Degradation of Alias Rejection in Continuous-Time Bandpass Delta-Sigma Converters due to Weak Loop Filter Nonlinearities

We show that the nonlinearity of the first integrator's operational transconductance amplifier (OTA) significantly degrades the alias rejection of a bandpass CTΔEM in the presence of OTA parasitics. We derive the expression for alias rejection when the OTA used in the first integrator is realized as a two stage feed-forward compensated structure. Simulation results confirm the theory.