A time error model for time-based PWM pixel with correlated double sample in the circumstance of nonlinear response

A time error mathematical model is proposed to study the impact of nonlinear response and noises on imaging of time-based Pulse Width Modulation (PWM) pixel with the Correlated Double Sampling (CDS). The errors introduced by nonlinearity and certain noises, including fixed pattern noise (FPN), reset noise, shot noise and input-referred noise of pixel-level comparator, are studied. The relative error is impacted not only by the noise voltage, but also the comparator reference voltages, V-refl, and V-refl In the 0.18 mu m CMOS process, the simulation result shows that the noises which have the largest impact on imaging are FPN and shot noise. The higher the V-refl, and V-refl are, the smaller the error is introduced by FPN. The larger the difference between V-refl, and 14.0 is, the better the signal-to-noise ratio (SNR) is. The influence of reference voltage and clock frequency on dynamic range, and the trade-off between dynamic range and speed are also analyzed in this paper. Finally, the rules of reference voltage selection are discussed. The results can serve as a guideline to the design of the time-based PWM pixel with CDS. (C) 2013 Elsevier Ltd. All rights reserved.