Analysis of temporal noise in CMOS photodiode active pixel sensor

摘要

Temporal noise sets the fundamental limit on image sensornperformance, especially under low illumination and in videonapplications. In a CCD image sensor, temporal noise is primarily due tonthe photodetector shot noise and the output amplifier thermal and 1/fnnoise. CMOS image sensors suffer from higher noise than CCDs due to thenadditional pixel and column amplifier transistor thermal and 1/f noise.nNoise analysis is further complicated by the time-varying circuitnmodels, the fact that the reset transistor operates in subthresholdnduring reset, and the nonlinearity of the charge to voltage conversion,nwhich is becoming more pronounced as CMOS technology scales. The papernpresents a detailed and rigorous analysis of temporal noise due tonthermal and shot noise sources in CMOS active pixel sensor (APS) thatntakes into consideration these complicating factors. Performingntime-domain analysis, instead of the more traditional frequency-domainnanalysis, we find that the reset noise power due to thermal noise is atnmost half of its commonly quoted kT/C value. This result is corroboratednby several published experimental data including data presented in thisnpaper. The lower reset noise, however, comes at the expense of imagenlag. We find that alternative reset methods such as overdriving thenreset transistor gate or using a pMOS transistor can alleviate lag, butnat the expense of doubling the reset noise power. We propose a new resetnmethod that alleviates lag without increasing reset noise