Study On High Dynamic Range CMOS Image Sensor

With the rapidly development of technology and people's living standards,various camera devices such as consumer-grade digital cameras and portable smart phones have become necessities.The collection and processing of image information has a very important application in aerospace,medical,military and consumer electronics.The development of modern image sensors has laid a solid foundation for these fields.At present,although CMOS image sensors have gradually replaced CCD image sensors as the market mainstream due to their advantages of easy integration,low cost,etc.,due to certain inherent deficiencies,it has restricted its further development.The dynamic range is used to define the range of light intensity that the CIS(CMOS Image Sensor)can detect.It is one of the most important technical parameters of the image sensor.Due to the limited well capacity of the pixels in the CIS,the pixels will saturate when the incident light intensity reaches a certain value.The current dynamic range of CCD and CIS is limited and it is difficult to reach the image acquisition requirements of high dynamic range scenes.Therefore,how to improve the dynamic range of CIS has become a challenging topic.This thesis innovatively proposes a new high dynamic circuit algorithm for image sensors,named a high dynamic readout circuit with dual charge transfer phase.In this paper,according to the proposed high dynamic range circuit readout algorithm,a new solution for CMOS image sensors in the field of high dynamic imaging is provided.The main work of this article mainly include the design and simulation of high dynamic readout circuits and pixel-level analog-to-digital converters.The core idea of the high dynamic readout circuit in this paper is to determine the intensity of the incident light within the pixel cell,and then feedback the judgment result back to the pixel to control the integration and charge transfer of the 4T pixel.The readout of the pixel intensity signal is divided into two stages: pre-integration stage and an integration stage.The pre-integration stage completes the judgment of the incident light intensity,and the integration stage completes sampling and reading of pixel signals and analog-to-digital conversion.This paper has completed the design and simulation verification of the high dynamic circuit readout method.Based on the novel pixel signal conversion circuit in the current CMOS image sensor architecture,that is,the pixel level analog-to-digital converter,combined with the high dynamic circuit readout method proposed in this paper,by multiplexing the comparator and latch,we can achieve the incident light intensity judgment and analog-to-digital conversion in the pixel.Based on the 0.18?m 1P4 M CMOS process,the design and simulation of the pixel-level analog-to-digital converter circuit are accomplished using Cadence.By sharing one pixel-level analog-to-digital converter with four pixels,area and power consumption are saved.The design results show that the frame rate of the image sensor reaches 100 fps,the pixel size is 15?m × 15?m,the resolution of the ADC is 8.72 bits,and the power consumption of a single pixel module is only 13.2?W.The image sensor's dynamic range is increased from 61.15 d B to 107.36 dB,achieving a 46.21 dB dynamic range enhancement.