IQ Gain Correction Loop for RF Receiver Quadrature Balance

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Radio receivers and transmitters face significant challenges in correcting IQ gain imbalance, particularly at high frequencies, leading to noise figure degradation and increased Bit-Error-Rate (BER) due to mismatched device characteristics, which existing technologies struggle to address effectively with minimal hardware requirements.

Innovation Solution

An IQ gain imbalance correction apparatus and method utilizing an error correction loop with a detector, loop filter, and multiplier to calculate and adjust the quadrature channel signal, minimizing hardware by calculating Error_detnew=|I′|−|Q′| and using Ki*Error_detnew to correct gain imbalance between in-phase and quadrature channels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If devices are used at high frequencies for quadrature demodulation, then radio frequency signal processing is enabled, but gain imbalance occurs due to inability to match device characteristics

Engineering Contradiction:

Improveradio frequency signal processing capabilityVSAvoidgain balance between channels

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by calculating and storing the ratio between in-phase and quadrature channel gains before actual signal processing. The system pre-determines the gain imbalance factor using calibration signals and stores this ratio for subsequent correction during normal operation, avoiding real-time complex adjustments

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter representation by working with the ratio of gains rather than absolute gain values. By defining a gain imbalance parameter (ratio between I and Q channel gains) and adjusting this parameter based on calibration measurements, the system corrects the gain imbalance without requiring precise matching of physical device characteristics at high frequencies

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If separate channels are used for in-phase and quadrature components, then quadrature demodulation is achieved, but different gain may be applied by respective channels causing gain imbalance

Engineering Contradiction:

Improvequadrature demodulation capabilityVSAvoidsignal accuracy due to gain imbalance

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent implements feedback by using the calculated gain ratio to continuously correct the quadrature channel signal. The system measures the actual gains of both channels, computes the ratio, and applies this ratio as a correction factor to the quadrature channel output, creating a closed-loop system that compensates for gain imbalance and improves signal accuracy

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces an intermediary element - the gain ratio calculation and correction unit - that mediates between the separate in-phase and quadrature channels. This intermediary computes the relationship between the two channels and applies appropriate scaling to the quadrature channel, enabling the separate channels to work together with matched gains without requiring direct physical matching of the channel components

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If minimal hardware is used for gain imbalance correction, then device complexity is reduced, but correction effectiveness may be compromised

Engineering Contradiction:

Improvehardware requirements for correctionVSAvoidgain imbalance correction accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent replaces mechanical/analog hardware solutions with digital signal processing. Instead of using complex analog circuitry to match and adjust gains at high frequencies, the system uses digital calculations to determine the gain ratio and applies digital multiplication to correct the quadrature channel, significantly reducing hardware complexity while maintaining correction accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent creates a digital model (copy) of the gain relationship between channels through calibration measurements. By measuring and storing the gain ratio as a digital parameter, the system can apply corrections through simple digital multiplication rather than requiring complex real-time analog adjustments, achieving accurate correction with minimal hardware

Inventive Principle:

Principle #26Copying

Data Source

PatentUS8085863B2Radio receiver or transmitter and method for reducing an IQ gain imbalance

Publication Date: 2011.12.27 WSOU INVESTMENTS LLC

AI summary

A radio receiver includes an in-phase channel and a quadrature channel, the channels being provided in parallel at a respective input with quadrature modulated radio frequency signals; and an error correction loop for detecting and correcting an imbalance in gain between at least part of the in-phase channel and a corresponding part of the quadrature channel, wherein the error correction loop comprises: a detector adapted to calculate Error_detnew=|I′|−|Q′|, where I′ and Q′ are the in-phase and quadrature channels respectively; a loop filter arranged to receive Error_detnew from the detector and calculate loop_filter_outnew+=Ki * Error_detnew, where Ki is the loop filter constant and loop_filter_outnew has an initial value of 1; and a multiplier arranged to receive loop_filter_outnew from the loop filter and adjust the signal of the quadrature channel by multiplying the signal by loop_filter_outnew.