I-Q Imbalance Calibration via Closed-Form Solution
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Solution Overview
Problem
Existing calibration methods for in-phase and quadrature (I-Q) imbalance in RF receivers and transmitters are inefficient, requiring multiple processing passes and resulting in long processing times and inaccurate corrections, which can cause performance degradation and out-of-service interruptions in communication systems.
Innovation Solution
A closed-form solution is used to compute phase and gain adjustment constants directly from digitized I-Q samples, allowing for fast and accurate calibration of I-Q imbalances in both receivers and transmitters, either with a calibrated reference receiver or without, using test signals and digital processing to correct I-Q DC offset, phase, and gain errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iterative calibration approaches are used to correct I-Q imbalance, then calibration can be performed, but processing time becomes excessively long causing out-of-service interruptions
Solution Approach 1:
The patent replaces the iterative mechanical processing approach with a direct closed-form mathematical solution. Instead of repeatedly applying correction algorithms (iterative mechanical process), the invention uses explicit mathematical formulas to compute calibration constants in a single operation, substituting the iterative computational mechanism with a direct analytical solution that eliminates multiple processing passes.
Solution Approach 2:
The invention changes the fundamental parameter of calibration computation from iterative approximation to closed-form direct calculation. By transforming the calibration problem into a system of linear equations with explicit solutions, the patent changes the computational approach from repeated iterations to a single-pass calculation, fundamentally altering how calibration is performed to reduce processing time while maintaining accuracy.
2Productivity
If iterative calibration techniques are used, then calibration process can complete, but results become inaccurate and performance degrades
Solution Approach 1:
The patent substitutes the iterative computational mechanism with a direct closed-form mathematical solution. Instead of using repeated algorithmic passes that accumulate errors, the invention employs explicit mathematical formulas that directly compute the correct calibration constants in a single operation, replacing the iterative mechanical process with an analytical solution that guarantees accuracy.
Solution Approach 2:
The invention eliminates the need for feedback loops inherent in iterative methods by using a closed-form solution. The closed-form approach directly computes the correct calibration values without requiring repeated attempts or feedback corrections, thereby achieving both high speed and high precision simultaneously by removing the source of iterative inaccuracies.
3Manufacturing precision
If multiple processing passes are used for calibration, then corrections can be applied, but communication systems experience out-of-service interruptions
Solution Approach 1:
The patent replaces multiple iterative processing passes with a single closed-form calculation. This substitution reduces the calibration operation from a multi-step process that requires repeated iterations to a direct single-pass computation, thereby minimizing the duration of service interruption while maintaining the precision of I-Q balance correction.
Solution Approach 2:
The invention performs the complete calibration calculation in advance using closed-form formulas, computing all necessary correction constants before they are needed for actual communication operation. This preliminary action eliminates the need for repeated processing passes during service, reducing interruption time while ensuring accurate I-Q balance correction is ready for immediate application.
Data Source
AI summary
An embodiment of the present invention includes a technique to calibrate receiver and transmitter in a communication system. N digitized samples I(n) and Q(n) are stored. The N digitized samples represent in-phase and quadrature (I-Q) components, respectively, of a down-converted signal from a receiver. The I-Q components are generated from a quadrature demodulator or modulator having I-Q imbalance. Phase and gain adjustment constants are computed from the N digitized samples to compensate for the I-Q imbalance using a closed form solution.Another embodiment of the present invention includes a technique to calibrate a transceiver in a communication system without using a calibrated reference receiver. A first test signal at a first frequency is injected to a transmitter having a quadrature modulator with I-Q imbalance. The quadrature modulator has a carrier frequency. The transmitter generates a transmitter signal. The transmitter signal is detected to generate a composite signal having the first test signal and a second test signal at a second frequency twice the first frequency. The composite signal is digitized. I-Q direct current (DC) offset, phase, and gain corrections are computed from the digitized composite signal to correct the I-Q imbalance using a closed form solution.