On Frequency Detection Capability of Full-Rate Linear and Binary Phase Detectors

Until now, it has been known that the full-rate linear and binary phase detectors (PDs) cannot detect the frequency difference between the received data and the recovered clock in clock and data recovery (CDR) loops. In this brief, we study the frequency characteristics of the full-rate linear and binary PDs and show that, unlike the binary PD, the linear PD has not only phase detection capability but also frequency detection capability intrinsically. According to our frequency-locked loop analysis, the locking trajectory of a referenceless CDR with only the full-rate linear PD in the single-loop architecture can be represented by using an exponential decay function with a single time constant. MATLAB Simulink simulations agree well with the predicted locking trajectory, which verifies that the full-rate linear PD has frequency detection capability.