Quadrature Receiver Image Rejection with Adaptive I/Q Compensation
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Solution Overview
Problem
Existing RF signal reception systems face challenges in reducing image frequency interference, which degrades signal quality and reduces channel information capacity due to noise and imprecision.
Innovation Solution
A digital or analog filter system that separates and compensates between desired and image signals using in-phase and quadrature mixer branches, phase rotation, and adders to form signals primarily based on desired and image components, with adaptive compensation to correct for channel mismatches and distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional filtering methods are used to reduce image frequency interference, then image rejection is improved, but signal loss and noise increase due to channel imperfections
Solution Approach 1:
The patent implements feedback by measuring the actual I and Q channel characteristics (gain and phase mismatches) and using these measurements to compute compensation coefficients. The compensation filter uses these coefficients to adjust the image signal, creating a closed-loop system that continuously corrects for channel imperfections and maintains high image rejection ratio.
Solution Approach 2:
The patent changes the parameters of the compensation filter dynamically based on measured channel conditions. By adjusting the filter coefficients according to actual I/Q channel mismatches, the system adapts to varying conditions and optimizes image rejection performance while maintaining signal quality.
2Measurement precision
If complex compensation filters are used to correct channel mismatches, then image rejection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent performs preliminary measurement of the I and Q channel characteristics during a calibration phase. These pre-measured parameters are stored and used to pre-compute compensation coefficients, eliminating the need for real-time complex calculations during signal processing and reducing operational complexity.
Solution Approach 2:
The patent creates a mathematical model (copy) of the channel imperfections based on measurements, and uses this model to design the compensation filter. Instead of directly combating complex physical mismatches, the system works with a simplified mathematical representation that captures the essential error characteristics.
3Object-affected harmful factors
If aggressive image rejection techniques are applied, then image frequency suppression is improved, but desired signal attenuation increases
Solution Approach 1:
The patent applies local quality by targeting the compensation specifically at the image frequency component while leaving the desired signal path unchanged. The compensation filter is designed to affect only the image signal path, applying correction locally where needed without impacting the overall desired signal integrity.
Data Source
AI summary
An RF receiver image rejection scheme. The RF is received and mixed in two quadrature channels allowing separation of the undesired image portion within the RF signal from the desired portion. The two channels can be summed to allow the image portions to cancel out and form a signal which is predominantly based on the desired portion. Another sum of the two channels can also be made to provide a signal which is primarily based on the image portion. Since there are some components of the image portion even in the compensated desired signal, that signal indicative of the image portion is used to compensate for that undesired portion.