Analog integrated circuits and signal processing vol:41 issue:2-3 pages:279-291
A new method is presented to predict the occurrence of unstable behavior as a function of the input amplitude in Delta-Sigma modulators using wavelets. By careful analysis it is shown that popular global analysis methods like Fourier transformation are useless in predicting unstable behavior in Delta-Sigma modulators. This necessitates the use of more time-localized analysis methods, such as wavelets. Using wavelets it is possible to calculate a number of open loop gain factors at different frequencies. These gain factors can then be used to construct a Nyquist plot, that can be used to predict whether the system is stable or not. Since only a small number of data points need to be calculated, this method is much faster than the traditional approach of long transient simulations, with only a very small error. The method works for both single-bit and multi-bit topologies and for ideal as well as non-ideal structures as is illustrated by the experimental results.