Excess loop delay effects in continuous-time quadrature bandpass sigma-delta modulators

Excess loop delay is one of the main problems in continuous-time (CT) ΣΔ modulators. Previously presented papers describe this effect for CT lowpass ΣΔ modulators and for CT bandpass ΣΔ modulators. This paper, however, analytically describes and simulates the excess loop delay effect for a CT quadrature bandpass ΣΔ modulator. Furthermore, a second-order CT quadrature bandpass ΣΔ modulator using active-RC complex integrators is presented. It has a signal bandwidth of 1 MHz, centered at 1 MHz, and achieves a simulated SNDR of 80 dB at 100 MHz clock frequency.