A compensation method of the excess loop delay in continuous-time complex sigma-delta modulators

Continuous-time (CT) SigmaDelta modulators seriously suffer from excess loop delay, which can not be seen in discrete-time designs. In this paper, it is shown that excess loop delay decreases the signal-to-noise ratio (SNR), input dynamic range (DR) and stability in CT complex SigmaDelta modulator with CIFF topology. A method for its compensation is presented. The proposed compensation scheme has a unity delay in front of the quantizer and complex compensation coefficients which are determined by analysis of the ideal DT loop filter transfer function. The simulation results are compared to analytical considerations.