Patent ID: 7010285

Claim:
A frequency synthesiser for generating a plurality of phase locked output frequencies comprising: a signal generator arranged to generate an output signal having an output phase and whose frequency is dependent upon an input signal and a first transfer function of the signal generator; a comparator for comparing the output signal phase with the phase of a first desired signal, whose frequency is a first multiple value of the reference frequency of a reference signal, and for generating a feedback signal which is input, in a first mode, to the signal generator as the said input signal, so as to cause the phase of the output signal of the signal generator to be locked to the phase of the first desired signal; a first switch for switching between the first mode in which the said feedback signal is supplied as the input signal of the signal generator, and a second mode, in response to said first multiple value changing to a second multiple value, thereby producing a second desired frequency, whereby in said second mode, a fixed control signal is supplied as the said input signal of the signal generator; a controller for adjusting the transfer function of the signal generator, from a first transfer function value to a second transfer function value, in the said second mode so as to cause the output frequency thereof to be altered; and a second switch for switching from the second mode to the first mode, wherein said switching is actuated when the frequency difference between the signal generator output, as determined by said second transfer function value, and the second desired frequency is below a threshold value, whereby in said first mode, the feedback signal is now generated by said signal generator with said second transfer function.