Patent ID: 6114902
Filing Date: 2000-09-05
Classification: H03H,H03J,H03L

Abstract:
A frequency tracking arrangement comprising:a continuously variable phase shift circuit having an input for receiving a reference frequency signal, an output providing a phase-shifted reference frequency signal and a control input, said phase shift circuit realized by an an active first order all-pass filter;a phase comparator having a first input for receiving the reference frequency signal, a second input coupled to receive the phase-shifted reference frequency signal and an output for providing a control signal obtained from a phase comparison between signals on said first input and said second input; anda feedback circuit for applying said control signal to the control input of the continuously variable phase shift circuit thereby to control, in use a value of phase shift applied by the continuously variable phase shift circuit dependent upon said phase comparison;a controllable continuous-time filter; andan adjusting circuit having:a first input coupled to the frequency tracking arrangement and receptive, in use, to the control signal;a second input responsive, in use, to an adjusting signal; andan output coupled to said controllable continuous-time filter, the output providing, in use, a filter control signal to control operational characteristics of said controllable continuous-time filter and wherein the filter control signal generated by the adjusting circuit is dependent upon said control signal and said adjusting signal.