Impact of circuit nonidealities on the implementation of switched-capacitor resonators

High-speed bandpass DeltaSigma modulation is desired in applications that require analog-to-digital conversion of narrowband signals centered around intermediate frequencies. Two different approaches exist to implement the resonators needed by a switched-capacitor (SC) bandpass modulator. Both methods use a negative feedback loop around two elements. In the first approach, these elements are SC integrators, and, in the other approach, they are implemented with SC delay cells. In this paper, the impact of nonideal circuit behavior on the center frequency and quality factor of these resonators is analyzed and simulated when used at f_s/n. The nonidealities considered are finite operational amplifier gain, finite unity-gain bandwidth, and nonzero input capacitance.