A cmos image sensor readout circuit

Abstract

A CMOS image sensor readout circuit belongs to the technical field of analog integrated circuits. The CMOS image sensor includes a plurality of pixel units, the pixel unit includes a source follower, and the substrate of the source follower is grounded; the readout circuit includes an operational amplifier, a current source and a MOS transistor M1, and the positive input terminal of the operational amplifier is connected to the output of the pixel unit terminal, its output terminal is connected to the gate of MOS transistor M1 and outputs the output signal of the CMOS image sensor, the substrate of MOS transistor M1 is grounded, its source is connected to the negative input terminal of the operational amplifier and grounded after passing through the current source, and its drain Connect the power supply voltage; MOS tube M1 is the same type as the source follower. The readout circuit proposed by the present invention is suitable for low-area and high-precision CMOS image sensors, and the voltage component lost by the level displacement of the source follower in the pixel unit is retrieved outside the pixel unit. The corrected result not only eliminates the traditional source follower. The DC offset caused by the level shift, and the small signal gain is more stable than the traditional high-precision source follower.

Description

technical field [0001] The invention belongs to the technical field of analog integrated circuits, and in particular relates to a readout circuit applied to a CMOS image sensor. Background technique [0002] With the development of CMOS technology, the size of the pixel unit of CMOS image sensor is continuously reduced, and at the same time, its performance is also continuously improved. The manufacturing cost is low, and CMOS image sensors have broad application prospects in the field of high-speed and high-precision image processing in the future. [0003] However, in some cases where the pixel unit area is required to be small, due to the limitation of the non-ideal characteristics of CMOS technology, it is difficult for CMOS image sensors to achieve high precision, which is very detrimental to the development of CMOS image sensors. One of the important non-ideal The factor is the substrate bias effect of the device. [0004] Since the source follower has the advantages...

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Problems solved by technology

[0012] It can be seen that the channel modulation effect of the MOS transistor directly affects the small signal gain of the source follower. Ideally, the gain of the buffer buffer should be 1. In fact, due to the channel length modulation effect, the source follower The gain of the small signal of the device will deviate from 1 to varying degrees, making the performance of the source follower as a buffer buffer worse, and the accuracy of the CMOS image sensor is limited

[0013] like figure 2 Shown is a way to improve the accuracy, which is mainly to connect the source and the substrate of the MOS transistor in the source follower, so that the influence of the substrate bias effect on the accuracy can be eliminated, and some high-precision The image sensor adopts this method, but this method needs to add an independent well in each pixel unit, which will undoubtedly consume a large chip area. As mentioned at the beginning, this method requires a lot of pixel unit area. High occasions won't work

[0014] Therefore, how to design a high-precision buffer buffer with the smallest possible chip area has become an unavoidable problem in CMOS image sensor technology. CMOS image sensors will never achieve high accuracy

CMOS image sensors must have a certain degree of compromise between the array size and pixel accuracy, and the application of CMOS image sensors is also greatly limited

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