Patent attributes
The present invention provides an improved frequency doubling circuit, with adjustable phase offset. Briefly, rather than using the traditional equations cos (2ωt)=cos 2(ωt)−sin 2(ωt) and sin(2ωt)=2 sin(ωt)cos(ωt), the quadrature output signals are generated utilizing mixers, each having two input signals, separated in phase by the same offset. This minimizes the effects of the non-linearities introduced by the mixer, which therefore reduces amplitude mismatch between the quadrature signals. Also, the phase offset of the quadrature output signals can be tuned and calibrated using a phase shifting circuit. This phase shifting circuit realizes a tuning range of approximately 5° in programmable steps. This combination of circuits can be used to minimize the amplitude mismatch and phase errors, thereby reducing the amplitude of and interference caused by transmission of the image frequency to the receivers input.
