|
In this paper, according to the detection requirements of space infrared camera with large dynamic range and high sensitivity, a Time Delay and Integration (TDI) infrared imaging circuit with large dynamic range is introduced. The designed imaging circuit consists of 1024×7 TDI infrared detector, analog conditioning circuit and data processing circuit. 1024×7 TDI infrared detector is composed of 1024 pixel of seven photosensitive elements on which Time Delay and Integration is performed through the readout integrated circuit. In Time Delay and Integration part, an adaptive TDI stages adjustment circuit is presented, which can automatically switch seven TDI stages or one TDI stage for each pixel according to the intensity of camera detection signal，and the TDI stage mark for each pixel is provided. In analog conditioning circuit part，background subtraction circuit，programmable gain amplification circuit and 14bit ADC are designed. The background signal level is produced by 12bit DAC and the digital data of DAC is calculated from the downloaded image data of the space camera. On the basis of downloaded image data, the digital data can be dynamically uploaded to digital to analog converter by upper computer. The output analog signal of infrared detector is subtracted from background signal level, and then the effective analog signals after the background subtraction are amplified by programmable gain amplification circuit to adapt to the input scale of high precision ADC, which can reduce the equivalent input noise and can improve the dynamic range of space camera. Digital data processing circuit is implemented with FPGA. According to TDI stage mark for each pixel, the TDI stages normalization of each pixel is performed to reconstruct the pixel data in data processing circuit, and the normalized pixel data is corrected by pixel response non-uniformity correction algorithm to improve the quality of images. The designed imaging circuit system is tested, and test results show that the design scheme of the imaging circuit system is reasonable and feasible, which can effectively improve the dynamic range of space infrared camera.
|
