Design Of Readout Circuit For CMOS Image Sensor Based On Visual Prosthesis

Scientists around the world are working on exploring alternative visual prosthesis to repair retinal function effective means of visual function.CMOS image sensor plays a vital role in the visual prosthesis for external signal acquisition and encoding?In this paper,the CMOS image sensor readout circuit is designed,which mainly includes pixel unit,analog signal processing circuit and analog digital conversion circuit.CSMC0.25um technology is used to design the circuit.According to the characteristics of the pixel unit,using 3T-APS high fill factor,At the same time,the column sampling amplifier is used to replace the traditional correlated double sampling circuit,which eliminates the inherent noise of the image,but also eliminates the noise caused by the offset voltage.Using chip level Successive Approx-imation Register ADC(SAR ADC)architecture including a comparator,digital to analog converter(DAC)and successive approximation register.The comparator with pre amplifier and latch device structure,and use the offset cancellation technique to achieve the required accuracy and speed;The digital to analog converter uses itself with sampling and holding function to segment charge redistribution DAC,The successive approximation shift register consists of a JK trigger,a D trigger,and a three state gate.The supply voltage is under 5V,using spectre to simulate the ADC of each module and the whole circuit.Then drawn the layout and done the post simulation.Simulation results show that the input signal frequency is 8.51 KHz standard sine signal,the sampling frequency is 142KHz,the circuit of SNR is 49.4dB,SFDR is 63.22dB,the effective number is 7.91 bits.Finally,the whole readout circuit of single pixel is simulated.