AN ALMOST LEAKAGE FREE METHOD FOR ASSESSING SIGMA-DELTA MODULATOR SPECTRA

This paper addresses the problem of spectral analysis of Sigma-Delta m odulator output spectra, Often, data containing a periodic signal are evaluated using fast-Fourier-transform (FFT) based spectral analysis, If the data set is not sampled coherently, long- and short-range leaka ge can hamper or prevent the frequency domain analysis, particularly i f frequencies near the excitation sine frequency are of interest. Tech niques such as windowing or coherent sampling help, but unfortunately may add their own effects to the spectra under scrutiny.Where coherent sampling is not easily possible, another approach to reliable spectru m analysis is a hybrid computation of the spectrum using the output bi t stream from a Sigma-Delta modulator, This will yield spectral inform ation and an assessment of modulator performance, The method is demons trated on MATLAB simulated Sigma-Delta modulator bit-stream data from a single-loop, first order modulator as well as a single-loop, third o rder modulator, both excited by a multitone sinusoidal excitation.