A Wide-band Reference-less Bidirectional Continuous-Rate Frequency Detector

This paper presents a wide-band half-rate frequency locked loop (FLL) circuit in 180 nm CMOS process. The bidirectional FLL includes a coarse frequency detector (CFD) and a fine frequency detector (FFD) to automatically detect a change in input data rate, acquires the new frequency without the need for an external reference clock or any programming. A modified CFD is proposed to reduce the frequency acquisition time. The simulation shows the FLL achieves wide lock range of 400Mb/s-to-2.6Gb/s and frequency acquisition time of $1.73 \mu \mathrm{s}$.