Pixel circuit structure of ultrasonic sensor

Abstract

The invention discloses an ultrasonic sensor pixel circuit structure which comprises at least two pixel units, and each pixel unit comprises a piezoelectric material and an ultrasonic transceiving selector connected with a lower electrode of the piezoelectric material; the common circuit module comprises an ultrasonic transmitting and receiving controller, a source follower and a row and column selector; the ultrasonic transceiving selector of any pixel unit is connected to a common node of the common circuit module; the ultrasonic transceiving controller is connected with the common node and an external driving signal, a grid electrode of the source follower is connected with the common node, and an output end of the source follower is connected to the row and column selector; through the common circuit module of the plurality of pixel units, the number of transistors required by a single pixel is greatly reduced, more pixels can be accommodated under the same array area, and the pixel density of the sensor is improved, so that the resolution and the quality of sensing information such as fingerprint images are improved, and the power consumption is reduced.

Description

Technical Field

[0001] This invention relates to the field of electronic technology, and more specifically, to a pixel circuit structure for an ultrasonic sensor. Background Technology

[0002] Ultrasonic sensors utilize the electromechanical conversion properties of piezoelectric materials: under voltage excitation from a driving circuit, the sensor can emit ultrasonic signals; simultaneously, it can convert reflected ultrasonic signals back into electrical signals, thereby sensing relevant external information. Ultrasonic sensors have a wide range of applications, including biometric identification. For example, in ultrasonic fingerprint modules, they can achieve fingerprint recognition by acquiring fingerprint images. However, current ultrasonic sensors still have shortcomings in some performance aspects, thus necessitating the development of new technologies to improve their performance.

[0003] Existing ultrasonic fingerprint sensors typically employ a 3-Transistor-Active Pixel Sensor (3T-APS), where each pixel contains three transistors. The number of transistors per pixel limits the reduction of pixel area, further restricting the improvement of sensor pixel density and the reduction of power consumption. Summary of the Invention

[0004] To address at least one of the aforementioned technical problems, this invention proposes an ultrasonic sensor pixel circuit structure.

[0005] The first aspect of the present invention provides an ultrasonic sensor pixel circuit structure, comprising: At least two pixel units, each pixel unit comprising a piezoelectric material and an ultrasonic transceiver selector connected to a lower electrode of the piezoelectric material; A common circuit module, the common circuit module including an ultrasonic transceiver controller, a source follower and a row and column selector; The ultrasonic transceiver selector of any of the pixel units is connected to the common node of the shared circuit module; The ultrasonic transceiver controller is connected to the common node and the external drive signal, the gate of the source follower is connected to the common node, and the output of the source follower is connected to the row and column selector.

[0006] In a preferred embodiment of the present invention, the piezoelectric material includes an upper electrode and a lower electrode, wherein the upper electrode is connected to an Rbias driving signal.

[0007] In a preferred embodiment of the present invention, the piezoelectric material is a PVDF film, the upper electrode is a metal or alloy material, and the lower electrode is an ITO material.

[0008] In a preferred embodiment of the present invention, there are two pixel units, namely an ultrasonic transceiver selector M1 and an ultrasonic transceiver selector M2. The gates of the ultrasonic transceiver selector M1 and the ultrasonic transceiver selector M2 are respectively connected to a first selection signal SEL1 and a second selection signal SEL2.

[0009] In a preferred embodiment of the present invention, the number of pixel units is four, namely ultrasonic transceiver selector M1, ultrasonic transceiver selector M2, ultrasonic transceiver selector M6, and ultrasonic transceiver selector M7. The gates of ultrasonic transceiver selector M1, ultrasonic transceiver selector M2, ultrasonic transceiver selector M6, and ultrasonic transceiver selector M7 are respectively connected to independent first selection signal SEL1, second selection signal SEL2, third selection signal SEL3, and fourth selection signal SEL4.

[0010] In a preferred embodiment of the present invention, the ultrasonic transceiver selector is a transistor device, the first electrode of the ultrasonic transceiver selector is connected to the lower electrode of the piezoelectric material of the corresponding pixel unit, the second electrode is connected to the common node, and the gate is connected to the selection control signal.

[0011] In a preferred embodiment of the present invention, the ultrasonic transceiver controller is a transistor device, the first terminal of the ultrasonic transceiver selector is connected to an external drive signal, the second terminal is connected to the common node, and the gate is connected to a reset control signal.

[0012] In a preferred embodiment of the present invention, the source follower is a transistor device, with its first terminal connected to a power supply, its second terminal connected to the row and column selector, and its gate connected to the common node.

[0013] The technical solution of the present invention has the following advantages compared with the prior art: By using a shared circuit module for multiple pixel units, the number of transistors required for a single pixel is significantly reduced. More pixels can be accommodated in the same array area, increasing the pixel density of the sensor. This, in turn, improves the resolution and quality of sensing information such as fingerprint images and reduces power consumption. Due to the reduced number of devices per pixel, the overall transistor switching loss and static power consumption of the sensor are significantly reduced, making it more suitable for power-sensitive mobile device applications such as smartphones. Attached Figure Description

[0014] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0015] Figure 1 This is a pixel circuit diagram of the ultrasonic sensor according to Embodiment 1 of the present invention; Figure 2 This is a pixel circuit diagram of the ultrasonic sensor according to Embodiment 2 of the present invention. Detailed Implementation

[0016] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0017] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0018] Example 1 See Figure 1 As shown, this invention proposes a pixel circuit structure for an ultrasonic sensor, comprising: At least two pixel units, each pixel unit comprising a piezoelectric material and an ultrasonic transceiver selector connected to the lower electrode of the piezoelectric material; A common circuit module, which includes an ultrasonic transceiver controller, a source follower, and a row and column selector; The ultrasonic transceiver selector of any pixel unit is connected to the common node of the shared circuit module. The ultrasonic transceiver controller connects to the common node and the external drive signal, the gate of the source follower is connected to the common node, and the output of the source follower is connected to the row and column selector.

[0019] Specifically, the pixel ultrasonic transceiver controller controls the connection state between the lower electrode of the pixel and the external driving signal through its switching state, realizing the transmission and reception of ultrasonic waves by a single pixel. In the figure, 1 represents two adjacent pixel units in the ultrasonic sensor pixel array, including the proprietary structure 2 of pixel 1, the proprietary structure 3 of pixel 2, and the shared circuit 4 of the two. The proprietary structure of the pixel includes piezoelectric material and ultrasonic transceiver selectors M1 / M2. The shared circuit 4 includes the ultrasonic transceiver controller M3, the source follower M4, and the row and column selector M5. Rbias is the upper electrode drive signal, connected to the upper electrode of the piezoelectric material; the first pole of the ultrasonic transceiver controller M3 is connected to the Dbias drive signal, the second pole is connected to the PE node, and the gate is connected to the control signal RST; the first poles of the ultrasonic transceiver selectors M1 and M2 are respectively connected to the lower electrodes of their respective pixel piezoelectric materials, the second poles are connected to the PE node, and the gates are respectively connected to the control signals SEL1 and SEL2; the first pole of the source follower M4 is connected to the power supply VCC, the second pole is connected to the first pole of the row and column selector, and the gate is connected to the PE node; the first pole of the row and column selector M5 is connected to the second pole of the source follower M4, the second pole is connected to subsequent operational amplifiers and other processing circuits, and the gate is connected to the control signal EN.

[0020] Optionally, the piezoelectric material can be PVDF, and the transistor can be a MOS or TFT device.

[0021] The operation is as follows: During the transmission phase, M1 and M3 are turned on, and M2 and M5 are turned off. Pulse signals are applied to the PVDF through Rbias and Dbias, and pixel 1 generates and emits ultrasonic waves outward. During the reception phase, M1 and M5 are turned on, and M2 and M3 are turned off. The ultrasonic echo signal received by pixel 1 is transmitted to the subsequent processing circuit via M4 and M5 to complete the transmission and reception of the ultrasonic signal of pixel 1. Pixel 2 repeats the above behavior. During the transmission phase, M2 and M3 are turned on, and M1 and M5 are turned off. During the reception phase, M2 and M5 are turned on, and M1 and M3 are turned off.

[0022] Compared to the commonly used 3T-APS circuit structure, the ultrasonic sensor pixel circuit structure provided in this embodiment uses a total of 5 transistors for two pixels, averaging 2.5 transistors per pixel, thus reducing the number of transistors in the pixel circuit. On the one hand, pixel density can be increased within the same array area, improving the quality of external sensing information (such as fingerprint images); on the other hand, due to the reduced number of transistors, the overall power consumption of the sensor can be reduced, which is especially important for certain power-sensitive applications (mobile devices such as mobile phones).

[0023] According to an embodiment of the present invention, the piezoelectric material includes an upper electrode and a lower electrode, wherein the upper electrode is connected to an Rbias driving signal.

[0024] According to an embodiment of the present invention, the piezoelectric material is a PVDF thin film, the upper electrode is a metal or alloy material, and the lower electrode is an ITO material.

[0025] According to an embodiment of the present invention, there are two pixel units, namely ultrasonic transceiver selector M1 and ultrasonic transceiver selector M2. The gates of ultrasonic transceiver selector M1 and ultrasonic transceiver selector M2 are respectively connected to the first selection signal SEL1 and the second selection signal SEL2.

[0026] According to an embodiment of the present invention, the ultrasonic transceiver selector is a transistor device. The first electrode of the ultrasonic transceiver selector is connected to the lower electrode of the piezoelectric material of the corresponding pixel unit, the second electrode is connected to the common node, and the gate is connected to the selection control signal.

[0027] According to an embodiment of the present invention, the ultrasonic transceiver controller is a transistor device, the first terminal of the ultrasonic transceiver selector is connected to an external drive signal, the second terminal is connected to a common node, and the gate is connected to a reset control signal.

[0028] According to an embodiment of the present invention, the source follower is a transistor device, with its first terminal connected to a power supply, its second terminal connected to a row and column selector, and its gate connected to a common node.

[0029] Example 2 like Figure 2 As shown, the parts that are the same as those in Embodiment 1 will not be described again. The differences are as follows: There are four pixel units, namely ultrasonic transceiver selector M1, ultrasonic transceiver selector M2, ultrasonic transceiver selector M6, and ultrasonic transceiver selector M7. The gates of ultrasonic transceiver selector M1, ultrasonic transceiver selector M2, ultrasonic transceiver selector M6, and ultrasonic transceiver selector M7 are respectively connected to independent first selection signal SEL1, second selection signal SEL2, third selection signal SEL3, and fourth selection signal SEL4.

[0030] Specifically, the ultrasonic sensor pixel array comprises four adjacent pixel units, including the proprietary structure 2 of pixel 1, the proprietary structure 3 of pixel 2, the proprietary structure 5 of pixel 3, the proprietary structure 6 of pixel 4, and a shared circuit 4. The proprietary structures of each pixel include piezoelectric material and ultrasonic transceiver selectors M1 / M2 / M6 / M7. The shared circuit 4 includes an ultrasonic transceiver controller M3, a source follower M4, and a row / column selector M5. Rbias is the upper electrode drive signal, connected to the upper electrode of the piezoelectric material; the first electrode of the ultrasonic transceiver controller M3 is connected to the Dbias drive signal, the second electrode is connected to the PE node, and the gate is connected to the control signal RST; the first electrodes of the ultrasonic transceiver selectors M1, M2, M6, and M7 are respectively connected to the lower electrodes of their respective pixel piezoelectric materials, the second electrodes are connected to the PE node, and the gates are respectively connected to the control signals SEL1, SEL2, SEL3, and SEL4; the first electrode of the source follower M4 is connected to the power supply VCC, the second electrode is connected to the first electrode of the row and column selector, and the gate is connected to the PE node; the first electrode of the row and column selector M5 is connected to the second electrode of the source follower M4, the second electrode is connected to subsequent operational amplifiers and other processing circuits, and the gate is connected to the control signal EN.

[0031] Optionally, the piezoelectric material can be PVDF, and the transistor can be a MOS or TFT device.

[0032] The ultrasonic sensor pixel circuit structure provided in this embodiment uses a total of 7 transistors for four pixels, with an average of 1.75 transistors per pixel, which further reduces the number of transistors in the pixel circuit, increases the pixel density, and reduces the power consumption of the sensor.

[0033] In summary, by using a shared circuit module for multiple pixel units, the number of transistors required for a single pixel is significantly reduced. More pixels can be accommodated in the same array area, increasing the pixel density of the sensor. This, in turn, improves the resolution and quality of sensing information such as fingerprint images and reduces power consumption. Due to the reduced number of devices per pixel, the overall transistor switching losses and static power consumption of the sensor are significantly reduced, making it more suitable for power-sensitive mobile device applications such as smartphones.

[0034] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0035] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to the above embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0036] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A pixel circuit structure for an ultrasonic sensor, characterized in that, include: At least two pixel units, each pixel unit comprising a piezoelectric material and an ultrasonic transceiver selector connected to a lower electrode of the piezoelectric material; A common circuit module, the common circuit module including an ultrasonic transceiver controller, a source follower and a row and column selector; The ultrasonic transceiver selector of any of the pixel units is connected to the common node of the shared circuit module; The ultrasonic transceiver controller is connected to the common node and the external drive signal, the gate of the source follower is connected to the common node, and the output of the source follower is connected to the row and column selector.

2. The ultrasonic sensor pixel circuit structure according to claim 1, characterized in that, The piezoelectric material includes an upper electrode and a lower electrode, with the upper electrode connected to the Rbias drive signal.

3. The ultrasonic sensor pixel circuit structure according to claim 2, characterized in that, The piezoelectric material is a PVDF film, the upper electrode is a metal or alloy material, and the lower electrode is an ITO material.

4. The ultrasonic sensor pixel circuit structure according to claim 1, characterized in that, The number of pixel units is two, namely ultrasonic transceiver selector M1 and ultrasonic transceiver selector M2. The gates of ultrasonic transceiver selector M1 and ultrasonic transceiver selector M2 are respectively connected to the first selection signal SEL1 and the second selection signal SEL2.

5. The ultrasonic sensor pixel circuit structure according to claim 1, characterized in that, The number of pixel units is four, namely ultrasonic transceiver selector M1, ultrasonic transceiver selector M2, ultrasonic transceiver selector M6, and ultrasonic transceiver selector M7. The gates of ultrasonic transceiver selector M1, ultrasonic transceiver selector M2, ultrasonic transceiver selector M6, and ultrasonic transceiver selector M7 are respectively connected to independent first selection signal SEL1, second selection signal SEL2, third selection signal SEL3, and fourth selection signal SEL4.

6. The ultrasonic sensor pixel circuit structure according to claim 5, characterized in that, The ultrasonic transceiver selector is a transistor device. The first electrode of the ultrasonic transceiver selector is connected to the lower electrode of the piezoelectric material of the corresponding pixel unit, the second electrode is connected to the common node, and the gate is connected to the selection control signal.

7. The ultrasonic sensor pixel circuit structure according to claim 1, characterized in that, The ultrasonic transceiver controller is a transistor device. The first terminal of the ultrasonic transceiver selector is connected to an external drive signal, the second terminal is connected to the common node, and the gate is connected to a reset control signal.

8. The ultrasonic sensor pixel circuit structure according to claim 1, characterized in that, The source follower is a transistor device, with its first terminal connected to the power supply, its second terminal connected to the row and column selector, and its gate connected to the common node.

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