Enhanced Dynamic Range Digital Pixel Sensor With Variable Reference Voltage

CMOS image sensors have the advantages of small volume,low cost and high imaging quality,which is widely used in industry,medical,military,consumer electronics and other fields.With the development of CMOS technology,the pulse-width-modulation CMOS digital pixel sensor has been proposed,which solves the performance reduction under low power supply.And it has the advantages of high signal-to-noise ratio,simple structure,and low power consumption.However,digital pixel sensor cannot realize high dynamic range and double sampling simultaneously.In this thesis,a multi-ramp variable reference voltage pulse-width-modulation CMOS digital pixel image sensor for improved imaging is proposed.The fixed reference voltage is replaced by a continuous reference voltage with several high and low ramps.The multi-ramp reference voltage improves the detection ability of high light and low light intensity in one pixel,which can obtain larger dynamic range with limited integration time.The exposure period of the pixel is divided into two sampling stages,and the fixed pattern noise and some random noises of the pixel can be eliminated by time-domain correlated double sampling.In this thesis,a pulse-width-modulation CMOS digital pixel image sensor behavioral model is established.The implementation algorithm of the multi-ramp reference voltage scheme and the code value processing are also proposed.With the help of MATLAB,the performance parameters such as pixel noise,dynamic range and illumination response are analyzed in detail.Optimized reference voltage design and system models are proposed.The circuit design and simulation results of some modules including pixel unit,pixel level comparator and pixel level memory are discussed.The system simulation results under SMIC0.13?m technology shows,the proposed pulse-width-modulation CMOS digital pixel image sensor with the multi-ramp reference can achieve 103.06 dB DR with CDS at 100 fps,16-bit memory depth and 1.8V power supply.The DR can be further extended to 138.49 dB with a single sampling at high light condition.FPN can drop to less than 1LSB after the CDS operation from 3.97% without CDS.