Noise analysis of switched capacitor filters

The self noise output of switched-capacitor (SC) filters was examined. The two main noise sources in SC filters are switch transistors and the operational amplifiers. These noise sources were modeled as switch thermal white noise and op-amp input white noise. The existence of direct and sample-and-held noise outputs were demonstrated. The direct noise, resulting from direct circuit path, was shown to be relatively small: While the sample-and-held noise, arising from the direct noise samples, dominates the total noise output because of the aliasing effect of direct white noise. Z-domain analysis was performed on the Z-domain noise models of SC filters to evaluate the sample-and-held noise. A SC integrator, a SC biquad and a SC 7th order filter were analyzed. The predicted noise outputs of the last two filters were compared with their experimental results and good correlation between the two results has been obtained.