Research Of Timing Control Circuits For HDR TDI-CIS

Time-delay-integration (TDI) is a kind of advanced technology which can obtain higher signal-to-noise ratio (SNR) and higher sensitivity. Traditionally, TDI is used in charge-coupled device (CCD) technology. However with the rapid development of CMOS image sensor, the TDI linear array image sensor using the standard CMOS technology has so many advantages such as the high level of integration, low power consumption, low cost and so on. All of these advantages are difficult to realize in CCD. Our group independently research and develop TDI CIS chip, so the research of this paper is on the timing control system for HDR (high dynamic range)-TDI CMOS image sensor.This paper is based on the analysis of the latest research progress of TDI CIS. First of all, the timing control circuit of 1024×128 time-delay-integration (TDI) CMOS image sensor was designed using the top-down design process, including timing control circuits of pixel array, accumulator, and column level ADC and I2C bus. Implement the synchronization of charge transfer between pixels and signal accumulation, based on along-track-rolling exposure mode and through increasing the frequency of exposure. Then, in order to raise the image quality, based on double exposure technique, the timing control circuits are optimized, and two methods are implemented to realize HDR. In addition, a self-adjust mode of integration stages is put forward, in order to better adapt to changeful target scene. This algorithm can make image sensor self-adjust to the changeful cases such as bright, dark, narrow dynamic range, large saturated area, to produce a high quality images. Finally, as to the optimized timing controller simulation, synthesis, place & route, and timing analysis, finally tape out. The self-adjust algorithm of integration stages is verified on FPGA.Timing control circuit can realize the function of TDI and HDR after post simulation combining the digital and analog circuits. Based on double-exposure technique, the optimized circuits can realize the expansion of dynamic range. The theoretical analysis shows that the maximum dynamic range is increased by 42dB, and the principle of dynamic range expansion for other structures of TDI CIS is versatile. The self-adjust algorithm of integration stages is verified on FPGA, and the integrate stages can be automatically adjusted according to the current scene in real-time, which can satisfy the requirements.