Patent ID: 7130604

Claim:
A radio frequency (RF) demodulation circuit comprising: a first harmonic rejection mixing stage capable of receiving and mixing an incoming radio frequency (RF) signal having a frequency RF and a reference local oscillator (LO) signal having a frequency LO and generating therefrom a composite intermediate frequency (IF) signal having a frequency IF 1 ; a frequency divider for receiving said reference local oscillator signal and generating an in-phase local oscillator signal and a quadrature local oscillator signal both having a frequency LO/N; and a second harmonic rejection mixing stage for receiving said composite intermediate frequency (IF) signal having a frequency IF 1 and said in-phase local oscillator signal having a frequency LO/N and generating therefrom an in-phase output signal in which out-of-band harmonic signals are suppressed; wherein at least one of the first and second harmonic rejection mixing stages comprises: an RF signal input, an LO signal input, an IF signal output for providing the composite IF signal as differential outputs, and a plurality of signal transfer switches capable of connecting the RF signal input to the IF signal output and reversing a polarity of the differential outputs based on the frequency LO, the at least one of the first and second harmonic rejection mixing stages having a frequency response including nulls at one or more harmonics of the LO signal input.