An adaptive delta modulator with noise spectral shaping

Noise spectral shaping and performance analysis are considered in the context of Adaptive Delta Modulators (ADM´s). The goal pursued is to reduce the in-band distortion by redistributing the noise power over all the frequency band available, in a manner depending upon the feedback network. Since ADM´s generally work at a sampling frequency much higher than the Nyquist rate, one could obtain quality improvements by shifting a large amount of quantizing noise outside the base-band. Simulation results reveal that the benefit actually achievable is limited, essentially because the noise shifting causes an increase of slope overload distortion. A suitable ADM scheme with switched narrow-band Noise Shaping filter, permits to mitigate this adverse phenomenon and to achieve a subjective quality improvement.