Patent ID: 6968017

Claim:
A frequency converter for shifting the frequency of an input signal by a desired frequency, the frequency converter comprising: (a) first oscillator means for producing a first signal at a first frequency and configured to receive an external reference frequency signal, the first signal derived with reference to the external reference frequency signal; (b) second oscillator means for producing a second signal at a second frequency also configured to receive the external reference frequency signal, the second signal derived with reference to the external reference frequency signal; (c) frequency conversion means for converting the frequency of the input signal equal to a frequency difference of the first signal and the second signal; and (d) mixing means for mixing said first signal and said second signal to produce a frequency difference signal representative of the frequency difference between the first and second signals; and (e) sampling means for sampling the frequency difference signal with a synthesized reference signal derived from the external reference signal such that aliasing results in an error signal corresponding to a frequency difference between the difference signal and a desired frequency shift, said the sampling means is configured to derive the synthesized reference signal from the external reference signal; (f) one of said first oscillator means and second oscillator means being responsive to the error signal to adjust the frequency of the first signal and second signal, respectively.