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CMOS图像传感器信号处理中通常采用分段电容DAC产生斜坡参考电压。研究了分段电容DAC精确的电容失配及寄生与其转换精度的关系式。基于对分段电容DAC工作原理的研究,导出了电容失配及寄生模型;针对其分数桥接电容失配、各二进制电容间的失配及寄生电容问题进行了理论分析;对分段电容DAC进行非理想因素仿真,设计了一个采用分段电容DAC的10位单斜ADC并对其进行测试,仿真和测试结果均验证了理论分析的正确性。上述理论分析结果可作为分段电容DAC的设计指导。
Slicing capacitor DACs are often used to generate the ramp reference voltage in CMOS image sensor signal processing. The relationship between the accurate capacitance mismatch of the segmented capacitor DAC and the parasitic accuracy of its conversion is studied. Based on the research of working principle of the segmented capacitance DAC, the mismatch of capacitance and parasitic model are deduced. The problem of fractional bridging capacitance mismatch, the mismatch between the binary capacitances and the parasitic capacitance are analyzed theoretically. Non-ideal factor simulation, a 10-bit single-slope ADC with a segmented capacitance DAC was designed and tested. The simulation and test results verify the correctness of the theoretical analysis. The theoretical analysis of the above results can be used as a guide to design a segmented capacitance DAC.