Design of high order audio sigma-delta modulators with minimum weighted noise

Abstract

The design of sigma-delta modulators specifically for digital audio is discussed. Approximation techniques for the signal transfer function and the noise transfer function are described. They give an audible noise improvement over classical functions. The noise transfer function shapes the quantization noise to be least audible to the ear, while the signal transfer function is given preemphasis to match the dynamic range of the modulator to the dynamic range of typical audio sources. These functions are then transformed into switched capacitor networks for the loop filter in an LA/D converter (ADC). These give a combined improvement of 24 dB in weighted SNR for the example modulator, a seventh order, 32 times oversampling one-bit modulator. >