I/Q Mismatch Calibration in Direct Conversion Receivers
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Solution Overview
Problem
Direct conversion radio frequency receivers face challenges in correcting I/Q mismatch due to gain and phase errors, which are difficult to calibrate using existing methods.
Innovation Solution
A system and method that calibrate I/Q mismatch in direct conversion receivers using a random signal with a two-dimensional I versus Q trajectory, computing variance and covariance of the in-phase and quadrature components to determine a correction matrix for gain and phase mismatch errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If baseband correction is performed using a distortion matrix, then I/Q mismatch correction is achieved, but the distortion matrix is difficult to measure and calibrate
Solution Approach 1:
The patent introduces RF noise as an intermediary signal to measure the distortion matrix. Instead of directly measuring the complex distortion matrix, the system uses RF noise as a mediator that passes through the receiver chain, allowing the distortion matrix to be calculated from the statistical properties (variance and covariance) of the noise signal at different points in the system.
Solution Approach 2:
The patent replaces traditional calibration methods with statistical signal processing. Instead of using mechanical or electronic calibration procedures to directly measure gain and phase errors, the system substitutes these with computational methods that calculate the distortion matrix from the statistical characteristics (variance and covariance) of RF noise samples.
2Reliability
If gain and phase errors are corrected in the receiver, then I/Q mismatch is reduced, but the calibration process becomes complex
Solution Approach 1:
The patent changes the approach from directly measuring and correcting gain and phase parameters to measuring statistical parameters (variance and covariance) of RF noise and deriving the distortion matrix from these. This parameter transformation simplifies the calibration process by working with statistical moments rather than direct electrical measurements.
Solution Approach 2:
The system performs self-calibration by using the RF noise already present in the receiver environment. The calibration process utilizes the receiver's own noise floor and internal signal paths, eliminating the need for external calibration equipment or additional hardware components.
Data Source
AI summary
A system and method are provided for calibrating for an I/Q mismatch of a direct conversion receiver based on a random signal having a two-dimensional I versus Q trajectory, such as radio frequency (RF) noise. In general, the random signal is received and downconverted to a quadrature baseband signal having an in-phase component and a quadrature component. The variance of the in-phase component, the variance of the quadrature component, and the covariance of the in-phase component with the quadrature component are computed based on samples of the quadrature baseband signal. A correction matrix used to compensate for the I/Q mismatch of the receiver and/or I/Q mismatch including a gain mismatch and a phase mismatch of the receiver is then computed based on the variance of the in-phase component, the variance of the quadrature component, and the covariance of the in-phase component with the quadrature component.