Method and apparatus to detect LO leakage and image rejection using a single transistor

An apparatus to generate a self-mixed signal comprising:

• a first circuit element including an input node and an output node;
• a source of a transistor coupled to said input node;
• a gate of said transistor coupled to said output node;
• a drain of said transistor coupled to a resultant node;
• a first spectra comprising a first homodyne signal, a first LO leakage signal, and a first image rejection signal applied to said input node;
• a version of said first spectra comprising a second homodyne signal, a second LO leakage signal, and a second image rejection signal modified by said circuit element and generated at said output node, wherein
• said transistor mixes said first spectra with said version of said first spectra, generating said self-mixed signal at said resultant node;
• a low pass filter (LPF) coupled to said resultant node;
• and
• a digital signal processor (DSP) coupled to said LPF, wherein said DSP calculates correction factors to reduce said LO leakage signals and said image rejection signals in all said spectra.

A method to generate a mixed signal between two selected ports comprising:

• coupling a plurality of circuit elements in series forming a series signal path, the series path comprising a plurality of ports, the plurality of ports comprising at least two of a set, the set comprising;
• a port between two adjacent circuit elements within said series signal path,
• an input port coupled to an input of a first circuit element in said series signal path, and
• an output port coupled to an output of a last circuit element in said series signal path;
• selecting any two of said plurality of ports;
• connecting a gate of a transistor to a first selected port of said two of said plurality of ports;
• connecting a source of said transistor to a second selected port of said two of said plurality of ports;
• and
• coupling a drain of said transistor to a resultant node, wherein
• said transistor mixes a signal at said first selected port with a signal at said second selected port, thereby
• generating at said resultant node said mixed signal between said two selected ports, wherein said signal at said first selected port has a first spectra comprising at least one of a homodyne signal, a LO leakage signal, and an image rejection signal applied to said input node;
• and said signal at said second selected port has a second spectra comprising at least one of a version of said homodyne signal, a version of said LO leakage signal, and a version of said image rejection signal modified by at least one of said plurality of circuit elements;
• coupling a low pass filter to said resultant node;
• and
• coupling a digital signal processor (DSP) to an output of said low pass filter to calculate correction factors to reduce said LO leakage signals and said image rejection signals of all signals within said series signal path.