Digital I/Q Mismatch Compensation in Low IF Receivers
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Solution Overview
Problem
Conventional low intermediate frequency receivers face interference due to I/Q mismatch, with existing compensation methods either requiring symmetric signals or being less accurate and more costly due to reliance on analog multipliers, especially when polyphase filters are used.
Innovation Solution
A receiver system that includes an analog down-conversion unit, a digital down-conversion unit, and a compensation unit with a time domain-frequency domain transforming module, compensation parameter calculating module, and compensation module to digitally compensate for I/Q mismatch by transforming and processing baseband signals in both time and frequency domains, allowing for asymmetric signal handling and reduced design costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital compensation methods (DIRP or complex multiplier) are used to compensate I/Q mismatch, then measurement precision is improved, but device complexity increases and adaptability decreases because symmetric signal characteristics are required
Solution Approach 1:
The patent applies asymmetry by removing the symmetric signal requirement from digital compensation methods. The compensation unit processes I and Q baseband signals independently through separate filtering and delay paths, allowing asymmetric signal characteristics to pass through without requiring symmetric properties. This enables compatibility with polyphase filter schemes that produce asymmetric output signals.
Solution Approach 2:
The patent segments the compensation process into distinct functional blocks: a compensation parameter calculating module that determines correction parameters, and a compensation module that applies these parameters through separate processing paths for I and Q signals. This segmentation allows independent optimization of each path without requiring overall signal symmetry.
2Ease of operation
If analog multiplier is used for I/Q mismatch compensation, then ease of operation is improved, but manufacturing precision deteriorates due to inferior analog multiplier accuracy
Solution Approach 1:
The patent substitutes the mechanical/analog multiplier system with a digital compensation system. The compensation parameter calculating module computes correction parameters digitally, and the compensation module applies these parameters through digital signal processing operations. This replacement maintains ease of operation through programmable control while achieving superior manufacturing precision through accurate digital computation.
3Productivity
If polyphase filter is used for down-conversion, then productivity is improved by reducing bit numbers for ADC, but object-generated harmful factors increase due to I/Q mismatch interference
Solution Approach 1:
The patent converts the harmful I/Q mismatch interference into a correctable distortion by introducing a compensation unit that calculates and applies correction parameters. The compensation parameter calculating module analyzes the distorted signals and generates correction factors that, when applied by the compensation module, eliminate the interference and recover the target signal from the polyphase filter output.
Data Source
AI summary
A receiver for compensating I/Q mismatch includes an analog down-conversion unit for receiving a radio frequency signal and down-converting the RF signal into a set of digital low intermediate frequency (IF) signals, a digital down-conversion unit receiving the set of digital low IF signals and down-converting the set of digital low IF signals into first and second baseband signals, and a compensation unit. The compensation unit receives the first and second baseband signals, calculates a compensation parameter based thereon, and compensates I/Q mismatch effect according to the first and second baseband signals and the compensation parameter so as to output a target signal.