Effect of Mismatched Loop Delay in Continuous-Time Complex Sigma-Delta Modulators

Continuous-time (CT) complex SigmaDelta modulators seriously suffer from delay in real and imaginary feedback paths. The mismatched loop delay results in a degradation of the signal-to-noise ratio. In this paper, analytical considerations of mismatched loop delay in CT complex SigmaDelta modulators are presented. Discrete-time equivalent transfer functions to that of a CT complex loop filter are derived from continuous-discrete transformation in the complex signal domain. A solution for reducing or compensating the effect of mismatched loop delay is proposed.