Method and apparatus for automatically balancing a radio-frequency mixer
AssigneeHewlett-Packard Company
InventorBruce A. Erickson
Life of this patent
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Abstract
An automatic balancing circuit for a radio frequency mixer which reduces LO-IF signal leakage, as well as minimizing second order harmonic distortion products is described. The circuit couples to in-phase and out-of-phase signal lines originating from the mixer, and comprises a differential gain network, a differential phase shift network and a combiner. The networks operate under the control of a microprocessor, which adjusts the networks so that the LO leakage signals, when combined, are almost completely eliminated.
Claims7
In a spectrum analyzer having a single balanced mixer with a balun for mixing a radio frequency input signal and a local oscillator input signal to produce an intermediate frequency signal, a circuit for minimizing leakage of the local oscillator signal into intermediate frequency circuitry, the circuit comprising:
- an in-phase signal line and an out-of-phase signal line, the lines being coupled to the balun, the lines carrying an in-phase and an out-of-phase signal, respectively;
- a differential gain network coupled to the in-phase and out-of-phase signal lines, the differential gain network adjusting the amplitude of the in-phase and out-of-phase signals;
- a differential phase shift network coupled to the differential gain network, the differential phase shift network receiving the amplitude adjusted in-phase and out-of-phase signals and shifting the signals in phase;
- a signal combiner coupled to differential phase shift network for combining the amplitude and phase adjusted in-phase and out-of-phase signals;
- and
- a microprocessor coupled to the differential gain network and the differential phase shift network for determining and controlling the amplitude and phase adjustments.
In a spectrum analyzer having a single balanced mixer with a balun for mixing a radio frequency in-put signal and a local oscillator input signal to produce an intermediate frequency signal, a circuit for minimizing leakage of the local oscillator signal into intermediate frequency circuitry, the circuit comprising:
- an in-phase signal line and an out-of-phase signal line, the lines being coupled to the balun, the lines carrying an in-phase and an out-of-phase signal, respectively;
- a differential gain network coupled to the in-phase and out-of-phase signal lines, the differential gain network adjusting the amplitude of the in-phase and out-of-phase signals;
- a differential phase shift network coupled to the differential gain network, the differential phase shift network receiving the amplitude adjusted in-phase and out-of-phase signals and shifting the signals in phase;
- a signal combiner coupled to the differential phase shift network for combining the amplitude and phase adjusted in-phase and out-of-phase signals;
- and
- a microprocessor coupled to the differential gain network and the differential phase shift network for determining and controlling the amplitude and phase adjustments,
- wherein the differential gain network comprises:
- a first and second field effect transistor, the gates of the transistors being respectively coupled to the in-phase and out-of-phase signal lines;
- a current sensing amplifier coupled to the drains of the transistors;
- and
- a digital-to-analog converter coupled to both the microprocessor and the gates of the transistors, and
- wherein the differential phase shift network comprises:
- a first and second varactor phase shifter coupled respectively to the drains of the first and second transistors;
- and
- a digital-to-analog converter coupled to the microprocessor and the first and second varactors.
An apparatus for minimizing local oscillator signal leakage and second order distortion products generated by a mixer, the mixer having an in-phase signal output and an out-of-phase signal output, the apparatus comprising:
- a microprocessor controlled phase shift network coupled to the in-phase signal output and the out-of-phase signal output for differentially adjusting the phase of the in-phase and out-of-phase signals;
- a microprocessor controlled gain network coupled to microprocessor controlled phase shift network for differentially adjusting the gain of the phase adjusted in-phase and out-of-phase signals;
- and
- a combiner coupled to the microprocessor controlled gain network for combining the gain and phase adjusted in-phase and out-of-phase signals.
An apparatus for minimizing local oscillator signal leakage and second order distortion products generated by a mixer, the mixer having an in-phase signal output and an out-of-phase signal output, the apparatus comprising:
- a microprocessor controlled phase shift network coupled to the in-phase signal output and the out-of-phase signal output for differentially adjusting the phase of the in-phase and out-of-phase signals;
- a microprocessor controlled gain network coupled to the microprocessor controlled phase shift network for differentially adjusting the gain of the phase adjusted in-phase and out-of-phase signals;
- and
- a combiner coupled to the microprocessor controlled gain network for combining the gain and phase adjusted in-phase and out-of-phase signals,
- wherein the microprocessor controlled gain network comprises:
- a first and second field effect transistor, the gates of the transistors being respectively coupled to the in-phase and out-of-phase signal outputs;
- a current sensing amplifier coupled to the drains of the transistors;
- and
- a digital-to-analog converter coupled to both the microprocessor and the gates of the transistors.
A method for minimizing leakage of local oscillator signal into intermediate frequency circuitry, the method comprising the steps of:
- generating an in-phase and an out-of-phase signal from a mixer combining a local oscillator signal and a radio frequency input signal;
- adjusting the amplitude of the in-phase and out-of-phase signals in a microprocessor controlled gain network;
- adjusting the phase of the in-phase and out-of-phase signals in a microprocessor controlled phase shift network;
- and
- combining the phase and amplitude adjusted in-phase and out-of-phase signals in a signal combiner.
Dependencies are inferred from the claim text.