Phase-locked loop frequency tracking device including a direct digital

Abstract

Disclosed is a single phase-locked loop (50, 350) providing tuning over a very large bandwidth for use in wide band carrier tracking and clock recovery systems. In a first embodiment, a DC signal is formed representative of a phase difference between an input signal changing with time and a return signal. The DC signal is applied to a narrow band voltage controlled oscillator (68) which converts the DC signal back to an AC signal. The AC signal is level shifted to form a clocking pulse for an accumulator (80) of a direct digital synthesizer (72). A digital command word is also applied to the accumulator (80), such that the digital command word represents a coarse tuning of the input frequency. The clocking pulse from the narrow band VCO (68) supplies a fine tuning of the input frequency. In a second embodiment, the DC representative phase signal is applied to an analog-to-digital converter (364) which produces an N-bit word representative of the phase difference. The change in phase alters the digital output of the analog-to-digital converter (364) which in turn is applied to the accumulator (376) of a direct digital synthesizer (370). By this invention, very wide band tracting is capable with a single phase-locked loop, thus limiting the hardware and cost.