A Digital PLL With Multitap LMS-Based Bandwidth Control

Automatic bandwidth control based on least mean-square adaptive filters has been demonstrated to desensitize the loop gain of a phase-locked loop (PLL) from process spreads, environmental variations, and channel frequency. This work extends this concept to low-jitter designs that adopt aggressive out-of-band filtering, by introducing multitap adaptive filtering. The method requires no injection of a training sequence, potentially degrading phase noise, and it is particularly suitable for bang-bang PLLs whose loop bandwidth depends on input noise. A 3.7-to-4.1-GHz PLL prototype embedding a 16-tap adaptive filter for loop-gain estimation demonstrates 150-kHz loop bandwidth over input noise and voltage supply variations, at 183-fs RMS-integrated jitter and 5.3-mW power consumption.