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) /spl Sigma//spl Delta/ modulators. Previously presented papers describe this effect for CT lowpass /spl Sigma//spl Delta/ modulators and for CT bandpass /spl Sigma//spl Delta/ modulators. This paper, however, analytically describes and simulates the excess loop delay effect for a CT quadrature bandpass /spl Sigma//spl Delta/ modulator. Furthermore, a second-order CT quadrature bandpass /spl Sigma//spl Delta/ 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.