Continuous-time ΔΣ modulators with noise-transfer-function enhancement

A technique is presented to design high-order continuous-time (CT) Delta Sigma modulators using noise-transfer-function (NTF) enhancement. This is achieved by coupling the quantization noise into the forward path of the CT Delta Sigma modulator, using a passive CT filter. This 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 Delta Sigma modulator with a feedforward architecture, where all feedforward paths are summed within the last integrator of the Delta Sigma loop filter, thereby eliminating the need for an analog summation amplifier at the quantizer input Behavioral simulation results confirm the improved noise-shaping and stability characteristics of the proposed feedforward CT Delta Sigma modulator with NTF enhancement, compared to classical CT Delta Sigma modulators.