Wireless Terminal IQ Calibration for RF Gain Image Distortion
Find Innovative SolutionsGenerate Solutions
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 scheme (e.g., uplink 256 QAM) is used to increase data throughput, then productivity is improved, but image distortion becomes dominant and worsens signal quality
Solution Approach 1:
The patent changes the parameter of RF gain setting to three different levels (first, second, and third RF gain settings) to measure gain mismatches at multiple operating points. This allows the system to capture the RF gain dependent nature of image distortion and determine an accurate IQ mismatch coefficient that accounts for varying gain conditions, thereby reducing image distortion while maintaining high data throughput capability
Solution Approach 2:
The patent implements a feedback mechanism where the wireless terminal measures gain mismatches at different RF gain settings, estimates the IQ mismatch coefficient based on these measurements, and applies compensation adjustments to the I and Q paths. This closed-loop feedback approach continuously optimizes the signal to reduce image distortion, enabling the system to maintain high productivity (256 QAM) while correcting the harmful image distortion effect
2Measurement precision
If RF gain dependent image distortion is measured at multiple gain settings, then measurement precision is improved, but device complexity increases due to multiple measurements
Solution Approach 1:
The patent performs preliminary measurements of gain mismatches at three different RF gain settings during an initialization or calibration phase. These preliminary measurements are used to estimate the IQ mismatch coefficient before actual data transmission begins. By performing this complex measurement process in advance, the system achieves high measurement precision without adding complexity to the ongoing data transmission operation
Solution Approach 2:
The patent systematically varies the RF gain parameter across three distinct settings to measure gain mismatches at each level. This structured approach to parameter changes allows the system to capture the RF gain dependent behavior of image distortion. The measurements at multiple gain settings provide comprehensive data for estimating the IQ mismatch coefficient, improving measurement precision while keeping the process manageable through systematic parameter variation
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.