A pixel unit, image sensor and control method thereof

Abstract

The present invention discloses a pixel unit, an image sensor and a control method thereof. The pixel unit comprises a diode, a photosensitive device and a first capacitor; one end of the diode is respectively connected to the photosensitive device and the first capacitor; the first capacitor is connected in parallel with the photosensitive device; the unidirectional conductive characteristic of the diode is used to replace the switch function of the traditional MOS tube, so as to simplify the circuit structure of the pixel unit, and the circuit structure of the image sensor itself is greatly simplified in conjunction with the peripheral control circuit, so as to reduce the manufacturing process requirements of the image sensor itself, simplify the manufacturing process and reduce the cost; and because no MOS tube is needed, it can be implemented on a variety of substrates, so as to further reduce the cost of the image sensor, thereby reducing the production cost of a large-area image sensor array, making the application and promotion of large-area image sensors possible.

Description

Technical Field

[0001] The present invention relates to the field of image sensors, and in particular to a pixel unit, an image sensor and a control method thereof. Background Art

[0002] Optical image sensors are mainly used in the following scenarios: RGB cameras, infrared cameras, fingerprint modules, scanners, etc. Currently, they are mainly made using CMOS and CCD processes and are high-precision image sensors. The main structure of the internal circuit of these image sensors is composed of photosensitive elements, reset switches, exposure control switches, signal amplification, line readout switches and other circuits. They are usually divided into 1T, 2T, 3T, 4T, etc. according to the number of MOS tubes required for a single pixel (several Ts refer to the number of MOS tubes placed next to a single pixel). The circuits of these MOS tubes are used as electronic switches and amplifiers to solve problems such as reset, crosstalk isolation, signal amplification, and signal readout between different pixels.

[0003] For example, the working principle of the 4T architecture circuit is: T1 is a reset transistor, used to reset the charge on the photosensitive element; T2 is an exposure time control tube, used to accurately control the exposure time of the image; T3 is a source follower, used to amplify the weak electrical signal on the photosensitive element; T4 is a row selection switch. After the switch is turned on, the signal on the current sensor will be output to the subsequent ADC, and the ADC will then sample the signal.

[0004] Although this type of image sensor composed of multiple switches has high acquisition accuracy, it uses multiple MOS tubes as switches, amplifiers, and selections on a single pixel unit, and each pixel requires multiple control lines (usually each MOS tube requires a control signal). The circuit is highly complex, the manufacturing process is complex, and the cost is high. It is not suitable for making low-cost image sensors with large areas but relatively low accuracy requirements and low speed requirements. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a pixel unit, an image sensor and a control method thereof, which can simplify the circuit structure of the image sensor and reduce the cost of the image sensor.

[0006] In order to solve the above technical problems, a technical solution adopted by the present invention is:

[0007] A pixel unit comprises a diode, a photosensitive device and a first capacitor;

[0008] One end of the diode is connected to the photosensitive device and the first capacitor respectively;

[0009] The first capacitor is connected in parallel with the photosensitive device;

[0010] During the resetting of the photosensitive device, the diode charges the first capacitor for use during the operation of the photosensitive device;

[0011] The diode is not conducting when the photosensitive device is in operation, and is conducting when transmitting an electrical signal of the photosensitive device.

[0012] Furthermore, the ends of the diode connected to the photosensitive device have the same polarity.

[0013] Furthermore, the light sensing device is a photoelectric sensor.

[0014] Furthermore, the anode of the diode is connected to the anode of the photosensitive device.

[0015] Furthermore, the capacitor is a flat plate capacitor or a parasitic capacitor of the photosensitive device.

[0016] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0017] An image sensor comprises a pixel array, a controller, a power supply, an analog-to-digital converter, a second capacitor reset switch and a second capacitor;

[0018] The pixel array comprises one or more pixel units as described above connected in parallel;

[0019] One end of the power supply is connected to the input end of the pixel array;

[0020] The output terminal of the pixel array is connected to the input terminal of the controller;

[0021] The controller includes a first output terminal, a second output terminal and a third output terminal;

[0022] The first output terminal is connected to the analog-to-digital converter;

[0023] The third output terminal is connected to the other end of the power supply;

[0024] The second capacitor is connected between the first output terminal and the third output terminal;

[0025] The second output terminal is left floating;

[0026] The second capacitor reset switch comprises a moving end and a static end;

[0027] The two ends of the second capacitor are respectively connected to the moving end and the static end of the second capacitor reset switch;

[0028] Under the control of the controller, during the resetting of the image sensor, the input terminal of the controller is connected to the third output terminal;

[0029] During the image sensor reset period, the moving end and the static end of the second capacitor reset switch are connected to discharge the second capacitor; during the image exposure period, the input end of the controller is connected to the second output end;

[0030] During signal readout, the input terminal of the controller is connected to the first output terminal;

[0031] During image exposure and signal readout, the moving end and the static end of the second capacitive reset switch are disconnected.

[0032] Further, the controller includes a data selector and a single-pole triple-throw switch;

[0033] The output terminal of the pixel array is connected to the input terminal of the data selector;

[0034] The output end of the data selector is connected to the moving end of the single-pole triple-throw switch;

[0035] The single-pole triple-throw switch includes a first fixed end, a second fixed end and a third fixed end;

[0036] The first fixed end is connected to the first output end;

[0037] The second fixed end is connected to the second output end;

[0038] The third fixed end is connected to the third output end.

[0039] Furthermore, the pixel array is arranged on a substrate;

[0040] The controller, power supply, analog-to-digital converter, second capacitor reset switch and second capacitor are all packaged on the substrate;

[0041] The pixel array includes an X-axis electrode group and a Y-axis electrode group;

[0042] The two lead pins of each pixel unit are respectively connected to the X-axis electrode group and the Y-axis electrode group;

[0043] The X-axis electrode group and the Y-axis electrode group are respectively connected to one end of the power supply and an input end of the controller.

[0044] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0045] A control method for the image sensor as described above comprises the steps of:

[0046] The controller controls the input end to be connected with the third output end to start resetting;

[0047] At the same time, the moving end of the second capacitor reset switch is controlled to be connected to the static end to discharge the second capacitor;

[0048] The selected pixel unit charges the first capacitor through the diode, and the reset ends after the first capacitor is fully charged and the second capacitor is discharged to 0V;

[0049] Controlling the movable end and the static end of the second capacitor reset switch to be disconnected;

[0050] The controller controls the input end thereof to be connected with the second input end to start image exposure;

[0051] The photosensitive device generates current after being exposed to light, and discharges the first capacitor. When the first capacitor is discharged to a preset value, the image exposure ends;

[0052] The controller controls the input end thereof to be connected to the first input, so that a path is formed between the power supply, the first capacitor and the second capacitor, and the characteristic voltage of the first capacitor is transferred to the second capacitor;

[0053] The analog-to-digital converter is controlled to read the voltage value on the second capacitor to complete signal acquisition.

[0054] The beneficial effects of the present invention are as follows: the unidirectional conductive characteristics of the diode are used to replace the switch function of the traditional MOS tube, thereby simplifying the circuit structure of the pixel unit, and cooperating with the peripheral control circuit to greatly simplify the circuit structure of the image sensor itself, thereby reducing the manufacturing process requirements of the image sensor itself, simplifying the production process and reducing the cost. Moreover, since there is no need to make a MOS tube, it can be implemented on a variety of substrates, further reducing the cost of the image sensor, thereby reducing the production cost of a large-area image sensor array, making the application and promotion of large-area image sensors possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a circuit structure diagram of a pixel unit according to an embodiment of the present invention;

[0056] Figure 2 is a circuit structure diagram of an image sensor including a single pixel unit according to an embodiment of the present invention;

[0057] Figure 3 is a circuit structure diagram of an image sensor including a plurality of pixel units according to an embodiment of the present invention;

[0058] Figure 4 is a circuit structure diagram of a packaged image sensor according to an embodiment of the present invention;

[0059] Figure 5 is a control flow chart of a single pixel unit according to an embodiment of the present invention;

[0060] Description of labels:

[0061] 100, pixel unit; 101, diode; 102, photosensitive device; 103, first capacitor;

[0062] 200, controller; 204, moving end; 205, first fixed end; 206, second fixed end; 207, third fixed end;

[0063] 201. Power supply;

[0064] 203. Analog-to-digital converter;

[0065] 202, a second capacitor;

[0066] 208, second capacitor reset switch;

[0067] 300, substrate; 301, X-axis electrode group; 302, Y-axis electrode group; 303, wiring. DETAILED DESCRIPTION

[0068] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0069] The above-mentioned pixel unit, image sensor and control method thereof can be applied to any application scenario that requires image acquisition, such as: RGB camera, infrared camera, fingerprint module, scanner, attendance equipment, etc., which will be explained below in conjunction with specific implementation.

[0070] Please refer to Figure 1 , a pixel unit 100, comprising a diode 101, a photosensitive device 102 and a first capacitor 103;

[0071] One end of the diode 101 is connected to the photosensitive device 102 and the first capacitor 103 respectively;

[0072] The first capacitor 103 is connected in parallel with the photosensitive device 102;

[0073] During the resetting period of the photosensitive device 102, the diode 101 charges the first capacitor 103 for use during the operation of the photosensitive device 102;

[0074] The diode 101 is not conducting during the operation of the photosensitive device 102, and is conducting when transmitting the electrical signal of the photosensitive device 102 and the first capacitor 103;

[0075] The ends of the diode 101 connected to the photosensitive device 102 have the same polarity;

[0076] The photosensitive device 102 is a photoelectric sensor, which is used to convert the image light signal into an electrical signal;

[0077] In another optional embodiment, the anode of the diode 101 is connected to the anode of the photosensitive device 102;

[0078] The first capacitor 103 may be a flat capacitor made of two metal plates or a parasitic capacitor of the photosensitive device 102 .

[0079] The pixel unit 100 can be used as a component of an image sensor to achieve image acquisition. In an optional embodiment, Figure 2 , Figure 3 As shown, an image sensor includes a pixel array, a controller, a power supply 201, an analog-to-digital converter ADC 203 and a second capacitor 202;

[0080] The pixel array includes one or more pixel units 100 as described above connected in parallel;

[0081] One end of the power supply 201 is connected to the input end of the pixel array;

[0082] The output terminal of the pixel array is connected to the input terminal of the controller;

[0083] The controller includes a first output terminal, a second output terminal and a third output terminal;

[0084] The first output terminal is connected to the analog-to-digital converter 203;

[0085] The third output terminal is connected to the other end of the power supply 201;

[0086] The second capacitor 202 is connected between the first output terminal and the third output terminal;

[0087] The second output terminal is left floating;

[0088] The second capacitor reset switch 208 includes a moving end and a static end;

[0089] The two ends of the second capacitor 202 are respectively connected to the moving end and the static end of the second capacitor reset switch 208;

[0090] Under the control of the controller, during the resetting of the image sensor, the input terminal of the controller is connected to the third output terminal;

[0091] During the image sensor reset period, the moving end and the static end of the second capacitor reset switch 208 are connected to discharge the second capacitor 202, so that the second capacitor 202 is discharged to 0V;

[0092] During image exposure, the input terminal of the controller is connected to the second output terminal;

[0093] During signal readout, the input terminal of the controller is connected to the first output terminal;

[0094] During image exposure and signal readout, the moving end and the static end of the second capacitance reset switch 208 are disconnected;

[0095] Figure 2 FIG. 1 is a circuit diagram of an image sensor including a single pixel unit 100. Figure 3 FIG. 1 is a circuit diagram of an image sensor including a plurality of pixel units 100;

[0096] In this embodiment, the entire circuit is divided into a pixel unit Pixel part and a control part. The control part is composed of a controller, a power supply 201, an analog-to-digital converter 203, a second capacitor reset switch 208 and a second capacitor 202. The control part is an independent control chip developed to match the pixel unit Pixel circuit structure. Since the pixel unit part does not have a physical MOS tube as a switch, it needs to be controlled by the controller to realize the reset, exposure and readout operations of the image sensor; wherein, the control of the reset, exposure and readout operations of the image sensor can be realized by software or hardware.

[0097] In an optional embodiment, the controller includes a data selector MUX and a single-pole triple-throw switch;

[0098] The output terminal of the pixel array is connected to the input terminal of the data selector;

[0099] The output end of the data selector is connected to the moving end 204 of the single-pole triple-throw switch;

[0100] The single-pole triple-throw switch includes a first fixed end 205, a second fixed end 206 and a third fixed end 207;

[0101] The first fixed end 205 is connected to the first output end;

[0102] The second fixed end 206 is connected to the second output end;

[0103] The third fixed end 207 is connected to the third output end;

[0104] Figure 2 , 3 The functions of each device are as follows:

[0105] The power supply 201 is used to provide a reset voltage to the sensor during the reset period of the sensor 102; the diode 101 is the core device of the present technology, and during the reset period, it is turned on to charge the first capacitor 103 due to the forward voltage provided by the power supply 201. During the image exposure period, because the switch 204 is disconnected and there is no loop, it plays a role in isolating other signals. During the signal readout period, it can also play a role in signal transmission in cooperation with the power supply 201 and the first capacitor 103; the photosensitive device 102 is a photoelectric sensor, which is used to convert the image light signal into an electrical signal; the capacitor 103 can be a parasitic capacitor of the photosensitive device 102 or a flat capacitor made of two metal plates, which is used to store the electrical signal after exposure; the analog switch (204, 205, 206, 207) is used to control the entire image sensor to work in reset, exposure, reading and other operations;

[0106] In order to improve the integration, the dense switch array can be implemented with a higher process (such as 180nm, 55nm and other COMS chip manufacturing processes) and integrated on an independent chip, and the independent chip integrates other components of the control part: power supply 201, analog-to-digital converter ADC 203, second capacitor 202, second capacitor reset switch 208, data selector, and then packaged together with the pixel array to form a complete system for various image acquisition application scenarios;

[0107] In an optional embodiment, if Figure 4 As shown, the pixel array is arranged on a substrate 300, and the substrate 300 can be made of materials such as glass or plastic film;

[0108] The controller 200, the power supply 201, the analog-to-digital converter ADC 203, the second capacitor reset switch 208 and the second capacitor 202 are all packaged on the substrate 300;

[0109] The pixel array includes an X-axis electrode group 301 and a Y-axis electrode group 302;

[0110] The two lead pins of each pixel unit 100 are respectively connected to the X-axis electrode group 301 and the Y-axis electrode group 302;

[0111] The X-axis electrode group 301 and the Y-axis electrode group 302 are connected to one end of the power supply 201 and the input end of the controller respectively;

[0112] The chip encapsulating the above-mentioned devices is connected to the CPU of a mobile phone or other electronic device through a cable as a system;

[0113] In another optional embodiment, Figure 5 As shown, the control process of the above-mentioned image sensor includes the following steps:

[0114] The controller controls the input terminal to be connected to the third output terminal to start resetting, at which time the switch 204 is turned to the position 207, and the power supply 201 outputs a fixed voltage;

[0115] At the same time, the moving end and the static end of the second capacitor reset switch 208 are controlled to be connected to discharge the second capacitor;

[0116] The selected pixel unit 100 charges the first capacitor 103 through the diode 101;

[0117] After the first capacitor 103 is fully charged and the second capacitor is discharged to 0V, the reset is completed;

[0118] Controlling the static end and the dynamic end of the second capacitor reset switch 208 to be disconnected;

[0119] The controller controls the input end to be connected with the second input end to start image exposure, and at this time, the switch 204 is turned to the position 206;

[0120] When the photosensitive device is exposed to light, it generates current to discharge the first capacitor 103. When the first capacitor is discharged to a preset value after a preset exposure time, the image exposure ends. At this time, the remaining voltage on the first capacitor 103 is the brightness characteristic voltage of the pixel.

[0121] The controller controls the input end to be connected to the first output end, and at this time, the switch 204 is turned to the position 205, so that the power supply 201, the first capacitor 103, and the second capacitor 202 form a path, and the power supply 201 charges the second capacitor 202 after the voltage is divided by the first capacitor 103, and the characteristic voltage of the first capacitor 103 is transferred to the second capacitor 202, and the second capacitor 202 will obtain a characteristic signal corresponding to the first capacitor 103;

[0122] The analog-to-digital converter ADC 203 is controlled to read the voltage value on the second capacitor 202 to complete signal acquisition.

[0123] In summary, the pixel unit, image sensor and control method thereof provided by the present invention divide the image sensor into a pixel component and a control component, which can be manufactured separately, so that the entire image sensor module does not need to be produced using expensive CMOS technology, and the cost can be better controlled to increase the effective area of ​​the image sensor; the pixel component uses a diode as a switching capacitor or a parasitic capacitor of a photoelectric sensor as storage, and uses the unidirectional conductive property of the diode to replace the switch function of the traditional MOS tube, thereby simplifying the circuit structure of the pixel unit, thereby simplifying the manufacturing process, reducing the production cost of a large-area image sensor array, and making the application and promotion of large-area image sensors possible. According to the designed simplified circuit structure of the pixel unit, an adapted control component part and a corresponding control method are designed, and the image sensor is controlled by the controller component to perform some switches to perform operations such as resetting, exposure and signal reading, and the control circuit of the control component part can be manufactured separately using a more integrated CMOS process, and can be manufactured using a higher process to further reduce the area and reduce the cost.

[0124] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An image sensor, characterized in that: It includes a pixel array, a controller, a power supply, an analog-to-digital converter, a second capacitor reset switch and a second capacitor; The pixel array includes one or more pixel units connected in parallel; The pixel unit includes a diode, a photosensitive device and a first capacitor; one end of the diode is connected to the photosensitive device and the first capacitor respectively; the first capacitor is connected in parallel with the photosensitive device; during the resetting of the photosensitive device, the diode charges the first capacitor for use during the operation of the photosensitive device; the diode is not turned on during the operation of the photosensitive device, and is turned on when transmitting the electrical signal of the photosensitive device; One end of the power supply is connected to the input end of the pixel array; The output terminal of the pixel array is connected to the input terminal of the controller; The controller includes a first output terminal, a second output terminal and a third output terminal; The first output terminal is connected to the analog-to-digital converter; The third output terminal is connected to the other end of the power supply; The second capacitor is connected between the first output terminal and the third output terminal; The second output terminal is left floating; The second capacitor reset switch comprises a moving end and a static end; The two ends of the second capacitor are respectively connected to the moving end and the static end of the second capacitor reset switch; Under the control of the controller, during the resetting of the image sensor, the input terminal of the controller is connected to the third output terminal; During the image reset period, the moving end and the static end of the second capacitor reset switch are connected to discharge the second capacitor; During image exposure, the input terminal of the controller is connected to the second output terminal; During signal readout, the input terminal of the controller is connected to the first output terminal; During the image exposure period and the signal readout period, the moving end and the static end of the second capacitive reset switch are disconnected.

2. The image sensor according to claim 1, characterized in that The controller includes a data selector and a single-pole triple-throw switch; The output terminal of the pixel array is connected to the input terminal of the data selector; The output end of the data selector is connected to the moving end of the single-pole triple-throw switch; The single-pole triple-throw switch includes a first fixed end, a second fixed end and a third fixed end; The first fixed end is connected to the first output end; The second fixed end is connected to the second output end; The third fixed end is connected to the third output end.

3. The image sensor according to claim 1 or 2, characterized in that: The pixel array is arranged on a substrate; The controller, power supply, analog-to-digital converter, second capacitor reset switch and second capacitor are all packaged on the substrate; The pixel array includes an X-axis electrode group and a Y-axis electrode group; The two lead pins of each pixel unit are respectively connected to the X-axis electrode group and the Y-axis electrode group; The X-axis electrode group and the Y-axis electrode group are respectively connected to one end of the power supply and an input end of the controller.

4. The image sensor according to claim 1, characterized in that The ends of the diode connected to the photosensitive device have the same polarity.

5. The image sensor according to claim 1, characterized in that The light sensing device is a photoelectric sensor.

6. The image sensor according to claim 4 or 5, characterized in that: The anode of the diode is connected to the anode of the photosensitive device.

7. The image sensor according to any one of claims 1, 4 or 5, characterized in that: The first capacitor is a flat plate capacitor or a parasitic capacitor of the photosensitive device.

8. A method for controlling an image sensor according to any one of claims 1 to 7, characterized in that: Includes steps: The controller controls the input end to be connected to the third output end to start resetting; At the same time, the moving end of the second capacitor reset switch is controlled to be connected to the static end to discharge the second capacitor; The selected pixel unit charges the first capacitor through the diode, and the reset ends after the first capacitor is fully charged and the second capacitor is discharged to 0V; Controlling the movable end and the static end of the second capacitor reset switch to be disconnected; The controller controls the input end to be connected with the second output end to start image exposure; The photosensitive device generates current after being exposed to light, and discharges the first capacitor. When the first capacitor is discharged to a preset value, the image exposure ends; The controller controls the input terminal to be connected to the first output terminal, so that a path is formed between the power supply, the first capacitor and the second capacitor, and the characteristic voltage of the first capacitor is transferred to the second capacitor; The analog-to-digital converter is controlled to read the voltage value on the second capacitor to complete signal acquisition.

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