Wireless Terminal IQ Mismatch Correction Across RF Gain Settings
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Solution Overview
Problem
In wireless terminals, RF gain dependent image distortion becomes a dominant factor with higher data throughput demands, particularly with uplink 256 quadrature amplitude modulation (QAM), as other distortions are suppressed, and existing technologies fail to effectively address this issue.
Innovation Solution
A method and circuit in a wireless terminal that measures gain mismatches in the I and Q paths at different RF gain settings, estimates an IQ mismatch coefficient, and applies adjustments to reduce image distortion by balancing the I and Q paths using variable resistors and calibration techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher modulation schemes (e.g., uplink 256 QAM) are used to increase data throughput, then productivity is improved, but image distortion becomes more significant and dominates signal quality
Solution Approach 1:
The patent applies parameter changes by measuring gain mismatches at multiple different RF gain settings and using these measurements to calculate correction coefficients. The digital baseband circuitry adjusts I and Q path parameters based on the calculated coefficients to compensate for image distortion, enabling higher order modulation schemes to operate reliably
Solution Approach 2:
The patent implements feedback by measuring the actual gain mismatches in the I and Q paths at different RF gain settings, using these measurements to calculate correction coefficients, and applying these coefficients to adjust the paths. This closed-loop feedback mechanism continuously compensates for image distortion, maintaining signal quality despite using higher throughput modulation schemes
2Reliability
If RF gain dependent image distortion is suppressed to maintain signal quality, then reliability is improved, but device complexity increases due to additional calibration requirements
Solution Approach 1:
The patent applies preliminary action by performing gain mismatch measurements and calculating correction coefficients in advance during factory calibration or initial device setup. These pre-calculated coefficients are stored and automatically applied during operation, eliminating the need for complex real-time calibration procedures while maintaining signal quality
Solution Approach 2:
The patent implements self-service by enabling the wireless terminal to automatically measure its own gain mismatches, calculate correction coefficients, and apply compensations without external intervention. The digital baseband circuitry performs all calibration functions autonomously, simplifying the overall system while maintaining reliability
Data Source
AI summary
A circuit in a wireless communications terminal/device and a method is described for reducing an image distortion. By measuring three gain mismatches of I path and Q path of a transceiver, and estimating a value of an IQ mismatch coefficient based on the three gain mismatches; and applying a measurement adjustment to the I path or the Q path based on the value of the IQ mismatch coefficient, the image distortion is reduced.