CMOS image sensor readout circuit and implementation method thereof

Abstract

The present invention provides a CMOS image sensor readout circuit and an implementation method thereof. In the CMOS image sensor of the present invention, a plurality of adjacent pixel units are a sub-pixel unit matrix, and the sub-pixel unit matrix has two sets of readout circuit systems. When the environmental state is a first state, the sub-pixel unit matrix is ​​merged into an equivalent to one pixel unit and read out through the first set of readout circuit systems, so as to achieve a charge / voltage conversion gain greater than or equal to 120μV / e‑; when the environmental state is a second state, the plurality of pixel units of the sub-pixel unit matrix are read out separately through the second set of readout circuit systems, so as to achieve a charge / voltage conversion gain less than or equal to 100μV / e‑. The CMOS image sensor readout circuit and the implementation method thereof of the present invention can flexibly adjust the implementation mode of the readout circuit according to the environmental state, meet the different requirements of different application scenarios, improve the imaging quality, and improve the overall performance of the image sensor.

Description

Technical Field

[0001] The invention relates to a CMOS image sensor readout circuit and a realization method thereof. Background Art

[0002] CMOS image sensors have the advantages of simple process, easy integration with other devices, small size, light weight, low power consumption and low cost. Therefore, with the development of technology, CMOS image sensors are increasingly replacing CCD image sensors in various electronic products. Currently, CMOS image sensors have been widely used in static digital cameras, camera phones, digital video cameras, medical cameras (such as gastroscopes), automotive cameras, etc.

[0003] Figure 1 The pixel structure of a common CMOS image sensor in the prior art is shown. The image sensor includes a plurality of pixel units 110 arranged in an array, and the adjacent plurality of pixel units are a sub-pixel unit matrix. A sub-pixel unit matrix 100 including four adjacent pixel units 110_a, 110_b, 110_c, and 110_d is shown here. The sub-pixel unit matrix 100 has a set of readout circuit systems, and the readout circuit system includes a transfer transistor 120, a floating diffusion area 130, a row selection transistor 140, a source follower transistor 150, and a reset transistor 160. When the light condition of the ambient state is bright, the four pixel units 110_a, 110_b, 110_c, and 110_d of the sub-pixel unit matrix 100 are read out separately through the readout circuit system to achieve higher resolution and imaging quality. However, when the light condition of the environment is dark, in order to improve the image quality, one approach in the prior art is to merge the multiple pixel units 110_a, 110_b, 110_c, 110_d in the sub-pixel unit matrix 100 and then read them out through the readout circuit system to improve the charge / voltage conversion gain and improve the image quality. In other words, the CMOS image sensor of the prior art realizes the switching of different charge / voltage conversion gains through the transistors of the same set of readout circuit system, but in fact the two readout methods are still realized by sharing the same floating diffusion area. This approach has a very limited effect on improving the charge / voltage conversion gain, and therefore has a very limited effect on improving the image quality. Therefore, the existing CMOS image sensor cannot meet the different requirements of different application scenarios, thereby affecting the overall performance of the image sensor. Summary of the invention

[0004] The purpose of the present invention is to provide a CMOS image sensor readout circuit and an implementation method thereof, which can flexibly adjust the implementation mode of the readout circuit according to the environmental state, meet the different needs of different application scenarios, improve imaging quality, and enhance the overall performance of the image sensor.

[0005] Based on the above considerations, one aspect of the present invention provides a method for implementing a readout circuit of a CMOS image sensor, wherein a plurality of adjacent pixel units in the image sensor is a sub-pixel unit matrix; wherein the sub-pixel unit matrix has two sets of readout circuit systems, and when the environmental state is a first state, the sub-pixel unit matrix is ​​merged into equivalent to one pixel unit and read out through the first set of readout circuit systems, so as to achieve a charge / voltage conversion gain greater than or equal to 120 μV / e-; when the environmental state is a second state, the plurality of pixel units of the sub-pixel unit matrix are read out separately through the second set of readout circuit systems, so as to achieve a charge / voltage conversion gain less than or equal to 100 μV / e-.

[0006] Preferably, the floating diffusion region of the first set of readout circuit systems and the floating diffusion region of the second set of readout circuit systems are not electrically connected.

[0007] Preferably, the reset transistors and source follower transistors in the two sets of readout circuit systems are independent and cannot be shared.

[0008] Preferably, when the first set of readout circuit systems is in operation, charge transfer can be achieved between the photodiodes of the plurality of pixel units of the sub-pixel unit matrix.

[0009] Preferably, the charge transfer between the photodiodes is achieved by controlling the conduction and shutdown between the photodiodes of the pixel unit through a switch transistor.

[0010] Preferably, in the circuit layout design, the gate of the transfer transistor of the second set of readout circuit system is located in the middle area of ​​the sub-pixel unit matrix; the gate of the transfer transistor of the first set of readout circuit system is located on the relatively outer side of the sub-pixel unit matrix.

[0011] Preferably, a plurality of pixel units in the sub-pixel unit matrix have color filters of the same color.

[0012] Another aspect of the present invention provides a CMOS image sensor readout circuit, wherein a plurality of adjacent pixel units in the image sensor is a sub-pixel unit matrix; wherein the sub-pixel unit matrix has two sets of readout circuit systems, the first set of readout circuits being used to combine the sub-pixel unit matrix into one pixel unit for readout when the environmental state is a first state, thereby achieving a charge / voltage conversion gain greater than or equal to 120 μV / e-; and the second set of readout circuit systems being used to read out a plurality of pixel units of the sub-pixel unit matrix separately when the environmental state is a second state, thereby achieving a charge / voltage conversion gain less than or equal to 100 μV / e-.

[0013] Preferably, the floating diffusion region of the first set of readout circuit systems and the floating diffusion region of the second set of readout circuit systems are not electrically connected.

[0014] Preferably, the reset transistors and source follower transistors in the two sets of readout circuit systems are independent and cannot be shared.

[0015] Preferably, the first set of readout circuit systems includes switching transistors arranged between the photodiodes of the plurality of pixel units of the sub-pixel unit matrix, for controlling the on and off of the photodiodes to achieve charge migration between the photodiodes.

[0016] Preferably, in the circuit layout design, the gate of the transfer transistor of the second set of readout circuit system is located in the middle area of ​​the sub-pixel unit matrix; the gate of the transfer transistor of the first set of readout circuit system is located on the relatively outer side of the sub-pixel unit matrix.

[0017] Preferably, a plurality of pixel units in the sub-pixel unit matrix have color filters of the same color.

[0018] Compared with the prior art, the adjacent multiple pixel units in the CMOS image sensor of the present invention are a sub-pixel unit matrix, and the sub-pixel unit matrix has two sets of readout circuit systems. When the environmental state is the first state, the sub-pixel unit matrix is ​​merged into an equivalent pixel unit and read out through the first set of readout circuit systems to achieve a charge / voltage conversion gain greater than or equal to 120 μV / e-; when the environmental state is the second state, the multiple pixel units of the sub-pixel unit matrix are read out separately through the second set of readout circuit systems to achieve a charge / voltage conversion gain less than or equal to 100 μV / e-. The CMOS image sensor readout circuit and its implementation method of the present invention can flexibly adjust the implementation mode of the readout circuit according to the environmental state, meet the different needs of different application scenarios, improve imaging quality, and improve the overall performance of the image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0020] Figure 1 A schematic diagram of a pixel structure of a CMOS image sensor in the prior art;

[0021] Figure 2 It is a schematic diagram of the pixel structure of the CMOS image sensor of the present invention.

[0022] In the drawings, the same or similar reference numerals denote the same or similar devices (modules) or steps throughout different drawings. DETAILED DESCRIPTION

[0023] In order to solve the problems in the above-mentioned prior art, the present invention provides a CMOS image sensor readout circuit and its implementation method. In the CMOS image sensor of the present invention, a plurality of adjacent pixel units are a sub-pixel unit matrix, and the sub-pixel unit matrix has two sets of readout circuit systems. When the environmental state is the first state, the sub-pixel unit matrix is ​​merged into one pixel unit and read out through the first set of readout circuit systems, so as to achieve a charge / voltage conversion gain greater than or equal to 120 μV / e-; when the environmental state is the second state, the plurality of pixel units of the sub-pixel unit matrix are read out separately through the second set of readout circuit systems, so as to achieve a charge / voltage conversion gain less than or equal to 100 μV / e-. The CMOS image sensor readout circuit and its implementation method of the present invention can flexibly adjust the implementation mode of the readout circuit according to the environmental state, meet the different requirements of different application scenarios, improve the imaging quality, and improve the overall performance of the image sensor.

[0024] In the following specific description of the preferred embodiments, reference will be made to the attached drawings which constitute a part of the present invention. The attached drawings show by way of example specific embodiments that can implement the present invention. The illustrative embodiments are not intended to be exhaustive of all embodiments according to the present invention. It will be appreciated that other embodiments may be utilized, and structural or logical modifications may also be made without departing from the scope of the present invention. Therefore, the following specific description is not restrictive, and the scope of the present invention is limited by the appended claims.

[0025] The present invention is described in detail below with reference to specific embodiments.

[0026] Figure 2 The pixel structure of the CMOS image sensor of the present invention is shown. The image sensor includes a plurality of pixel units 210 arranged in an array, and the adjacent plurality of pixel units are a sub-pixel unit matrix. A sub-pixel unit matrix 200 including four adjacent pixel units 210_a, 210_b, 210_c, and 210_d is shown here, and the sub-pixel unit matrix 200 has two sets of readout circuit systems. Specifically, the first set of readout circuits includes a transfer transistor 220', a floating diffusion region 230', a row selection transistor 240', a source follower transistor 250', and a reset transistor 260', and also includes a switch transistor 270' arranged between the photodiodes of the plurality of pixel units 210_a, 210_b, 210_c, and 210_d of the sub-pixel unit matrix 200, which is used to control the conduction and closing of the photodiode to realize the charge migration between the photodiodes. The second set of readout circuits includes a transfer transistor 220 , a floating diffusion region 230 , a row selection transistor 240 , a source follower transistor 250 , and a reset transistor 260 .

[0027] When the environmental state is the first state (i.e., under darker light conditions), the switch transistor 270' is turned on to realize charge migration between the photodiodes of the multiple pixel units 210_a, 210_b, 210_c, and 210_d, and the sub-pixel unit matrix 200 is merged into an equivalent pixel unit and read out through the first set of readout circuit systems to achieve a larger charge / voltage conversion gain, for example, the charge / voltage conversion gain is greater than or equal to 120 μV / e-; when the environmental state is the second state (i.e., under brighter light conditions), the photodiodes of the multiple pixel units 210_a, 210_b, 210_c, and 210_d of the sub-pixel unit matrix 200 are read out separately through the second set of readout circuit systems to ensure a higher resolution while achieving a smaller charge / voltage conversion gain, for example, the charge / voltage conversion gain is less than or equal to 100 μV / e-, so that the implementation method of the readout circuit can be flexibly adjusted according to the environmental state to meet the different needs of different application scenarios, improve the imaging quality, and improve the overall performance of the image sensor.

[0028] Preferably, Figure 2 In the circuit layout design shown, the gate of the transfer transistor 220 of the second set of readout circuit system is located in the middle area of ​​the sub-pixel unit matrix; the gate of the transfer transistor 220' of the first set of readout circuit system is located on the relatively outer side of the sub-pixel unit matrix.

[0029] Preferably, the floating diffusion region 230 ′ of the first set of readout circuit systems is not electrically connected to the floating diffusion region 230 of the second set of readout circuit systems.

[0030] Preferably, the reset transistors 260 and 260' and the source follower transistors 250 and 250' in the two readout circuit systems are independent and cannot be shared, while the row selection transistors 240 and 240' can be independent (eg Figure 2 As shown), or they may be shared (not shown). In addition, in an image sensor using a 3T structure (not shown), each set of readout circuit system also includes source follower transistors 250, 250', reset transistors 260, 260', but does not include row selection transistors 240, 240'. For structures that require more transistors, such as dual gain conversion structures, dual gain conversion (DCG) transistors (not shown) may be added to the readout circuit system.

[0031] In addition, the plurality of pixel units 210_a, 210_b, 210_c, 210_d in the sub-pixel unit matrix 200 may have color filters of the same color or color filters of different colors.

[0032] In summary, the present invention provides a CMOS image sensor readout circuit and an implementation method thereof. In the CMOS image sensor of the present invention, a plurality of adjacent pixel units are a sub-pixel unit matrix, and the sub-pixel unit matrix has two sets of readout circuit systems. When the environmental state is the first state, the sub-pixel unit matrix is ​​merged into an equivalent to one pixel unit and read out through the first set of readout circuit systems, so as to achieve a charge / voltage conversion gain greater than or equal to 120 μV / e-; when the environmental state is the second state, the plurality of pixel units of the sub-pixel unit matrix are read out separately through the second set of readout circuit systems, so as to achieve a charge / voltage conversion gain less than or equal to 100 μV / e-. The CMOS image sensor readout circuit and the implementation method thereof of the present invention can flexibly adjust the implementation mode of the readout circuit according to the environmental state, meet the different requirements of different application scenarios, improve the imaging quality, and improve the overall performance of the image sensor.

[0033] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, in any case, the embodiments should be considered exemplary and non-restrictive. Furthermore, it is apparent that the term "comprising" does not exclude other elements and steps, and the wording "a" does not exclude the plural. Multiple elements stated in a device claim may also be implemented by one element. The words first, second, etc. are used to indicate names and do not indicate any particular order.

Claims

1. A method for implementing a CMOS image sensor readout circuit, characterized in that: A plurality of adjacent pixel units in the image sensor is a sub-pixel unit matrix; The sub-pixel unit matrix has two sets of readout circuit systems, the first set of readout circuit systems includes switch transistors arranged between the photodiodes of the plurality of pixel units of the sub-pixel unit matrix, and used to control the on and off of the photodiodes to realize charge migration between the photodiodes; When the environmental state is the first state under darker light conditions, the switching transistor is turned on, and the sub-pixel unit matrix is ​​merged into an equivalent pixel unit and read out through the first set of readout circuit systems, so as to achieve a charge / voltage conversion gain greater than or equal to 120 μV / e-; when the environmental state is the second state under brighter light conditions, the multiple pixel units of the sub-pixel unit matrix are read out separately through the second set of readout circuit systems, so as to achieve a charge / voltage conversion gain less than or equal to 100 μV / e-.

2. The method for implementing the CMOS image sensor readout circuit according to claim 1, characterized in that: The floating diffusion region of the first set of readout circuitry is not electrically connected to the floating diffusion region of the second set of readout circuitry.

3. The method for implementing a CMOS image sensor readout circuit according to claim 1, characterized in that: The reset transistors and source follower transistors in the two sets of readout circuit systems are independent and cannot be shared.

4. The method for implementing a CMOS image sensor readout circuit according to claim 1, characterized in that: In the circuit layout design, the gate of the transfer transistor of the second set of readout circuit system is located in the middle area of ​​the sub-pixel unit matrix; the gate of the transfer transistor of the first set of readout circuit system is located on the relatively outer side of the sub-pixel unit matrix.

5. The method for implementing a CMOS image sensor readout circuit according to claim 1, wherein: A plurality of pixel units in the sub-pixel unit matrix have color filters of the same color.

6. A CMOS image sensor readout circuit, characterized in that: A plurality of adjacent pixel units in the image sensor is a sub-pixel unit matrix; The sub-pixel unit matrix has two sets of readout circuit systems, the first set of readout circuit systems includes switch transistors arranged between the photodiodes of the plurality of pixel units of the sub-pixel unit matrix, and used to control the on and off of the photodiodes to realize charge migration between the photodiodes; The first set of readout circuit systems is used for when the environmental state is a first state under darker light conditions, the switching transistor is turned on, the sub-pixel unit matrix is ​​merged into equivalent to one pixel unit for reading, and a charge / voltage conversion gain of greater than or equal to 120 μV / e- is achieved; the second set of readout circuit systems is used for when the environmental state is a second state under brighter light conditions, the multiple pixel units of the sub-pixel unit matrix are read out separately, and a charge / voltage conversion gain of less than or equal to 100 μV / e- is achieved.

7. The CMOS image sensor readout circuit according to claim 6, characterized in that: The floating diffusion region of the first set of readout circuitry is not electrically connected to the floating diffusion region of the second set of readout circuitry.

8. The CMOS image sensor readout circuit according to claim 6, characterized in that: The reset transistors and source follower transistors in the two sets of readout circuit systems are independent and cannot be shared.

9. The CMOS image sensor readout circuit according to claim 6, characterized in that: In the circuit layout design, the gate of the transfer transistor of the second set of readout circuit system is located in the middle area of ​​the sub-pixel unit matrix; the gate of the transfer transistor of the first set of readout circuit system is located on the relatively outer side of the sub-pixel unit matrix.

10. The CMOS image sensor readout circuit according to claim 6, characterized in that: A plurality of pixel units in the sub-pixel unit matrix have color filters of the same color.

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