Quadrature Receiver Group Delay Equalization for Wideband I/Q Correction
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Solution Overview
Problem
Low-IF receivers face challenges in balancing amplitude and phase between in-phase and quadrature-phase signals due to unequal group delays, which are exacerbated by multiple RF bands being routed to the baseband, leading to reduced image rejection and band-limited phase imbalance correction.
Innovation Solution
A variable group delay equalizer is implemented to programmably delay either the I-channel or Q-channel, using a single-tap complex multiplier to correct frequency-independent mixer imbalances and produce a linear group delay mismatch versus frequency response, thereby counteracting non-linear mismatches caused by analog filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-step calibration and correction process is used to correct I/Q amplitude and phase imbalance, then phase imbalance correction is achieved near a single calibration frequency, but image rejection is reduced for wideband interferers due to the band-limited correction
Solution Approach 1:
The patent implements a dynamic phase correction approach where the phase correction amount is varied according to the frequency of the received signal. Instead of using a fixed phase correction value calibrated at a single frequency, the system continuously adjusts the phase correction based on the instantaneous frequency, thereby extending the effective correction bandwidth and improving image rejection for wideband interferers while maintaining correction accuracy
Solution Approach 2:
The patent changes the phase correction parameter dynamically based on frequency. By making the phase correction amount a function of frequency rather than a constant value, the system adapts to different frequency conditions and maintains effective image rejection across a wider bandwidth beyond the single calibration frequency point
2Adaptability or versatility
If seven RF bands are routed to the baseband portion of the receiver, then multi-band functionality is achieved, but I/Q group delay control becomes more difficult
Solution Approach 1:
The patent implements a universal phase correction mechanism that functions across multiple RF bands without requiring separate correction systems for each band. The frequency-dependent phase correction approach provides a unified solution that adapts to different frequency bands, maintaining I/Q group delay control effectiveness across the entire multi-band operating range while avoiding the need for complex band-specific correction circuits
3Ease of manufacture
If linear phase imbalance correction is used, then correction is simple to implement, but the correction does not vary with frequency and is limited to a region near a single calibration frequency
Solution Approach 1:
The patent transitions from a static linear phase correction to a dynamic frequency-dependent phase correction. The system automatically adjusts the phase correction amount based on the frequency of the input signal, providing adaptive correction that extends beyond the single calibration frequency region while maintaining implementation feasibility through systematic frequency tracking and adjustment
Data Source
AI summary
A device for minimizing group delay mismatch in a quadrature receiver (402) having an in-phase channel and a quadrature-phase channel. The device includes a microprocessor (465) for determining an I/Q phase imbalance between digital signals on an in-phase channel and digital signals on a quadrature-phase channel, and for calculating a group delay mismatch between the in-phase channel and the quadrature-phase channel, and a group delay equalizer (426). The group delay equalizer includes a delay line (505 and 605) for delaying one of the in-phase channel and the quadrature-phase channel by one of a plurality of delays, based on an amount of group delay mismatch.