Investigation And Design Of Digital-Domain Readout Circuit Applied To TDI CMOS Image Sensor

Time delay integration (Time Delay Integration, TDI) refers to that the movingobjects are exposed repeatedly and exposure results are accumulated. Comparing tothe traditional single-line scanning image sensor, TDI CMOS technology can improvethe signal to noise ratio and sensitivity, reduce the inter-pixel response non-uniformityand the fixed image noise, the characteristics of high-resolution images can still beobtained in low light conditions, so it has a great research value.This paper introduced the principle of TDI CMOS image sensor, and the method ofexposure, the method of signal accumulating and the architecture of the image sensorare researched. The method of signal accumulation in TDI CMOS image sensormainly includes analog domain and digital domain accumulation. Because of thedisadvantage of voltage saturation in analog integrating circuit, so we focus on thekey technology of digital domain accumulation. Digital accumulation method basedon time domain ADC is proposed.The time domain ADC includes voltage to timeconverter (VTC), cyclic time to digital converter (Cyclic TDC) and time differenceamplifier (TDA). The proposed capacitor-comparator VTC can convert the analogvoltage to time defference, then the time value can be converted to the digital value bythe cyclic TDC. Digital accumulator operates and exports the digital value. Finally,the digital accumulation circuits is designed in shematic and layout,then the chip istaped out and tested.In this paper, the function of the time domain ADC was designed and verified bysimulation in GSMC0.18μm process. Its function is verified and it can convert theanalog signals to digital signals. The digital accumulator circuits were completed andthe chip was taped out in the process of GSMC0.18μm. Layout area of theaccumulation circuit for each column is30μm×6057μm.