Patent ID: 7289004

Claim:
A frequency modulator comprising: a low frequency component of the modulating signal, voltage controlled oscillator (VCO) for outputting a modulated carrier signal and a loop filter for outputting a steering voltage to the VCO, the VCO having a tank circuit comprising a voltage controlled capacitance, the phase lock loop circuit comprises a variable frequency divider coupled to the output of the VCO and which is arranged to vary its division ratio according to the low frequency component of the modulating signal; an external voltage controlled capacitance which is arranged to modulate its capacitance according to a high frequency component of the modulating signal, the external voltage controlled capacitance being coupled to the tank circuit; a voltage divider coupled between a non-input node of the loop filter and an input port for the high frequency component of the modulating signal; and a RF blocking device coupled between the external voltage controlled capacitance and the input port for the high frequency component of the modulating signal, wherein the phase lock loop circuit is further arranged to modulate the steering voltage to the VCO with the high frequency component of the modulating signal.