A semi-digital delay-locked loop using an analog-based finite state machine

This brief describes a low-power full-rate semi-digital delay-locked loop (DLL) architecture using an analog-based finite state machine (AFSM) and a polyphase filter. The AFSM architecture uses low-power analog blocks to map high-frequency loop feedback information to low frequency, thus reducing the total power required for digital signal processing and for the macro as a whole. The polyphase filter generates full-rate multiphase outputs for a phase rotator, hence a reference clock of the semi-digital DLL can be generated by any reference source including a phase-locked loop with an LC voltage-controlled oscillator. The prototype semi-digital DLL in 0.12-μm CMOS exhibits less than 10^-12 bit error rate at 3.2 Gb/s consuming 60 mW.