Patent ID: 6127962
Filing Date: 2000-10-03
Classification: H03D

Abstract:
An image rejection mixer for down conversion of an incoming signal to a lower intermediate frequency signal, using the absolute difference of frequencies between the incoming signal and a local oscillator signal; wherein said image rejection mixer has a local oscillator whose local oscillator signal frequency f.sub.lo is chosen so as to provide an intermediate frequency signal at frequency f.sub.if for either of two incoming signals at frequencies f.sub.h and f.sub.l, respectively, wherebyf.sub.if =f.sub.h -f.sub.loandf.sub.if =f.sub.lo -f.sub.l ;wherein for signals at frequency f.sub.h, an image frequency signal exists at f.sub.l, as f.sub.l =f.sub.lo -f.sub.if ; andwherein for signals at frequency f.sub.l, an image frequency signal exists at f.sub.h, as f.sub.h =f.sub.lo +f.sub.if ;said image rejection mixer further comprising an input port at which either or both of said incoming signals at frequency f.sub.h and frequency f.sub.l are present, a controllable switch means, a control signal input port for said controllable switch means, a mixing element, a mixer local oscillator input port at which said local oscillator signal at frequency f.sub.lo is applied, and a mixer intermediate frequency output port from which said intermediate frequency signal at frequency f.sub.if is taken;said controllable switch means having two switch positions, and being capable of assuming either of a first switch position and a second switch position under the control of control signals applied to said control signal input port;said image rejection mixer arranged so that signals from said mixer local oscillator input port are applied to said mixing element, and so that intermediate frequency signals which are derived from said mixing element are applied to said mixer intermediate frequency output port;said mixing element being preceded by said controllable switch means having two positions so that, when said controllable switch means is in said first position thereof, a signal at frequency f.sub.h is fed from said mixer input port to said mixing element, and an image signal at frequency f.sub.l is rejected and decoupled from said mixing element; and when said controllable switch means is in said second position thereof, a signal at frequency f.sub.l is fed from said mixer input port to said mixing element, and an image signal at frequency f.sub.h is rejected and decoupled from said mixing element;said intermediate frequency signal at frequency f.sub.if comprising a downconverted signal representing either of said input signals at frequencies f.sub.h and f.sub.l, respectively, together with any noise which may occur at either of those same input signal frequencies; said intermediate frequency signal being substantially devoid of a downconverted signal representing the other of said input signals at frequencies f.sub.l and f.sub.h, respectively, together with any noise which may occur at that same image frequency.