An element rotation algorithm for multi-bit DAC nonlinearities in complex bandpass /spl Delta//spl Sigma/AD modulators

This paper presents a technique for improving the resolution of complex bandpass /spl Delta//spl Sigma/ADCs which are used for wireless communication systems. Oversampling and noise-shaping are used to achieve high accuracy of a /spl Delta//spl Sigma/AD modulator. However when a multi-bit DAC is used inside a modulator, nonlinearities of the DAC are not noise-shaped and the SNR of the /spl Delta//spl Sigma/ADC degrades. For the conversion of complex intermediate frequency (IF) input signals, a complex bandpass /spl Delta//spl Sigma/AD modulator can provide superior performance to a pair of real bandpass /spl Delta//spl Sigma/AD modulators of the same order. This paper proposes a new noise-shaping algorithm-implemented by adding simple digital circuitry-to reduce the effects of nonlinearities in multi-bit DACs of complex bandpass /spl Delta//spl Sigma/AD modulators. We have performed simulation with MATLAB to verify the effectiveness of the algorithm, and the results show that the proposed algorithm can improve the SNR of a complex bandpass /spl Delta//spl Sigma/ADC with nonlinear internal multi-bit DACs.