Correlation circuit reduces oscillator perturbations in a phase locked loop

摘要

A method of controlling the oscillator in a phase locked loop (PLL) is disclosed. The PLL comprises a controlled oscillator 201, a phase detector 202 and a loop filter 203 which outputs a low frequency compensation signal in dependence upon the output of the oscillator 205 and a reference signal 206. A correlator 208 correlates an interfering signal 211 and the low frequency compensation signal from the loop filter 203. An adaptive filter 210 processes the interfering signal 211 in dependence on a correlation signal from the correlator 208 and outputs a high frequency compensation signal. A summation unit 212 combines the low frequency compensation signal from the loop filter 203 and the high frequency compensation signal from the adaptive filter 210 to form a control signal to drive the input of the oscillator. The method finds application where a phase locked loop would not otherwise be able to compensate for disturbances caused by a transmitted signal that lies outside the passband of the loop filter.