Narrowband digital phase-locked loop using delta operator filters

A phase-locked loop is a control system that has already been in use for a long time for generating an output signal which is synchronized in frequency and phase to an input signal. The superior noise immunity and tracking capability of phase-locked loop makes it very attractive device in many applications, e.g. clock and data separation, FSK demodulator and Doppler recovery. In some applications, e.g., clock recovery circuits in very high-speed data link receivers, very narrow loop bandwidth is needed. In those cases, the narrow bandwidth lowpass loop filter becomes very difficult to implement with finite precision arithmetic. The objective of this paper is to introduce the use of delta operator based lowpass filters in phase-locked loops. Implementation of phase-locked loop using the delta operator based loop filter makes VLSI realizations very feasible because those filters can be implemented with very coarse quantization in cases when the loop filter bandwidth is narrow.