A first-order frequency-warped sigma delta modulator with improved signal-to-noise ratio

A design procedure for first-order oversampling sigma delta modulators (SDM) is proposed, which incorporates a particular frequency warping. By warping the SDM noise transfer function with positive warping parameters, the out-of-band gain can be decreased and hence stability properties can be improved. Moreover, an appropriate choice of the corresponding warped SDM loop filters leads to a signal transfer function that provides a boost in the signal band, thereby yielding an increase in signal-to-noise ratio (SNR). This paper describes the design procedure and SNR analysis for two different first-order frequency-warped SDM topologies, which require only one additional multiplier compared to the traditional SDM structure. The most promising one of these topologies is compared with the traditional first-order SDM in computer simulations using sinusoidal test signals, and yields an SNR improvement of 6 dB.