DAC nonlinearity effects in a wide-band sigma-delta modulator architecture

This paper presents an alternative approach for the robust implementation of wideband sigma-delta modulators. The proposed topology consists of a pipelined cascaded sigma-delta modulator. To make quantization noise sources negligible at OSR of 8 both stages utilize multibit quantizers. To reduce sensitivity to opamp nonlinearities, both stages are implemented using the sigma-delta modulator with feedforward path. The nonlinearity effects on the modulator performance are analyzed. The simulation results show that the multibit DAC nonlinearity dominates the harmonic distortion and intermodulation distortion. The proposed sigma-delta modulator achieves an 85 dB SNR and 95 dB SFDR in the 6 MHz bandwidth, for 96 MHz sampling frequency.