Method and apparatus to detect LO leakage and image rejection using a single transistor
LO leakage and Image are common and undesirable effects in typical transmitters. Typically, thirty complex hardware and algorithms are used to calibrate and reduce these two impairments. A single transistor that draws essentially no de current and occupies a very small area, is used to detect the LO leakage and Image Rejection signals. The single transistor operating as a square law device, is used to mix the signals at the input and output ports of the power amplifier (PA). The mixed signal generated by the single transistor enables the simultaneous calibration of the LO leakage and Image Rejection.
1. An apparatus to mix a first signal with a second signal comprising:
a plurality of circuit elements coupled in series forming a series signal path;
one of said plurality of circuit elements having an input node and an output node coupled within said series signal path;
a source of a transistor connected to said input node;
a gate of said transistor connected to said output node;
a drain of said transistor coupled to a resultant node, wherein
said transistor mixes said first signal at said input node with said second signal at said output node to generate a mixed signal between said first signal and said second signal at said resultant node, wherein said first signal comprises a first spectra comprising a first homodyne signal, a first LO leakage signal, and a first image rejection signal applied to said input node, and said second signal comprises 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 one of said circuit elements at said output 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.
2. The apparatus of claim 1 , further comprising:
an input port coupled to an input of said series signal path; and
an output port coupled to an output of said series signal path, wherein an up-converted RF signal is coupled to said input port.
3. The apparatus of claim 2 , further comprising:
an antecedent circuit element coupled to said one of said circuit elements at said input port;
and a subsequent circuit element coupled to said one of said circuit elements at said output port, wherein an up-converted RF signal is coupled to said antecedent circuit element.
4. The apparatus of claim 1 , wherein said one of said circuit elements is an amplifier stage that either non-inverts or inverts said second signal with regard to said first signal.
5. The apparatus of claim 1 , wherein said one of said circuit elements is an amplifier stage that amplifies and phase shifts said second signal with regard to said first signal.
6. 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.
7. The apparatus of claim 6 , further comprising:
an antecedent circuit element with an input port coupled to first circuit element at said input node; and
a subsequent circuit element coupled with an output port coupled to said first circuit element at said output node, wherein an up-converted RF signal is coupled to said input port.
8. The apparatus of claim 7 , further comprising: an antenna coupled to said output port.
9. The apparatus of claim 6 , wherein said first circuit element is an amplifier stage that either non-inverts or inverts said input signal at said output node.
10. The apparatus of claim 6 , wherein said first circuit element is an amplifier stage that amplifies and phase shifts said input signal at said output node.
11. 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.
12. The method of claim 11 , wherein said version components of said second spectra comprises at least a non-inverted or an inverted, an amplified or an attenuated, or a phase shifted component of said first spectra.
13. The method of claim 11 , further comprising coupling an up-converted RF signal is to said input port.
14. The method of claim 11 , wherein said first selected port corresponds to an input node or an output node of an amplifier, and said second selected port corresponds to a remaining node of said amplifier.