitude of the DC signal output by the inverter 21 can be affected by adjusting the magnitude of the second voltage signal input by the second voltage signal terminal 23. When making the circuit, the magnitude of the second voltage signal can be adjusted according to the circuit characteristics. After the adjustment is completed, a stable second voltage signal is input to the second voltage signal terminal 23. The drain of the second field effect transistor 212 is connected to the gate of the first thin film transistor 31 in the signal output unit 3.

[0074] like Figure 7 As shown, taking the first voltage signal as an example, when the first voltage signal is 4V, the minimum input voltage VIL of the inverter 21 is 2.42V, the maximum input voltage VIH is 3.58V, and the corresponding minimum output voltage VOL is 0V and the maximum output voltage VOH is 4V; when the first voltage signal is 6V, the minimum input voltage VIL of the inverter 21 is 1.74V, the maximum input voltage VIH is 2.32V, and the corresponding minimum output voltage VOL is 0V and the maximum output voltage V OH=6V; when the first voltage signal is 8V, the minimum input voltage VIL=3.08V and the maximum input voltage VIH=4.82V of the inverter 21, the corresponding minimum output voltage VOL=0V and the maximum output voltage VOH=8V; when the first voltage signal is 10V, the minimum input voltage VIL=3.70V and the maximum input voltage VIH=6.10V of the inverter 21, the corresponding minimum output voltage VOL=0V and the maximum output voltage VOH=10V. It can be seen that the magnitude of the DC voltage output after the inverter 21 is also related to the magnitude of the first voltage signal. Similarly, the magnitude of the DC voltage output after the inverter 21 is also related to the magnitude of the second voltage signal. Therefore, the magnitude of the DC voltage output by the inverter can be further adjusted according to the magnitude of the first voltage signal and the second voltage signal, so as to better control the opening of the first thin film transistor 31 in the signal output unit 3.

[0075] Optionally, in the above embodiment, when the threshold voltages Vth of the first field effect transistor 211 and the second field effect transistor 212 in the inverter 21 are relatively symmetrical parameters, it is more conducive to the output of the voltage of the inverter 21 .

[0076] In some other optional embodiments of the present disclosure, Figure 5As shown, the signal output unit 3 includes a first thin film transistor 31 and a second thin film transistor 32. The control electrode of the first thin film transistor 31 is connected to the second electrode of the first field effect transistor 211 and the second electrode of the second field effect transistor 212 respectively, the first electrode of the first thin film transistor 31 is connected to the third voltage signal terminal 33, and the second electrode of the first thin film transistor 31 is connected to the first electrode of the second thin film transistor 32; the control electrode of the second thin film transistor 32 is connected to the fourth voltage signal terminal 34, and the second electrode of the second thin film transistor 32 is connected to the signal output terminal 30 of the signal output unit 3. Among them, the control electrode of the first thin film transistor 31 and the control electrode of the second thin film transistor 32 are gate electrodes, the first electrode of the first thin film transistor 31 and the first electrode of the second thin film transistor 32 are source electrodes or drain electrodes, and the second electrode of the first thin film transistor 31 and the second electrode of the second thin film transistor 32 are drain electrodes or source electrodes respectively.

[0077] In this embodiment, the gate of the first thin film transistor 31 is respectively connected to the drain of the first field effect transistor 211 and the drain of the second field effect transistor 212, and the first thin film transistor 31 is turned on by a DC signal output by at least one of the drain of the first field effect transistor 211 and the drain of the second field effect transistor 212; at the same time, the third voltage signal terminal 33 inputs a third voltage signal, and at the same time, the fourth voltage signal terminal 34 connected to the gate of the second thin film transistor 32 inputs a fourth voltage signal to control the turning on of the second thin film transistor 32. In this way, under the control of the DC signal, the fingerprint recognition signal is generated and output to the signal output terminal 30 together with the DC signal and the third voltage signal.

[0078] Based on the same inventive concept, corresponding to the ultrasonic fingerprint recognition circuit described in any of the above embodiments, one or more embodiments of the present disclosure further provide a fingerprint recognition unit, which includes at least one ultrasonic fingerprint recognition circuit as described in any of the above embodiments.

[0079] The fingerprint recognition unit of the above embodiment includes the corresponding ultrasonic fingerprint recognition circuit in any of the above embodiments, and has the beneficial effects of the corresponding ultrasonic fingerprint recognition circuit embodiment, which will not be described in detail here.

[0080] Based on the same inventive concept, corresponding to the fingerprint recognition unit described in any of the above embodiments, one or more embodiments of the present disclosure further provide a display device. Figures 8a-8d As shown, the display device includes a display module 5 and a fingerprint recognition unit as described in any of the above embodiments. Figure 8a , 8b As shown, the fingerprint recognition unit is attached to the light-emitting surface of the display module 5; or Figure 8c , 8dAs shown, the fingerprint recognition device 100 is attached to the backlight surface of the display module 5 .

[0081] like Figures 8a-8d As shown, the fingerprint recognition unit 100 includes a stacked fingerprint recognition back plate 4 and an ultrasonic sensor film layer 6, wherein the ultrasonic sensor film layer 6 is provided with various structures in the ultrasonic sensor 1. The fingerprint recognition back plate 4 is provided on one side of the display module 5, and the ultrasonic sensor film layer 6 is provided on a side of the fingerprint recognition back plate 4 away from the display module 5 or between the fingerprint recognition back plate 4 and the display module 5.

[0082] In some specific embodiments, Figure 8a As shown, the fingerprint recognition back plate 4 is arranged on the light emitting surface of the display module 5, and the ultrasonic sensor film layer 6 is arranged on the side of the fingerprint recognition back plate 4 away from the display module 5; Figure 8b As shown, the fingerprint recognition back plate 4 is arranged on the light-emitting surface of the display module 5, and the ultrasonic sensor film layer 6 is arranged between the fingerprint recognition back plate 4 and the display module 5; Figure 8c As shown, the fingerprint recognition back plate 4 is arranged on the backlight surface of the display module 5, and the ultrasonic sensor film layer 6 is arranged on the side of the fingerprint recognition back plate 4 away from the display module 5; Figure 8d As shown, the fingerprint recognition back plate 4 is arranged on the backlight surface of the display module 5 , and the ultrasonic sensor film layer 6 is arranged between the fingerprint recognition back plate 4 and the display module 5 .

[0083] In some optional embodiments, the display module 5 includes a display substrate 51, a pixel driving circuit unit and a light emitting unit stacked in sequence, and the light emitting unit includes an anode layer, a light emitting layer and a cathode layer 59 stacked in sequence away from the pixel driving circuit unit. Figure 9a , 9b As shown, the fingerprint recognition unit 11 is disposed between the display substrate 51 and the cathode layer 59. The fingerprint recognition unit 11 includes a stacked fingerprint recognition back plate 4 and an ultrasonic sensor film layer 6, and the fingerprint recognition back plate 4 and the ultrasonic sensor film layer 6 are both disposed between the display substrate 51 and the cathode layer 59. Figure 9a As shown, the ultrasonic sensor film layer 6 is disposed between the display substrate 51 and the fingerprint identification back plate 4; Figure 9b As shown, the ultrasonic sensor film layer 6 is arranged between the cathode layer 59 and the fingerprint identification back plate 4.

[0084] In this embodiment, the fingerprint recognition backplane 4 includes various structures in the signal conversion unit 2 and the signal output unit 3. The first field effect transistor 211 and the second field effect transistor 212 in the signal conversion unit 2 and the signal output unit 3 including the first thin film transistor 31, the second thin film transistor 32 and other structures are all made in the fingerprint recognition backplane 4, so that the various structures in the signal conversion unit 2 and the signal output unit 3 can be made at the same time, thereby reducing the process steps.

[0085] Optionally, the ultrasonic sensor film layer 6 includes a transmitting electrode 11 disposed on one side of the fingerprint recognition back plate 4, a receiving electrode 13 disposed between the fingerprint recognition back plate 4 and the transmitting electrode 11, and a piezoelectric layer 12 disposed between the transmitting electrode 11 and the receiving electrode 13. The transmitting electrode 11 and the receiving electrode 13 are disposed in a one-to-one correspondence, and the orthographic projection of the transmitting electrode 11 on the display module 5 or the display substrate 51 coincides with the orthographic projection of the receiving electrode 13 on the display module 5 or the display substrate 51, so that the first ultrasonic signal can be emitted and an AC echo signal can be generated based on the echo signal received by the piezoelectric layer 12.

[0086] Optionally, in the above embodiment, when the transmitting electrode 11, the receiving electrode 13 and other structures are made of non-light-transmitting materials and the fingerprint recognition unit 100 is attached to the light-emitting surface of the display module 5, it is necessary to ensure that the non-light-transmitting structure of the fingerprint recognition unit 100 will not block the light-emitting unit of the display module 5. Therefore, when the fingerprint recognition unit 100 is installed on the light-emitting surface of the display module 5, it is necessary to set the orthographic projection of the transmitting electrode 11 and the receiving electrode 13 on the substrate of the display module 5 and the orthographic projection of the light-emitting unit of the display module 5 on the substrate of the display module 5 not to overlap, so as to realize the fingerprint recognition function while not affecting the luminous efficiency of the display device.

[0087] Optionally, when the fingerprint recognition unit 100 is disposed between the display substrate 51 and the cathode layer 59, the first field effect transistor 211, the second field effect transistor 212 in the signal conversion unit 2 and the signal output unit 3 including the first thin film transistor 31, the second thin film transistor 32 can also be disposed in the same layer as the circuit structures such as the pixel circuit and the pixel driving circuit in the display module 5. In this way, when manufacturing the circuit structures such as the pixel circuit and the pixel driving circuit, the first field effect transistor 211, the second field effect transistor 212 in the signal conversion unit 2 and the signal output unit 3 including the first thin film transistor 31 and the second thin film transistor 32 can be manufactured simultaneously, thereby reducing the process steps. In addition, the various structures in the fingerprint recognition unit 100 can also be disposed in any other film layer between the display substrate 51 and the cathode layer 59.

[0088] In a specific embodiment, Fig.10aAs shown, the fingerprint identification backplane 4 is arranged on the side of the display substrate 51 close to the cathode layer 59, the receiving electrode 13 is arranged on the side of the fingerprint identification backplane 4 away from the display substrate 51, the transmitting electrode 11 is arranged on the side of the receiving electrode 13 away from the display substrate 51, and a piezoelectric layer 12 is arranged between the transmitting electrode 11 and the receiving electrode 13. A thin film encapsulation layer (Thin Film Encapsulation, TFE) 14 is arranged on the side of the transmitting electrode 11 away from the receiving electrode 13, and the thin film encapsulation layer 14 is used to protect the transmitting electrode 11, the piezoelectric layer 12, the receiving electrode 13 and other structures. Optionally, as Fig.10b As shown, a thin film encapsulation layer 14, a transmitting electrode 11, a piezoelectric layer 12, a receiving electrode 13 and a fingerprint identification backplane 4 are sequentially arranged on a side of the cathode layer 59 away from the display substrate 51.

[0089] Optionally, in the above embodiment, the display module 5 may be an organic light-emitting diode (OLED) display panel, and the display substrate 51 may be an OLED display substrate. In addition, the display module 5 described in the above embodiment may also be any other type of display panel.

[0090] The display device of the above embodiment includes the corresponding fingerprint recognition unit in the above embodiment, and has the beneficial effects of the corresponding fingerprint recognition unit embodiment, which will not be described in detail here.

[0091] Based on the same inventive concept, corresponding to the ultrasonic fingerprint recognition circuit described in any of the above embodiments, one or more embodiments of the present disclosure further provide a driving method for the ultrasonic fingerprint recognition circuit. Fig.11 As shown, the driving method includes:

[0092] Step S101, in the transmitting stage, the ultrasonic sensor receives an input signal to generate a first ultrasonic signal for fingerprint detection.

[0093] The ultrasonic sensor 1 includes a transmitting electrode 11, a receiving electrode 13, and a piezoelectric layer 12 disposed between the transmitting electrode 11 and the receiving electrode 13. The transmitting electrode 11 is configured to receive the input signal and input a first voltage to the piezoelectric layer 12 based on the input signal; the input signal is an AC signal. The piezoelectric layer 12 is configured to emit the first ultrasonic signal in response to the first voltage, so as to detect the fingerprint of the user's finger.

[0094] Step S102, in the receiving stage, the ultrasonic sensor receives the echo signal after fingerprint detection to generate an AC echo signal and sends it to the signal conversion unit; the signal conversion unit converts the AC echo signal into a DC signal and sends it to the signal output unit; the signal output unit generates a fingerprint recognition signal based on the DC signal.

[0095] When the first ultrasonic signal reaches the user's finger, the valley ridge of the fingerprint can reflect the first ultrasonic signal to form an echo signal. When the echo signal generated by the fingerprint reflection reaches the piezoelectric layer 12, the piezoelectric layer 12 can vibrate and generate a voltage change relative to the first voltage at the interface of the piezoelectric layer 12, thereby generating an AC echo signal on the receiving electrode 13 and sending it to the signal conversion unit 2.

[0096] The signal conversion unit 2 includes an inverter 21 and a first voltage signal terminal 22 and a second voltage signal terminal 23 connected to the inverter 21. The inverter 21 is configured to generate the DC signal based on the AC echo signal, the first voltage signal input to the first voltage signal terminal 22, and the second voltage signal input to the second voltage signal terminal 23.

[0097] In this embodiment, the inverter can convert both positive voltage signals and negative voltage signals into positive voltage signals, and the inverter can play a filtering role. When converting the AC echo signal into a DC signal, the positive and negative voltages in the AC echo signal can be converted without an additional boost voltage. In this way, the transistor in the signal output unit is turned on more completely, and even if the Dbias signal with a bootstrap voltage is not provided, the negative voltage part of the AC echo signal will not be lost, thereby reducing the problem of increased process difficulty caused by designing the Dbias part and reducing the process difficulty in the circuit manufacturing process. At the same time, by using the transition zone of the inverter, that is, when the AC echo signal is between the minimum input voltage VIL and the maximum input voltage VIH of the inverter, the output DC signal also has a certain amplification effect. Among them, the amplification factor of the AC echo signal amplified by the transition zone of the inverter 21 is related to the slope of the transition zone of the inverter 21, and the DC signal output after amplification is related to the minimum output voltage VOL and the maximum output voltage VOH of the inverter 21. Therefore, the adjustment of the amplification factor can be achieved by adjusting the transition zone curve of the inverter 21 through the process.

[0098] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples. Based on the concept of the present disclosure, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present disclosure as described above, which are not provided in detail for the sake of simplicity.

[0099] In addition, to simplify the description and discussion, and in order not to make the embodiments of the present disclosure difficult to understand, the known power / ground connections to the integrated circuit (IC) chips and other components may or may not be shown in the provided figures. In addition, the device can be shown in the form of a block diagram to avoid making the embodiments of the present disclosure difficult to understand, and this also takes into account the fact that the details of the implementation of these block diagram devices are highly dependent on the platform on which the embodiments of the present disclosure will be implemented (that is, these details should be fully within the scope of understanding of those skilled in the art). Where specific details (e.g., circuits) are set forth to describe exemplary embodiments of the present disclosure, it is apparent to those skilled in the art that the embodiments of the present disclosure can be implemented without these specific details or with changes in these specific details. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0100] Although the present disclosure has been described in conjunction with specific embodiments of the present disclosure, many replacements, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory architectures (e.g., dynamic RAM (DRAM)) may use the embodiments discussed.

[0101] The embodiments of the present disclosure are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. An ultrasonic fingerprint recognition circuit, comprising: An ultrasonic sensor configured to generate a first ultrasonic signal for fingerprint detection based on an input signal, and to generate an AC echo signal based on an echo signal after fingerprint detection; A signal conversion unit, one end of which is connected to the ultrasonic sensor and configured to receive the AC echo signal and convert the AC echo signal into a DC signal; a signal output unit connected to the other end of the signal conversion unit, configured to receive the DC signal and generate a fingerprint recognition signal based on the DC signal; Wherein, the signal conversion unit includes an inverter and a first voltage signal terminal and a second voltage signal terminal connected to the inverter; The inverter is configured to: generate the DC signal based on the AC echo signal, the first voltage signal inputted by the first voltage signal terminal, and the second voltage signal inputted by the second voltage signal terminal; The inverter includes a first field effect transistor and a second field effect transistor; The control electrode of the first field effect transistor is connected to the ultrasonic sensor, the first electrode of the first field effect transistor is connected to the first voltage signal terminal, and the second electrode of the first field effect transistor is connected to the signal output unit; The control electrode of the second field effect tube is connected to the ultrasonic sensor, the first electrode of the second field effect tube is connected to the second voltage signal end, and the second electrode of the second field effect tube is connected to the signal output unit.

2. The ultrasonic fingerprint recognition circuit according to claim 1, wherein: The ultrasonic sensor comprises a transmitting electrode, a receiving electrode and a piezoelectric layer arranged between the transmitting electrode and the receiving electrode; The transmitting electrode is configured to receive the input signal and input a first voltage to the piezoelectric layer based on the input signal; the input signal is an AC signal; The piezoelectric layer is configured to transmit the first ultrasonic signal in response to the first voltage, and to generate the AC echo signal in response to the echo signal reflected by the fingerprint and output it to the signal conversion unit through the receiving electrode.

3. The ultrasonic fingerprint recognition circuit according to claim 1, wherein: One of the first field effect transistor and the second field effect transistor is a P-type field effect transistor, and the other is an N-type field effect transistor.

4. The ultrasonic fingerprint recognition circuit according to claim 1, wherein: The first electrode of the first field effect transistor and the first electrode of the second field effect transistor are sources, and the second electrode of the first field effect transistor and the second electrode of the second field effect transistor are drains.

5. The ultrasonic fingerprint recognition circuit according to claim 1, wherein: The signal output unit includes a first thin film transistor and a second thin film transistor; The control electrode of the first thin film transistor is connected to the second electrode of the first field effect transistor and the second electrode of the second field effect transistor respectively, the first electrode of the first thin film transistor is connected to the third voltage signal terminal, and the second electrode of the first thin film transistor is connected to the first electrode of the second thin film transistor; The control electrode of the second thin film transistor is connected to the fourth voltage signal terminal, and the second electrode of the second thin film transistor is connected to the signal output terminal of the signal output unit.

6. A fingerprint recognition unit, comprising at least one ultrasonic fingerprint recognition circuit according to any one of claims 1 to 5.

7. A display device, comprising a display module and the fingerprint recognition unit according to claim 6, wherein: The fingerprint recognition unit is attached to the light emitting surface or the backlight surface of the display module.

8. The display device according to claim 7, wherein: The fingerprint recognition unit includes a stacked fingerprint recognition backplane and an ultrasonic sensor film layer, wherein the fingerprint recognition backplane is arranged on one side of the display module, and the ultrasonic sensor film layer is arranged on a side of the fingerprint recognition backplane away from the display module or between the fingerprint recognition backplane and the display module.

9. The display device according to claim 7, wherein: The display module includes a display substrate, a pixel driving circuit unit and a light-emitting unit which are stacked in sequence, the light-emitting unit includes an anode layer, a light-emitting layer and a cathode layer which are stacked in sequence away from the pixel driving circuit unit, and the fingerprint recognition unit includes a fingerprint recognition backplane and an ultrasonic sensor film layer which are arranged between the display substrate and the cathode layer.

10. The display device according to claim 8 or 9, wherein: The fingerprint recognition backplane includes a signal conversion unit and a signal output unit, and the ultrasonic sensor film layer includes a transmitting electrode arranged on one side of the fingerprint recognition backplane, a receiving electrode arranged between the fingerprint recognition backplane and the transmitting electrode, and a piezoelectric layer arranged between the transmitting electrode and the receiving electrode.

11. The display device according to claim 10, wherein: The transmitting electrodes and the receiving electrodes are arranged in a one-to-one correspondence, and the orthographic projection of the transmitting electrode on the display substrate coincides with the orthographic projection of the receiving electrode on the display substrate.

12. A driving method of an ultrasonic fingerprint recognition circuit, applicable to the display device according to any one of claims 7 to 11, comprising: In the transmitting stage, the ultrasonic sensor receives an input signal to generate a first ultrasonic signal for fingerprint detection; In the receiving stage, the ultrasonic sensor receives the echo signal after fingerprint detection to generate an AC echo signal and sends it to the signal conversion unit; the signal conversion unit converts the AC echo signal into a DC signal and sends it to the signal output unit; the signal output unit generates a fingerprint recognition signal based on the DC signal.

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