Loop delay compensation in bandpass continuous-time ΣΔ modulators without additional feedback coefficients

Abstract

Loop-delay is one of the major sources of instability and signal-to-noise ratio degradation in continuous-time band-pass /spl Sigma//spl Delta/ modulators. In this paper, we use the modified-z-transform technique to calculate the value of the additional feedback coefficient required to compensate for the loop-delay. It is shown that, in certain conditions, this additional feedback coefficient can be removed and the loop-delay is compensated only by modifying the modulator coefficients. This is illustrated by several examples of loop-delay compensation in 2/sup nd/, 4/sup th/ and 6/sup th/ order bandpass modulators.