Design Of Wide Dynamic Range And Low Noise CMOS Image Sensor Readout Circuit

The readout circuit is the core of the CMOS image sensor,the circuit structure of the pixel unit in the readout circuit always limits the output photoelectric conversion efficiency of the photosensitive device,thereby limiting the dynamic range of the readout circuit of the CMOS image sensor.The design of wide dynamic range,low noise CMOS image sensor readout circuit becomes a research hotspot for image sensing.This paper focuses on the analysis of the existing pixel unit structure,aiming at the shortcomings of readout photoelectric conversion voltage distortion in the strong light reading of the classic image sensor readout circuit,and designing a new circuit suitable for strong light reading.The circuit adopts the method of separately sampling,storing and reading the reset stage and the integration stage,and increases the method of the comparator to select and control the working mode of the integration stage,so as to effectively broaden the reading effect of the strong light signal under the premise of suppressing the fixed mode noise,and to maintain the effect of reading under low light is not destroyed,and then increase the dynamic range of the readout circuit.At the same time,analyze and contrast the existing noise in the readout circuit.Gradually search for the best device structure and width ratio to reduce circuit noise,and design a reasonable circuit structure to suppress the fixed pattern noise,as well as designing a bandgap voltage reference with a high power supply rejection ratio to reduce the effect of ambient noise on the readout circuit.This design replaces the photodiode by an equivalent model.Based on Nuvoton 0.35pm process,use Cadence simulation software Spectre,to complete simulation and debugging about the circuit.The result shows that when integration time is set to 2μs,reset time is set to 8μs,the output voltage of the pixel unit swings among-0.046V-3.304V,and the output voltage range can be read out accurately is 0.012V-3.3V.Finally,use Laker to complete the layout of the circuit,use Calibre to complete the layout design rule check,and the circuit to layout mapping check,use Hspice to complete the post-simulation.The post-imitation results show that the range of output voltage that can be effectively read out is 0-0.7V,1.5-3V.Compared with the previous simulation result,good fit with previous simulation results.