A NEW DITHERING METHOD FOR SIGMA-DELTA MODULATORS

A new dithering method to remove limit-cycles in Sigma-Delta modulator s is presented. With this new method, the sequence length of a Pseudo- Noise generated dither is matched to the digital decimation filter. Th is causes the frequency spikes of the dither to coincide with the notc hes of the filter which results in total elimination of the applied di ther power. In contrast to existing dithering techniques, matched dith ering will not introduce additional inband noise. Compared to existing dithering techniques, the required dither amplitudes are relatively s mall (5%-30% FS) and may decrease with increasing oversampling ratio. Matched dithering proves to be very powerful for instrumentation appli cations.