Design Techniques for Non-Oversampled, Instantaneously Locked Clock and Data Recovery Circuits - An Overview

Traditional narrow-band clock recovery circuits such as those based on LC tanks, SAW filters or PLLs suffer from the fundamental limitation of locking (reaching steady-state operation) slowly compared to the input data rate. This is inconsequential in classical digital links where phase-coherent data flows continuously. However, if data arrives in asynchronous packets, as it does in modern communication systems such as PON’s (Passive Optical Networks), long locking times cause significant penalties in the transmission efficiency. For burst-mode applications new clock recovery methods with greater acquisition agility are needed.