Noise-shaping enhancement in continuous-time delta-sigma modulators

摘要

A technique is presented for designing high-order continuous-time (CT) DeltaSigma modulators with noise-transfer-function (NTF) enhancement. This enhancement is achieved by injecting the quantization noise into the forward path of the CT DeltaSigma modulator, through a passive CT filter. This passive filter introduces a real pole-zero pair into the NTF. Thus, the order of the NTF is increased, without affecting the signal transfer function (STF). The proposed NTF-enhancement technique is applied to a CT DeltaSigma modulator with a capacitive-feedforward architecture, where all feedforward paths are summed within the last integrator of the DeltaSigma loop filter. This eliminates the need for an analog summation amplifier at the output of the DeltaSigma loop filter. Behavioral and circuit-level simulation results confirm that the proposed feedforward CT DeltaSigma modulator with NTF enhancement has improved noise-shaping and stability characteristics, as compared to classical CT DeltaSigma modulators.