A method of tuning the frequency of a generated signal to form an output signal including: forming the generated signal at a signal generator; comparing a feedback signal with a reference signal and generating a control signal in dependence on that comparison, wherein the feedback signal is generated using the output signal; and generating the output signal by performing a frequency-dividing operation in dependence on the generated signal and a dividing factor, wherein the dividing factor is determined in dependence on the control signal.