Patent ID: 7109816

Claim:
A modulator comprising a multi-accumulator fractional-N frequency synthesiser for generating a carrier signal modulated by a modulation signal, the frequency synthesiser comprising a reference frequency generator for producing a reference signal, and first and second Phase Locked Loops ‘PLL’, said first and second PLLs including first and second Voltage Controlled Oscillators ‘VCO’, first and second variable frequency dividers whose division ratios (1/Nr, 1/Nt) are controlled by a phase modulation signal multi-accumulator sequence generators including a first and second multi-accumulator generator relative phases of said reference signal and the output of said first frequency divider for producing a first control signal through a first low pass filter, and a second phase detector responsive to the relative phases of the output of said second VCO and said second frequency divider signal for producing a second control signal, wherein said first control signal controls the frequency of said second VCO, said second control signal controls the frequency of said first VCO, said first and second frequency dividers both divide the frequency of the output of said first VCO, and the bandwidth of said first PLL is substantially smaller than the bandwidth of said second PLL.