Finite-impulse-response (FIR) feedback in continuous-time delta-sigma converters

Finite-impulse-response (FIR) feedback was originally introduced as a way to address the problem of loopfilter nonlinearity and clock jitter in continuous-time delta-sigma modulators. It turns out that FIR feedback has other benefits - it reduces the effect of the quantizer's data-dependent jitter and enables the use of chopping 'for free'. It is an architectural technique that combines the benefits of single-bit and multibit operation, and has proven itself to be robust and scalable, applicable to ΔΣ data converters targeting a variety of specifications, and across process nodes. This paper reviews the key challenges encountered in the design of high performance delta-sigma data converters, and describes the role of FIR feedback in addressing these challenges. The prospect of using FIR feedback to achieve wide bandwidths is examined, and promising directions are reviewed.