I/Q Compensation Filters for Frequency-Dependent Image Rejection
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Solution Overview
Problem
Wireless transceivers face challenges in rejecting image signals due to phase and amplitude imbalances between in-phase and quadrature-phase signals, which affect signal quality and compliance with signal quality requirements such as image rejection ratio.
Innovation Solution
A method and system that compensate for frequency-dependent phase and amplitude imbalances by providing test tones to determine respective imbalances, calculating filter coefficients, and applying these coefficients to filters to correct for imbalances in received wireless signals, using a series of filters to ensure effective image rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple I/Q imbalance compensation is used, then device complexity is reduced, but image rejection ratio deteriorates due to frequency-dependent imbalances
Solution Approach 1:
The compensation filter is divided into multiple parallel filters, each handling a specific frequency range or imbalance component. This segmentation allows the system to address frequency-dependent imbalances effectively while keeping each individual filter relatively simple, thus resolving the contradiction between device complexity and image rejection ratio.
Solution Approach 2:
The filter coefficients are made dynamic and frequency-dependent rather than fixed. By adapting the filter characteristics to different frequencies, the system can compensate for frequency-dependent I/Q imbalances accurately without requiring excessive complexity in the overall compensation architecture.
2Reliability
If frequency-dependent compensation is implemented, then image rejection ratio is improved, but device complexity increases due to multiple filters and coefficient calculations
Solution Approach 1:
The plurality of filters is designed to handle multiple functions simultaneously - each filter processes specific frequency components while collectively they address the entire frequency spectrum. This multi-functionality allows effective frequency-dependent compensation without proportionally increasing overall system complexity.
Solution Approach 2:
The system changes filter parameters (coefficients) based on frequency to achieve frequency-dependent compensation. By dynamically adjusting parameters rather than using fixed complex structures, the system achieves high image rejection ratio with controlled complexity.
3Measurement precision
If multiple test tones are used for calibration, then measurement precision of imbalances is improved, but calibration time increases
Solution Approach 1:
The calibration process uses periodic test tones at different frequencies to measure I/Q imbalances. By using multiple discrete frequency points rather than continuous sweeping, the system achieves sufficient measurement precision for frequency-dependent characterization while limiting calibration time to practical levels.
Data Source
AI summary
Various embodiments are disclosed relating to a wireless transceiver. In an example embodiment, a method of compensating for phase imbalance and amplitude imbalance between corresponding in-phase signals and quadrature-phase signals includes providing a plurality of test tones of various frequencies to a receiver and determining, for each of the test tones, a respective phase imbalance and a respective amplitude imbalance between an in-phase (I) signal and a quadrature-phase (Q) signal of the test tone. The example method also includes determining a set of filter coefficients based on the determined phase and amplitude imbalances of the plurality of test tones and applying the set of filter coefficients to a plurality of filters. In the example method, a phase imbalance between an I signal and a Q signal of a received wireless signal is compensated for using a first filter of the plurality of filters. Further, an amplitude imbalance between the I and Q signals of the received wireless signal is compensated for using a second filter of the plurality of filters.