Patent ID: 7349514

Claim:
A frequency synthesizer comprising: an input node for receiving a reference frequency signal; a variable oscillator having a first control input and a second control input, and producing an oscillator output signal whose frequency is dependent on said first and second control inputs; an analog voltage phase detector having a first phase-detection input responsive to said reference frequency signal and a second phase-detection input responsive to said oscillator output signal from said variable oscillator, said analog voltage phase detector being effective for producing a first control signal indicative of a phase difference between said reference frequency signal and said oscillator output signal, said first control signal being coupled to said first control input of said variable oscillator, wherein an analog loop is defined by the signal path along said first control signal from said analog voltage phase detector to said variable oscillator and along said oscillator output signal from said variable oscillator back to said analog voltage phase detector; a digital frequency difference detector having a first frequency-detection input responsive to said reference frequency signal and a second frequency-detection input responsive to said oscillator output signal, said digital frequency difference detector being effective for producing a second control signal indicative of a frequency difference between said reference frequency signal and said oscillator output signal, said second control signal being coupled to said second control input of said variable oscillator, wherein a digital loop is defined by the signal path along said second control signal from said digital frequency difference detector to said variable oscillator and along said oscillator output signal from said variable oscillator back to said digital frequency detector; wherein the bandwidth of said analog loop is greater than the bandwidth of said digital loop.