Ultrasonic sensor device and control method thereof

Abstract

The present invention relates to an ultrasonic sensor device and a control method thereof. The ultrasonic sensor device includes: a plurality of pixels, each pixel including an ultrasonic transducer; and a control circuit configured to control the plurality of pixels. Each of the plurality of pixels is configured to retain a signal received by the ultrasonic transducer therein and to transmit the signal as a response signal to the control circuit. The control circuit is configured to: obtain an excitation response signal, which is a response signal transmitted from the pixel after the ultrasonic transducer in the pixel is excited; obtain a non-excitation response signal, which is a response signal transmitted from the pixel when the ultrasonic transducer in the pixel is not excited; and correct the excitation response signal based on the non-excitation response signal.

Description

Technical Field

[0001] The present invention relates to an ultrasonic sensor device and a method of controlling the ultrasonic sensor device. Background Art

[0002] Ultrasonic sensors are used in various fields, such as non-destructive testing of objects, object detection, and fingerprint reading. For example, ultrasonic fingerprint sensors have been developed, such as integrated micro-electromechanical systems (MEMS) ultrasonic fingerprint sensors and thin-film transistor (TFT) ultrasonic sensors that utilize micro-electromechanical systems (MEMS) technology. These fingerprint sensors include a pixel array consisting of a two-dimensional array of pixels, each of which includes an ultrasonic transducer.

[0003] An example of an ultrasonic transducer is a piezoelectric element. The ultrasonic transducer in a pixel can consist of a single element capable of transmitting and receiving ultrasonic waves, or a pair of a transmitter for transmitting ultrasonic waves and a receiver for receiving ultrasonic waves. Specifically, the ultrasonic transducer transmits ultrasonic waves in response to electrical signals, and also receives ultrasonic waves reflected from an object and converts the received ultrasonic waves into electrical signals. Summary of the Invention

[0004] The inventors' research has shown that signals from pixels including ultrasound transducers tend to have a low S / N (signal / noise) ratio. The inventors have found that problems such as large low-frequency noise and large signal variations occur in measurement experiments.

[0005] An ultrasonic sensor device according to one aspect of the present invention includes: a plurality of pixels, each including an ultrasonic transducer; and a control circuit configured to control the plurality of pixels. Each of the plurality of pixels is configured to retain a signal received by the ultrasonic transducer therein and transmit the signal as a response signal to the control circuit. The control circuit is configured to: acquire an excitation response signal, which is a response signal transmitted from the pixel after the ultrasonic transducer in the pixel is excited; acquire a non-excitation response signal, which is a response signal transmitted from the pixel when the ultrasonic transducer in the pixel is not excited; and correct the excitation response signal based on the non-excitation response signal.

[0006] One aspect of the present invention is a method for controlling an ultrasonic sensor device, the ultrasonic sensor device including a plurality of pixels, each pixel including an ultrasonic transducer. The method includes: acquiring an excitation response signal, which is a response signal transmitted from the pixel after the ultrasonic transducer in the pixel is excited; acquiring a non-excitation response signal, which is a response signal transmitted from the pixel when the ultrasonic transducer in the pixel is not excited; and correcting the excitation response signal based on the non-excitation response signal.

[0007] One aspect of the present invention improves the S / N ratio in an ultrasonic sensor device.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a block diagram showing a configuration of an ultrasonic sensor device in one embodiment;

[0010] Figure 2 is a circuit diagram showing a circuit configuration of pixels on a pixel array panel in one embodiment;

[0011] Figure 3 shows a configuration example of a terminal including an ultrasonic sensor device;

[0012] Figure 4 schematically shows a cross-sectional structure of a portion of a pixel;

[0013] Figure 5 is a timing chart showing an example of a sensing operation of the ultrasonic sensor device of the present invention in one frame (one unit period);

[0014] Figure 6 Providing measurement results of the stimulus response signal in the presence and absence of the sensing target object;

[0015] Figure 7A Providing a measurement result of the difference between the stimulus response signal when the target object is present and when the target object is not present;

[0016] Figure 7B providing another measurement of the difference in stimulus response signals in the presence and absence of a sensed target object;

[0017] Figure 8 is a diagram for explaining an operation of correcting an excitation response signal using a non-excitation response signal;

[0018] Figure 9 The configuration of the comb filter is schematically shown;

[0019] Figure 10 is a diagram for explaining a method of processing a response signal of a pixel to read a fingerprint, the method including a two-step correction;

[0020] Figure 11A Providing results of a plurality of measurement series regarding the difference between the stimulus response signal Vout (object present) when the presence of a target object is sensed and the stimulus response signal Vout (no object) when the object is not present;

[0021] Figure 11B providing results of a plurality of measurement series regarding the difference between the corrected stimulus response signal ^S (object present) when the sensed target object is present and the corrected stimulus response signal ^S (no object) when the object is not present;

[0022] Figure 12 Provides measurement results on the relationship between bias pulse width Tdb and some signals including ^S (no object);

[0023] Figure 13 is a flow chart of an example of a method of controlling a fingerprint sensor device;

[0024] Figure 14 Schematically shows the Figure 13 Examples of images shown at some steps of the process flow shown;

[0025] Figure 15 schematically shows a configuration example of a pixel area divided into two sub-areas; and

[0026] Figure 16 is a sequence diagram illustrating an example of a method of driving separate pixel areas. DETAILED DESCRIPTION

[0027] The ultrasonic sensor device of the present invention is described in detail below with reference to the accompanying drawings. Components in each figure are appropriately scaled and proportioned to facilitate easy identification. Hatching in the figures is used to distinguish components and does not necessarily indicate cross-sections. Nonlinear elements used as switching or amplifying elements are called transistors. Transistors include thin-film transistors (TFTs).

[0028] The ultrasonic sensor device of the present invention is suitable for use in medical and industrial testing fields, and is used for detecting fingerprints or objects. In one embodiment of the present invention, the ultrasonic sensor device includes a pixel array composed of a plurality of array pixels. The pixel array is composed of pixels arranged in one or two dimensions.

[0029] Each pixel includes an ultrasonic transducer. The ultrasonic transducer transmits and receives ultrasonic waves. The ultrasonic transducer can consist of a single element capable of transmitting and receiving ultrasonic waves, or a pair of a transmitter for transmitting ultrasonic waves and a receiver for receiving ultrasonic waves. The frequency of the ultrasonic waves is higher than 20 kHz, or a frequency above the audible range. The ultrasonic frequency is appropriately selected for the field and use case, and can be, for example, 5 MHz. Higher frequencies, such as 20 MHz or 1000 MHz, can be selected to increase the smoothness of the ultrasonic waves.

[0030] In one embodiment of the present disclosure, the ultrasonic transducer is a piezoelectric element. The piezoelectric material of the piezoelectric element can be inorganic or organic. The ultrasonic transducer generates ultrasonic waves in response to electrical signals from a control circuit and converts the received ultrasonic waves into electrical signals. The pixels store the electrical signals converted by the ultrasonic transducer. The signals received and converted by the ultrasonic transducer are transmitted from the pixels to the control circuit as response signals.

[0031] The inventors' research has shown that signals from pixels comprising an ultrasonic transducer for transmitting and receiving ultrasound tend to have a low S / N ratio. The inventors have found that problems such as large low-frequency noise and large signal variations occur in measurement experiments.

[0032] One embodiment of the present disclosure acquires a response signal after exciting an ultrasonic transducer, and also acquires a response signal without exciting the ultrasonic transducer. The response signal after exciting is corrected using the response signal without exciting. This operation effectively removes noise from the response signal after exciting, enabling more accurate sensing of an object. In the following description, the response signal after exciting may be referred to as an excited response signal, while the response signal without exciting may be referred to as a non-excited response signal.

[0033] Device Configuration

[0034] Figure 1 This is a block diagram illustrating an example configuration of an ultrasonic sensor device according to one embodiment of the present specification. Ultrasonic sensor device 10 includes a pixel array board 11 and a control circuit. The control circuit includes a multiplexer circuit 15, a driver circuit 14, a signal detector circuit 16, and a main control circuit 18. One or more of these circuits may be excluded, or another circuit may be added. Furthermore, one or more functions of one circuit may be incorporated into another circuit.

[0035] The pixel array panel 11 includes an insulating substrate (e.g., a glass substrate) and a pixel region 12 in which pixels 13 are arranged horizontally and vertically like a matrix on the insulating substrate. The pixel array in this example is composed of pixels arranged in two dimensions, but the pixel array may also be composed of pixels arranged in one dimension.

[0036] The multiplexer circuit 15 is manufactured on the insulating substrate of the pixel array panel 11 and is connected to the Figure 1 The multiplexer circuit 15 converts the signals from the pixels in time series and outputs the converted signals to a smaller number of signal lines connected to the signal detector circuit 16 for detection.

[0037] The driver circuit 14 drives and controls the pixels 13 to transmit and receive ultrasonic waves. The multiplexer circuit 15 receives ultrasonic detection signals from the pixels 13 transmitted through the signal lines Dm and outputs them to the signal detector circuit 16. The signal detector circuit 16 detects the signals from the respective signal lines converted in time series by the multiplexer circuit 15.

[0038] The main control circuit 18 controls the driver circuit 14, the multiplexer circuit 15, and the signal detector circuit 16. The main control circuit 18 obtains and processes the response signals output from each pixel 13. In one embodiment of the present specification, the main control circuit 18 corrects the excitation response signal from each pixel using the non-excitation response signal. The details of the processing of the response signal from each pixel will be described later. The driver circuit 14, the signal detector circuit 16, and the main control circuit 18 can be mounted on the pixel array panel 11 or provided separately from the pixel array panel 11 as independent components.

[0039] Pixel configuration

[0040] Figure 2 FIG1 shows a circuit configuration of pixel 13. Pixel 13 includes a piezoelectric element PE of an ultrasonic transducer. The piezoelectric element PE has two functions: generating and receiving ultrasonic waves. One of the electrodes of the piezoelectric element PE is represented by the reference numeral TX. Electrode TX can be referred to as a transmitting electrode, and the other electrode can be referred to as a receiving electrode. In the example of element configuration described later, electrode TX is an upper electrode, and the other electrode is a lower electrode. The side farther from the insulating substrate is defined as the upper side, and the side closer to the insulating substrate is defined as the lower side.

[0041] The piezoelectric element PE induces a voltage VRX according to the received ultrasonic vibration. A pixel circuit in the ultrasonic sensor device 10 of the present invention includes three thin film transistors TR1, TR2 and TR3 and a diode D1. The semiconductor material of the thin film transistor can be low temperature polysilicon, oxide semiconductor, or amorphous silicon.

[0042] The cathode terminal of diode D1 is connected to node N1 between the gate terminal of transistor TR1 and the source / drain terminal of transistor TR3. The anode terminal of diode D1 is connected to diode bias line PA. One of the source / drain terminals of transistor TR1 is connected to power supply line PP, and the other source / drain terminal is connected to one of the source / drain terminals of transistor TR2.

[0043] The gate terminal of transistor TR2 is connected to control line Rn. The other source / drain terminal of transistor TR2 is connected to signal line Dm. The gate terminal of transistor TR3 is connected to control line Rn+1. The signal transmitted by control line Rn+1 is the same as the signal transmitted by control line Rn for the next pixel row. The source / drain terminals of transistor TR3 are connected to the anode and cathode terminals of diode D1.

[0044] Transistor TR1 (amplifier transistor) amplifies the potential at one end of the piezoelectric element PE. Transistor TR2 is a switching element and controls the output of the pixel circuit. Transistor TR3 is a switching element and resets the potential between one end of the piezoelectric element PE and the gate electrode (node ​​N1) of transistor TR1.

[0045] exist Figure 1 In the ultrasonic sensor device 10, each pixel column consisting of a plurality of vertically arranged pixels 13 has a signal line Dm. All pixels 13 in the same pixel column are connected to a single signal line Dm. This signal line Dm is connected to a multiplexer circuit 15 in an end region of the pixel array panel 11.

[0046] Component structure

[0047] Figure 3 Schematically illustrates an example configuration of a terminal including a pixel array panel 11 in one embodiment of the present specification. The terminal includes the pixel array panel 11, a display panel 31, and a touch panel 32 stacked on top of each other. The touch panel 32 can employ any type of touch detection scheme, such as a capacitive or resistive type. The display panel 31 can be an organic light-emitting diode (OLED) display panel or other type of display panel. The display panel 31 and the touch panel 32 can be controlled by the main control circuit 18 together with the pixel array panel 11.

[0048] The positional relationship between the pixel array panel 11, the display panel 31, and the touch panel 32 is not limited to Figure 3 , and can be determined as needed. For example, the pixel array plate 11 and the display panel 31 do not overlap each other, and they are arranged on the same side or different sides of the touch panel 32 so as to be away from each other in the plane (when viewed in the stacking direction). The terminal may include a stacked structure of a display panel and a touch panel, which is separated from the stacked structure of the pixel array of the ultrasonic sensor device and another touch panel. The pixel array plate 11 does not need to be laid on another functional panel such as a display panel or a touch panel.

[0049] Figure 4The cross-sectional structure of a portion of a pixel is schematically shown. The definitions of top and bottom in the following description correspond to the top and bottom of the figure. The pixel array panel 11 includes an insulating substrate 151 and a medium 200 opposite to the insulating substrate 151. The medium 200 is a flexible or rigid insulating substrate made of, for example, resin or glass. Figure 3 As shown, a stacked structure of a display panel and / or a touch panel that does not interfere with ultrasonic waves may be provided above the medium 200 or in place of the medium 200. A plurality of pixels are arranged between the insulating substrate 151 and the medium 200.

[0050] The ultrasonic waves generated by the piezoelectric element are reflected by the surface of medium 200 and return to the piezoelectric element. If an object such as human skin comes into contact with the surface of medium 200, the reflectivity of the ultrasonic waves changes. The intensity of the reflected ultrasonic waves can be used to sense the presence of human skin (or the protrusions and depressions of human skin).

[0051] The pixel includes a lower electrode 162, an upper electrode 166, and a piezoelectric material layer 165 on an insulating substrate 151. These constitute the piezoelectric element of the ultrasonic transducer. The piezoelectric material layer 165 is arranged between the upper electrode 166 and the lower electrode 162. The piezoelectric material can be organic or inorganic; for example, polyvinylidene fluoride (PVDF) or zirconium titanate (PZT) can be used. In addition, a copolymer of vinylidene fluoride (CH2CF2) and trifluoroethylene (CF2CFH), or P(VDF / TrFE), can be used.

[0052] Figure 4 In the configuration example, the upper electrodes 166 of the multiple pixels are different portions of a common electrode. In one embodiment of the present specification, the upper electrodes 166 of all pixels in the pixel array are different portions of a common electrode having a shape that completely covers the entire pixel area. The same applies to the piezoelectric material layer 165. The lower electrodes 162 are separated between the individual pixels. The multiple lower electrodes 162 are arranged above the top surface of the planarization film 161.

[0053] The upper electrode 166 is a transmitting electrode, and the lower electrode 162 is a receiving electrode. Supplying an excitation signal to the upper electrode 166 enables the piezoelectric elements of all pixels to simultaneously generate ultrasonic waves, and the lower electrode 162 receives a pixel-specific signal. The upper electrode and the piezoelectric material layer can be separated for each pixel.

[0054] The pixel includes a circuit that includes a plurality of switches. This circuit drives and controls the piezoelectric element and can be referred to as a pixel circuit. The pixel circuit is fabricated between the insulating substrate 151 and the layer of the lower electrode 162. The pixel circuit controls the potential of the lower electrode 162 and also maintains the signal received by the lower electrode 162. Figure 4The configuration example shown includes a side for generating ultrasound and receiving reflected ultrasound ( Figure 4 The upper electrode 166 on the upper side of the piezoelectric element). The layer positions of the piezoelectric element and the circuit can be reversed.

[0055] Figure 4 The pixel circuit in FIG1 includes transistor TR3 and gate electrode 157B of transistor TR1. The insulating substrate 151 is a rigid or flexible substrate made of, for example, glass or resin. An undercoat insulating layer 152 made of an insulator is provided over the insulating substrate 151, and a semiconductor active layer 155 is provided over the undercoat insulating layer 152. The semiconductor active layer 155 includes low-resistance source / drain regions and a high-resistance channel region sandwiched between the source / drain regions.

[0056] The semiconductor active layer 155 is covered by a gate insulating layer 156. A gate electrode is provided over the semiconductor active layer 155 with the gate insulating layer 156 interposed therebetween. Figure 4 The gate electrode 157A of the transistor TR3 and the gate electrode 157B of the transistor TR1 are included. An interlayer insulating film 158 is provided on the layer including the gate electrodes 157A and 157B.

[0057] Source / drain electrodes 159 and 160 are provided above the interlayer insulating film 158 in the pixel region 12. The source / drain electrodes 159 and 160 may be made of an aluminum-based alloy. The source / drain electrodes 159 and 160 are connected to the semiconductor active layer 155 through contact regions 168 and 169, which are provided in contact holes formed through the interlayer insulating film 158 and the gate insulating layer 156.

[0058] The wiring region 171 extends from the source / drain electrodes 160 of the transistor TR3 and is connected to the gate electrode 157B of the transistor TR1 via a contact region 172 provided in a contact hole of the interlayer insulating film 158. The wiring region 171 and the source / drain electrodes 160 are included in the same metal layer and are not separated.

[0059] An insulating planarization film 161 is provided on the source / drain electrodes 159 and 160 and the wiring region 171. A lower electrode 162 is provided above the insulating planarization film 161. The lower electrode 162 is connected to the source / drain electrodes 160 via a contact region provided in a contact hole of the planarization film 161. A pixel circuit is formed below the lower electrode 162.

[0060] Piezoelectric material layer 165 is provided on lower electrode 162. Piezoelectric material layer 165 is in contact with the top surface of lower electrode 162 and the top surface of planarization film 161. Upper electrode 166 is provided above piezoelectric material layer 165 and in contact with piezoelectric material layer 165. Lower electrode 162, piezoelectric material layer 165, and upper electrode 166 constitute a piezoelectric element.

[0061] Read stimulus response signal

[0062] Figure 5 1 is a timing chart showing an example of a sensing operation of the ultrasonic sensor device 10 in one frame (one unit period). The main control circuit 18 controls each pixel 13 to read its response signal in each continuous frame. Figure 5 In the described operation example, the ultrasonic sensor device 10 generates ultrasonic waves at the beginning of a frame, and receives reflected ultrasonic waves after stopping the generation of the ultrasonic waves.

[0063] A frame is a period during which response signals are read from pixels in at least a portion of a pixel array. The operation example described below simultaneously drives the piezoelectric elements PE in all pixels to generate ultrasonic waves and sequentially reads response signals from different pixel rows through each data line.

[0064] refer to Figure 5 The period from time T1 to time T2 is the ultrasonic excitation period. At time T1, the driver circuit 14 changes the potential of control lines Rn and Rn+1 from a low level to a high level. In response, transistors TR2 and TR3 turn on. The driver circuit 14 maintains the potential of diode bias line PA at a low level. As a result, the potential of the receiving electrode (node ​​N1) of the piezoelectric element PE is fixed.

[0065] After transistors TR2 and TR3 are turned on, driver circuit 14 supplies an excitation signal to the transmit electrode TX of piezoelectric element PE. In response, piezoelectric element PE begins to vibrate, generating ultrasonic waves. In this example, each transmit electrode TX of the piezoelectric elements of all pixels on pixel array panel 11 is part of a common electrode. Therefore, the piezoelectric elements of all pixels vibrate simultaneously. Subsequently, driver circuit 14 stops supplying signals to transmit electrode TX.

[0066] At time T2 after the signal for the transmission electrode TX is stopped, the driver circuit 14 changes the potential of the control lines Rn and Rn+1 from a high level to a low level. In response, the transistors TR2 and TR3 are turned off.

[0067] The piezoelectric element PE starts to receive the reflected ultrasonic wave from time T2. Since the transistor TR3 is turned off, the receiving electrode of the piezoelectric element is in a floating state, thereby generating an induced voltage VRX at the piezoelectric element PE in response to the reception of the ultrasonic wave. Figure 5In the example, if the piezoelectric element PE does not receive ultrasonic waves, the induced voltage VRX is 0. If it receives ultrasonic waves, the induced voltage VRX is an AC voltage with an effective value greater than 0. The potential of node N1 changes according to the induced voltage VRX. Node N1 is the output node of the transducer.

[0068] At time T3 later than time T2, the driver circuit 14 changes the potential of the diode bias line PA from low level to high level. The diode bias adjusts the potential of the node N1 to the optimal bias voltage of the transistor TR1 to output a response signal to the signal line Dm.

[0069] exist Figure 5 In FIG. 1 , when the induced voltage VRX is 0, the potential change at the node N1 is represented by a solid line, and when the induced voltage VRX is generated, the potential change at the node N1 is represented by a dotted line. Figure 5 As shown, the potential of node N1 varies according to the sense voltage VRX and the diode bias. The potential of node N1 increases in response to the diode bias and also in response to the sense voltage VRX. The diode bias period Tdb is an important factor in accurate sensing. This will be described in detail later.

[0070] At time T4, which is later than time T3 by a period Tdb, the driver circuit 14 changes the potential of the diode bias line PA from a high level to a low level. Consequently, the potential of the node N1 becomes floating and is maintained at an increasing potential. In other words, the pixel maintains the signal received by the piezoelectric element of the ultrasonic transducer at node N1.

[0071] The driver circuit 14 supplies a high-level pulse to the control line Rn during the subsequent period from time T5 to time T6. Consequently, transistor TR2 turns on. Transistor TR1 amplifies the signal held at node N1 and outputs a response signal to the signal line Dm. The driver circuit 14 sequentially outputs pulses to the control line Rn of different pixel rows, thereby sequentially reading response signals from the pixels connected to the signal line Dm.

[0072] Signal detector circuit 16 receives output OUT from the data line. Output OUT represents the response signal from the sequentially selected pixel. The response signal from the excited piezoelectric element is higher by ΔV than the response signal from the unexcited piezoelectric element. Voltage ΔV is a value based on factors such as the diode bias voltage, the diode bias period, and the induced voltage VRX.

[0073] Noise in stimulus-response signals

[0074] Describes the noise in the stimulus response signal. The stimulus response signal is the response signal when the ultrasonic transducer is excited. Figure 6The graph provides measurement results of the excitation response signal under the conditions of sensing the presence and absence of the target object. The horizontal axis of the graph represents time, and the vertical axis represents the voltage of the excitation response signal.

[0075] Figure 6 The stimulus response signals of different pixel rows read sequentially from one data line are provided. The measurement uses a silicon cube as the sensing target object. The same applies to the other measurement results described later. In the example of the fingerprint sensor device, the stimulus response signal from the area where the fingerprint (finger) is in contact with the touch surface exhibits a close similarity to that obtained when the sensing target object is present. Figure 6 The value of the value in , and the stimulus response signal from the area of ​​the fingerprint away from the touch surface presents a value close to that obtained when the sensing target object does not exist. Figure 6 The value of the value in .

[0076] Figure 6 Each pulse pair in the graph represents a pair of stimulus response signals for a pixel row when sensing the presence and absence of a target object. For example, the leftmost pulse pair represents the stimulus response signal for the first pixel row R1. The tenth and twelfth pulse pairs represent the stimulus response signal pairs for the tenth and twelfth pixel rows R10 and R12, respectively. In each pair, the stimulus response signal when an object is present is smaller than when the object is absent.

[0077] like Figure 6 As shown, the intensity of the stimulus response signal varies significantly between pixel rows. However, the difference in signal intensity between the presence and absence of an object is very small compared to the signal intensity.

[0078] Figure 7A and Figure 7B A measurement of the difference between the stimulus response signals in the presence and absence of a sensed target object is provided. Figure 7A and Figure 7B The results of two measurement series are provided. Each measurement result (value) is the average of the values ​​measured in 1000 frames. Each graph provides the difference between the stimulus response signals of different pixel rows read sequentially from one data line. The horizontal axis of each graph represents time, and the vertical axis represents the difference between the stimulus response signals. The difference is the value obtained by subtracting the signal value when the object is not present from the signal value when the object is present.

[0079] Figure 7A and Figure 7BEach pulse in represents the difference between the stimulus response signals from a pixel row. For example, the leftmost pulse represents the difference between the stimulus response signals of the first pixel row R1. The tenth and twelfth pulses represent the difference between the stimulus response signal pairs of the tenth and twelfth pixel rows, respectively. As described above, since the stimulus response signal when an object is present is smaller than the signal when the object is not present, the pulse values ​​are negative.

[0080] like Figure 7A and Figure 7B As shown, the difference between the stimulus response signals for each pixel row varies significantly depending on the measurement. In addition, in each measurement series, the difference between the stimulus response signals varies significantly depending on the pixel row. Figure 7A Taking the measurement results in as an example, the absolute value of the difference between the stimulus response signals of the pixel row R1 is much smaller than the absolute value of the difference between the stimulus response signals of the pixel row R10 and the stimulus response signals of R12.

[0081] As understood above, the excitation response signal includes low-frequency noise. This noise may interfere with the accurate sensing of the ultrasonic sensor device. One embodiment of the present specification obtains the response signal when the ultrasonic transducer is not excited, i.e., the non-excitation response signal, and uses the non-excitation response information to correct the excitation response signal. This operation effectively removes noise from the excitation response signal.

[0082] Correction of response signal

[0083] Figure 8 1 is a diagram for explaining an operation of correcting an excitation response signal using a non-excitation response signal. Figure 8 The time variation of some signals in two consecutive frames is schematically shown. Specifically, Figure 8 The time variation of the signal supplied to the transmitting electrode TX, the response signal Vout(t) output from the data line, the response signal Vout(t-τ) in the previous frame period, and the difference between the response signals in the two frames (Vout(t-τ)–Vout(t)) is shown, where τ represents the frame period.

[0084] Figure 8 In the example in FIG, the transmission electrode TX is excited only in the odd-numbered frames and is not excited in the even-numbered frames. The processing of the odd-numbered frames and the processing of the even-numbered frames are repeated.

[0085] Specifically, the main control circuit 18 supplies an excitation signal to the piezoelectric element to generate ultrasonic waves, and then reads a response signal Vout(t) from each pixel in an odd-numbered frame. The response signal is an excitation response signal. As an example, Figure 8The excitation response signals are shown read from three pixels PX1, PX2 and PX3. Each excitation response signal comprises a true (original) signal S caused by reflected ultrasonic waves in response to an object (including the absence of the object) and noise N.

[0086] In the next even-numbered frame, the main control circuit 18 reads the response signal Vout(t) from each pixel without supplying an excitation signal to the piezoelectric element. The response signal is a non-excitation response signal. As an example, Figure 8 The non-stimulation response signals are read from three pixels PX1, PX2 and PX3. Each non-stimulation response signal does not include a signal S that responds to an object, but is composed only of noise N.

[0087] The main control circuit 18 corrects the stimulus response signal in the odd frame with the non-stimulus response signal in the next even frame to obtain an estimated value ^S of the true signal S. An example of the correction is to subtract the non-stimulus response signal in the even frame from the stimulus response signal in the odd frame according to the following formula:

[0088] ^S=Vout(t-τ)-Vout(t),

[0089] Here, τ represents one frame period, and Vout(t-τ) represents a response signal at a time one frame period earlier.

[0090] As described above, the stimulus response signal Vout(t) in the odd frame includes the true signal S and noise N, while the non-stimulation response signal Vout(t) in the even frame includes only noise N. The estimated value ^S of the true signal S can be obtained by subtracting Vout(t) in the even frame from Vout(t) in the odd frame.

[0091] This signal processing (^S=Vout(t-τ)-Vout(t)) can be performed using a comb filter. Figure 9 The configuration of a comb filter is schematically shown. The comb filter includes a delay element 401 and an operator 402. The delay element 401 outputs an input signal delayed by a time τ. The operator 402 outputs a signal obtained by subtracting the input signal from the output signal of the delay element 401. The main control circuit 18 can perform this signal processing using a processor operating according to a program or a logic circuit configured to implement the arithmetic element.

[0092] The comb filter can attenuate low frequency noise without attenuating the signal component. The above correction of the stimulus response signal attenuates the DC component and the components of the noise at integer multiples of the frame frequency to substantially zero.

[0093] The above example uses the non-stimulus response signal in the next even frame to correct the stimulus response signal in the odd frame. Another example can use the non-stimulus response signal in the next odd frame to correct the stimulus response signal in the even frame. Yet another example can use the non-stimulus response signal in the odd frame to correct the stimulus response signal in the next even frame, or use the non-stimulus response signal in the even frame to correct the stimulus response signal in the next odd frame. Yet another example can use the non-stimulus response signal in one frame to correct multiple stimulus response signals, or correct the stimulus response signal in a frame that is discontinuous with the frame with the non-stimulus response signal.

[0094] In the embodiment of the present specification, the main control circuit 18 obtains a corrected excitation response signal ^S (object present) when the target object is sensed to be present, and obtains a corrected excitation response signal ^S (object absent) when the target object is not sensed to be present. The main control circuit 18 uses the response signal ^S (object absent) to correct the response signal ^S (object present). For example, the main control circuit 18 subtracts the response signal ^S (object absent) from the response signal ^S (object present).

[0095] In some applications of ultrasonic sensor devices, the response signal ^S (object present) may include fixed pattern noise (FPN). By using the response signal ^S (no object), the FPN can be effectively removed from the response signal ^S (object present).

[0096] Figure 10 is a diagram illustrating a method for processing the response signal of a pixel to read a fingerprint. The processing includes the two-step correction described above. In frame m, the main control circuit 18 reads an excitation response signal (451) from the pixel in a state where a finger is placed on the touch surface. In the next frame m+1, the main control circuit 18 reads a non-excitation response signal (453) from the pixel in a state where a finger is placed on the touch surface. In addition, the main control circuit 18 subtracts the non-excitation response signal from the excitation response signal to obtain a corrected excitation response signal (455) in a state where a finger is placed on the touch surface.

[0097] In frame n, the main control circuit 18 reads the stimulus response signal (461) from the pixel in a state where no finger is placed on the touch surface. In the next frame n+1, the main control circuit 18 reads the non-stimulation response signal (463) from the pixel in a state where no finger is placed on the touch surface. Frame n+1 may precede frame m, or frame m+1 may precede frame n. In addition, the main control circuit 18 subtracts the non-stimulation response signal from the stimulus response signal to obtain a corrected stimulus response signal (465) in a state where no finger is placed on the touch surface.

[0098] Next, the main control circuit 18 subtracts the corrected stimulus response signal ^S (no object) when no finger is placed on the touch surface from the corrected stimulus response signal ^S (object present) when a finger is placed on the touch surface (471). The main control circuit 18 compares the fingerprint image obtained from this value with a pre-stored fingerprint image to perform fingerprint verification.

[0099] The acoustic pressure received by the ultrasonic fingerprint sensor device when no finger is placed can be higher than when a finger is placed. The acoustic pressure when no finger is placed can vary depending on the ultrasonic transducer's excitation voltage or whether a surface protection film is attached. Therefore, the corrected response signal ^S (without object) can be used to more accurately correct the corrected response signal ^S (with object).

[0100] Describe the effect of using a non-stimulus response signal to correct a stimulus response signal. Figure 11A The results of multiple measurement series are provided regarding the difference between the stimulus response signal Vout (object present) when a sensing target object is present and the stimulus response signal Vout (no object) when the object is not present. The result of one measurement series is the average value of 1000 frames. The graph shows the difference between the stimulus response signals of different pixel rows read sequentially from one data line. The horizontal axis of the graph represents time, and the vertical axis represents the difference between the stimulus response signals. This difference is obtained by subtracting the value of the stimulus response signal when the object is not present from the value of the stimulus response signal when the object is present.

[0101] exist Figure 11A In the example, different pulse groups are measured from different pixel rows (pixels) via the same data line. Each pulse is obtained from one pixel row in one measurement series. As an example, two pulse groups are provided with arrowed lines. Each arrowed line represents the variation between the measurement results of one pixel row. This variation is caused by low-frequency noise. Figure 11A As further indicated in , the signal strength relationship between Vout(with object) and Vout(without object) is different depending on the measurements in some pixel rows.

[0102] Figure 11BThe results of multiple measurement series are provided regarding the difference between the corrected stimulus response signal ^S (object present) when a sensing target object is present and the corrected stimulus response signal ^S (no object) when the sensing target object is not present. The result of one measurement series is the average value of 1000 frames. The graph shows the difference between the corrected stimulus response signals of different pixel rows sequentially read from one data line. The horizontal axis of the graph represents time, and the vertical axis represents the difference between the corrected stimulus response signals. The difference is the value obtained by subtracting the value of the corrected stimulus response signal when the object is not present from the value of the corrected stimulus response signal when the object is present.

[0103] exist Figure 11B In this example, different pulse groups are measured from different pixel rows (pixels) via the same data line. Each pulse is obtained from a single pixel row within a measurement series. As an example, two pulse groups are shown with arrowed lines. Each arrowed line represents the variation between the measurement results for a pixel row. This variation is caused by low-frequency noise.

[0104] and Figure 11A Compared to the measurement results in Figure 1, the variation or low-frequency noise is significantly smaller. Specifically, the low-frequency noise is reduced from 0.91mVRMS to 0.2mVRMS. From these measurement results, it can be understood that by correcting the excitation response signal with the non-excitation response signal, the low-frequency noise can be effectively reduced.

[0105] Adjustment of diode bias period

[0106] Description used for Figure 2 Diode D1 in the pixel circuit shown adjusts the bias pulse width Tdb. When a finger is placed on the touch surface of a fingerprint sensor device, the ridges of the fingerprint come into contact with the touch surface, while the valleys move away from the touch surface. The inventors' research has shown that the relationship between the signal strength in the area where the fingerprint (object) is in contact with the touch surface and the signal strength in the area where the fingerprint is away from the touch surface can vary depending on the pulse width Tdb.

[0107] More specifically, the value (^S(object present) - ^S(no object)), or the difference in signal strength between the area where the target object is in contact with the touch surface and the area where the object is away from the touch surface, varies depending on the pulse width Tdb used for biasing. When the pulse width Tdb is at a specific value, the area where the object is in contact with the touch surface shows a larger value, and when the pulse width Tdb is at another specific value, the area where the object is in contact with the touch surface shows a smaller value.

[0108] The inventors' research shows that the event of the value (^S(object present)-^S(no object)) changing has a strong correlation with the corrected stimulus response signal ^S(no object) when the sensed target object does not exist.

[0109] Figure 12 The graph provides measurement results regarding the relationship between bias pulse width Tdb and several signals, including ΔS (no object). The horizontal axis of the graph represents bias pulse width Tdb. The left vertical axis represents the response signal Vout (no object) from the pixel when the sensing target object is not present, and the right vertical axis represents the corrected stimulus response signal ΔS (no object) from the pixel when the sensing target object is not present.

[0110] exist Figure 12 In the graph of FIG. 5 , line 501 represents the excitation response signal when the sensing target object does not exist, line 502 represents the non-excitation response signal when the sensing target object does not exist, and curve 505 represents the corrected excitation response signal ^S (no object) when the sensing target object does not exist.

[0111] Signal ^S (no object) increases and decreases as the bias pulse width Tdb increases, exhibiting local maxima and local minima. For example, region 506 surrounded by a dotted line indicates the local maximum (@Tdb=0.98), and region 507 surrounded by a dotted line indicates the local minimum (@Tdb=1.08).

[0112] When Tdb = 0.98, the signal ^S(no object) reaches a local maximum, and the value (^S(object present) - ^S(no object)) indicates that the signal in the area where the target object is in contact with the touch surface is smaller than the signal in the area where the object is away from the touch surface. When Tdb = 1.08, the signal ^S(no object) reaches a local minimum, and the value (^S(object present) - ^S(no object)) indicates that the signal in the area where the target object is in contact with the touch surface is larger than the signal in the area where the object is away from the touch surface.

[0113] In the inventors' experiments, accurate fingerprint images were acquired near these extreme values. In contrast, at intermediate values ​​away from these extreme values, such as when Tdb = 1.03, accurate fingerprint images could not be acquired. In other words, identifying the extreme values ​​of the signal ^S (no object) and selecting a value of Tdb from a predetermined range enables acquisition of an accurate image of an object.

[0114] In one embodiment of the present disclosure, the main control circuit 18 determines the bias pulse width Tdb based on the signal ^S (no object). The main control circuit 18 measures the relationship between the signal ^S (no object) and the bias pulse width Tdb and identifies an extreme value. The main control circuit 18 selects the value of the bias pulse width Tdb from a predetermined range based on the extreme value.

[0115] The signal ^S (no object) increases and decreases with the increase of the bias pulse width Tdb and oscillates with a specific period, such as Figure 12 shown. Figure 12 The oscillation period of the signal ^S (no object) in the image is 0.2 μsec. The inventors found that the oscillation period of the signal ^S (no object) becomes the same as the period of the excitation. Figure 12 Results are provided for an excitation period of 0.2 μsec and a frequency of 5 MHz. Therefore, to measure the relationship between the signal ^S (no object) and the bias pulse width Tdb and identify local maxima and minima, it is necessary to measure the signal ^S (no object) while varying the bias pulse width Tdb for at least half the excitation period.

[0116] Figure 13 FIG. 1 is a flow chart of an example of a method for controlling a fingerprint sensor device. Figure 3 As shown, the fingerprint sensor device may be included in a terminal including a touch panel 32 and a display panel 31 . Figure 14 Schematically shows the Figure 13 Examples of images shown in some steps of the process flow are shown.

[0117] like Figure 13 As shown, when the main control circuit 18 detects an event of starting to acquire a fingerprint (601), it determines whether the touch surface is touched by a sensing target object such as a finger (hereinafter, it is assumed that the object is a finger) (602). Figure 14 In FIG, the image 651 displayed provides information notifying the user to start fingerprint verification. This is an example of an event that starts acquiring a fingerprint. The main control circuit 18 can determine whether the finger is in contact with the touch surface through a signal from the touch panel 32.

[0118] If the touch surface is touched by a finger ( 602 : YES), the main control circuit 18 displays a message on the display panel 31 instructing the user to remove the finger from the touch surface ( 603 ). Figure 14 The image 652 shown in FIG. 6 is an example of the message.

[0119] If the touch surface is not touched by a finger (602: No), the main control circuit 18 measures the relationship between the bias pulse width Tdb and the signal ^S (no object) (604). For example, the main control circuit 18 acquires the signal ^S (no object) multiple times while changing the bias pulse width Tdb, and calculates the average value of the signal ^S (no object) at each value of the bias pulse width Tdb.

[0120] Next, the main control circuit 18 identifies the value of the bias pulse width Tdb when the signal ^S (no object) takes an extreme value and sets the value as the bias pulse width Tdb (605). The bias pulse width Tdb can be a value when the signal ^S (no object) takes a value close to the extreme value.

[0121] Next, the main control circuit 18 displays a message on the display panel 31 and instructs the user to place a finger on a predetermined point 654 (606). Figure 14 The image 653 shown in FIG is an example of the message. Next, the main control circuit 18 controls the pixels using the selected bias pulse width Tdb and obtains a corrected stimulus response signal ^S (object present) (607) in a state where an object (finger) exists.

[0122] Separate drive

[0123] Description of Separate Driving of the Pixel Region 12 In one embodiment of the present specification, the ultrasonic sensor device 10 divides the pixel region 12 into a plurality of sub-regions and controls the sub-regions separately. Figure 15 Schematically shows a configuration example of a pixel area 12 divided into two sub-areas. Each sub-area is a pixel group consisting of a plurality of pixels. The number of sub-areas can be selected as needed. In an embodiment of the present specification, the common electrode and the diode bias line of the piezoelectric element are separated for each sub-area, and they are driven separately. In this configuration example, the upper electrodes of all pixels included in a pixel group are part of a common electrode, and the diode bias line for the pixel group is shared by all pixels in the pixel group.

[0124] Figure 15 Common electrodes 701A and 701B and diode bias lines 703A and 703B are shown as being separated for the two sub-regions. The upper electrode 166 of each pixel in one sub-region is part of the common electrode 701A, while the upper electrode 166 of each pixel in the other sub-region is part of the common electrode 701B. As described above, excitation signals are supplied to the common electrodes 701A and 701B, respectively. Diode bias lines 703A and 703B transmit diode bias potentials, respectively.

[0125] The driver circuit for supplying the excitation signal can be prepared separately for the common electrodes 701A and 701B. Alternatively, the output from a driver circuit can be switched between the common electrodes 701A and 701B. The diode bias lines 703A and 703B for the two sub-areas are separated to be driven separately. This configuration reduces the capacitance in the common electrode (sending electrode) and the diode bias line of the pixel to achieve a lower drive load. Therefore, it is easy to achieve large-scale device. For some sub-areas, only one of the diode bias line or the common electrode can be formed separately.

[0126] Figure 16 is a sequence diagram illustrating an example of a method of driving individual pixel regions. Figure 16 Excitation signals for transmission electrodes (common electrodes) TXA and TXB in a pixel area divided into two sub-areas and response signals from pixels in the sub-areas are schematically shown.

[0127] In the period (frame) from time T50 to time T51, the main control circuit 18 supplies the excitation signal to the transmission electrode TXA in the first sub-region A and sequentially reads the excitation response signals of the pixels in the sub-region A. The response signals from the sub-region B are not read out. The processing of the first sub-region A in this frame is the same as the reference processing. Figure 2 and Figure 8 The same processing is described for frames including excitation.

[0128] In the next period (frame) from time T51 to time T52, the main control circuit 18 sequentially reads the non-excitation response signals of the pixels in the first sub-region A without supplying the excitation signal to the transmission electrode TXA in the sub-region A. The response signal from the sub-region B is not read out. The processing of the first sub-region A in this frame is the same as the reference signal. Figure 8 The same process is described for frames that do not include an excitation.

[0129] In the period (frame) from time T52 to time T53, the main control circuit 18 supplies the excitation signal to the transmission electrode TXB in the second sub-region B and sequentially reads the excitation response signals of the pixels in the sub-region B. The response signal from the sub-region A is not read out. The processing of the second sub-region B in this frame is the same as the reference processing. Figure 2 and Figure 8 The same processing is described for frames including excitation.

[0130] In the next period (frame) from time T53 to time T54, the main control circuit 18 sequentially reads the non-excitation response signals of the pixels in the second sub-region B without supplying the excitation signal to the transmission electrode TXB in the sub-region B. The response signal from the sub-region A is not read out. The processing of the second sub-region B in this frame is the same as the reference signal. Figure 8 The same process is described for the frames that do not include excitation. The process is repeated for these four frames.

[0131] The above example uses two consecutive frames to acquire the non-stimulation response signal and the stimulation response signal from one sub-region, and then performs the same operation on another sub-region using another two consecutive frames. Another example can read the stimulation response signal from one sub-region and the non-stimulation response signal from another sub-region in a single frame. In this case, separate pixel column data lines are provided for each sub-region.

[0132] For example, in the first frame, the main control circuit 18 supplies the excitation signal to the transmission electrode TXA in the first sub-region A, and does not supply the excitation signal to the transmission electrode TXB in the second sub-region B. Thereafter, the main control circuit 18 sequentially reads the excitation response signals from the pixels in the sub-region A, and also sequentially reads the non-excitation response signals from the pixels in the sub-region B.

[0133] In the next frame, the main control circuit 18 supplies the excitation signal to the transmission electrode TXB in the second sub-region B, and does not supply the excitation signal to the transmission electrode TXA in the first sub-region A. Thereafter, the main control circuit 18 sequentially reads the non-excitation response signal from the pixels in the sub-region A, and also sequentially reads the excitation response signal from the pixels in the sub-region B.

[0134] As described above, the embodiments of the present invention have been described; however, the present invention is not limited to the aforementioned embodiments. Those skilled in the art can easily modify, add, or convert each element of the aforementioned embodiments within the scope of the present invention. A portion of the configuration of one embodiment can be replaced with the configuration of another embodiment, or the configuration of one embodiment can be incorporated into the configuration of another embodiment.

Claims

1. An ultrasonic sensor device, comprising: a plurality of pixels, each pixel comprising an ultrasound transducer; as well as a control circuit configured to control the plurality of pixels, wherein each pixel of the plurality of pixels is configured to hold a signal received by the ultrasound transducer in each pixel and send the signal as a response signal to the control circuit, and Wherein, the control circuit is configured as follows: Acquiring an excitation response signal, where the excitation response signal is a response signal sent from the pixel after the ultrasonic transducer in the pixel is excited; Acquiring a non-excitation response signal, the non-excitation response signal being a response signal sent from a pixel when an ultrasonic transducer in the pixel is not excited; and The stimulus response signal is corrected based on the non-stimulus response signal.

2. The ultrasonic sensor device according to claim 1, wherein The control circuit is configured to: Acquiring a first excitation response signal and a first non-excitation response signal in a state where the presence of a target object is sensed; correcting the first stimulus response signal based on the first non-stimulus response signal; Acquiring a second excitation response signal and a second non-excitation response signal in a state where the sensing target object does not exist; correcting the second stimulus response signal based on the second non-stimulus response signal; as well as Based on a comparison result of the corrected first stimulus response signal and the corrected second stimulus response signal, a stimulus response signal caused by the sensing target object is determined.

3. The ultrasonic sensor device according to claim 1, wherein The control circuit is configured to: In each of a plurality of consecutive frames, controlling the plurality of pixels to obtain a response signal from each pixel; acquiring a stimulus-response signal in one of two consecutive frames; as well as A non-stimulation response signal is acquired in another frame of the two consecutive frames.

4. The ultrasonic sensor device according to claim 1, in, Each pixel of the plurality of pixels includes a diode having a cathode connected to an output node of the ultrasound transducer, and Wherein, the control circuit is configured as follows: supplying a bias pulse to a cathode of the diode after energizing the ultrasonic transducer; acquiring a third excitation response signal and a third non-excitation response signal in a state where the sensing target object does not exist; and A pulse width of the bias pulse is adjusted based on a difference between the third excitation response signal and the third non-excitation response signal.

5. The ultrasonic sensor device according to claim 4, wherein The control circuit is configured to: Obtaining a difference between a third excitation response signal and a third non-excitation response signal at different pulse widths of the bias pulse; identifying a relationship between a pulse width of the bias pulse and a difference between the third excitation response signal and the third non-excitation response signal; identifying extreme values ​​in the relationship; as well as The pulse width of the bias pulse is selected from a range predetermined based on the extreme value.

6. The ultrasonic sensor device according to claim 1, in, The plurality of pixels are divided into a plurality of pixel groups, Each pixel group in the plurality of pixel groups consists of one or more pixels. The ultrasonic transducer is a piezoelectric element, which includes a piezoelectric material layer and two electrodes sandwiching the piezoelectric material layer. wherein one of the electrodes of each ultrasound transducer in each pixel group is part of a common electrode in the pixel group, and The common electrodes of different pixel groups are separated from each other and configured to be controlled individually.

7. The ultrasonic sensor device according to claim 6, in, Each pixel of the plurality of pixels includes a diode having a cathode connected to an output node of the ultrasound transducer, and Wherein, diode bias lines separated from the plurality of pixel groups are arranged in the plurality of pixel groups.

8. A method of controlling an ultrasonic sensor device, the ultrasonic sensor device comprising a plurality of pixels, each pixel comprising an ultrasonic transducer, the method comprising: Acquiring an excitation response signal, where the excitation response signal is a response signal sent from the pixel after the ultrasonic transducer in the pixel is excited; Acquiring a non-excitation response signal, the non-excitation response signal being a response signal sent from a pixel when an ultrasonic transducer in the pixel is not excited; and The stimulus response signal is corrected based on the non-stimulus response signal.

Images