A notch filter based frequency-difference detector and its applications

A new frequency-difference detector (FDD) based on an adaptive notch filter is proposed. The FDD is useful in decreasing acquisition times in phase-locked loop (PLL) and Costas loop based clock and carrier extraction systems. When used to aid voltage controlled oscillator (VCO) locking in a PLL, the new FDD eliminates phase errors between the input signal and the VCO output when in lock, even when a multiplying-type phase detector is used (as opposed to an edge-sensitive phase detector). This decreases jitter for low-SNR applications. Also, the control-voltage output from the FDD has substantially less ripple for a given loop bandwidth, as compared to a traditional FDD such as the quadricorrelator (QDR). This also significantly decreases the phase jitter of extracted signals