Noise analysis in CMOS image sensors.

摘要

Temporal noise sets the fundamental limit on image sensor performance. In a CCD image sensor, noise is primarily due to the photodetector shot noise and the output amplifier thermal and 1/f noise. CMOS image sensors suffer from higher noise than CCDs due to the additional pixel and column amplifier transistor thermal and 1/f noise, and noise analysis is further complicated by the nonstationarity of the circuit models and the noise sources, and the nonlinearity of the charge to voltage conversion.; The thesis presents a complete and rigorous analysis of temporal noise in CMOS image sensors that takes into consideration these complicating factors. Using time domain analysis, instead of the more traditional frequency domain analysis method, we find that the reset noise power due to thermal noise is at most half of its commonly quoted KTC value. The lower reset noise, however, comes at the expense of image lag. We find that alternative reset methods such as overdriving the reset transistor gate or using a pMOS transistor can alleviate lag, but double the reset noise power. We propose a new reset method that alleviates lag without increasing reset noise.; To analyze the effect of 1/f noise on CMOS image sensors we propose a nonstationary extension of the recently developed, and generally agreed upon physical model for 1/f noise in MOS transistors. Using our model and time domain analysis, we find that the conventional frequency domain analysis results using the stationary noise model can be very inaccurate. We also show that this nonstationary model can be used to obtain accurate estimates of the effect of 1/f noise in switched circuits such as ring oscillators.