Two-Filter IQ Mismatch Correction for Zero-IF and Low-IF Chains
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Solution Overview
Problem
In wireless infrastructure, zero-IF and low-intermediate frequency architectures face IQ mismatch errors due to gain/phase and delay mismatches in analog signal chains, leading to side-band leakage, which existing correction methods using filters struggle to fully address.
Innovation Solution
A two-filter architecture is employed in the digital signal chain for IQ mismatch correction, featuring an in-path and a cross-path filter element, along with corresponding delay elements, to filter In-phase and Quadrature digital signals, effectively compensating for IQ mismatch impairments introduced by the analog chain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional filter-based IQ mismatch correction is used, then some correction is achieved, but the correction is insufficient and side-band leakage remains
Solution Approach 1:
The correction architecture is segmented into four distinct filter paths: I-path filter, Q-path filter, cross-path filter, and I-Q mismatch estimator. Each segment handles specific aspects of the mismatch correction, allowing independent optimization and more precise correction of different mismatch components.
Solution Approach 2:
An I-Q mismatch estimator is introduced as an intermediary component that measures the actual mismatch conditions and provides feedback to the filter elements. This mediator enables adaptive adjustment of filter coefficients to achieve more accurate correction.
2Measurement precision
If complex correction architectures are used to reduce IQ mismatch errors, then correction accuracy improves, but device complexity increases
Solution Approach 1:
The filter elements are designed to perform multiple functions: I-path and Q-path filters handle direct path corrections, while cross-path filters handle coupling between I and Q channels. This multi-functionality reduces the need for separate dedicated circuits for each correction task.
Solution Approach 2:
The architecture merges the mismatch estimation function with the correction filter structure, allowing the system to adaptively adjust filter coefficients based on real-time mismatch measurements. This integration reduces overall system complexity compared to having separate estimation and correction systems.
Data Source
AI summary
IQ mismatch correction for analog chain IQ mismatch impairments is based on a two-filter architecture. In either RX or TX, an IQmc mismatch corrector (digital chain) filters I and Q digital signals, and includes an I-path to receive the I signal, and a Q-path to receive the Q signal, and is configured with two filters: an in-path filter to filter either the I signal or the Q signal received in the same path; and a cross-path filter to filter either the I signal or the Q signal received in the other path. The IQmc mismatch corrector can include: an I-path delay element to provide a delay to the I signal corresponding to a delay through either the in-path filter or the cross-path filter; and a Q-path delay element to provide a delay to the Q signal corresponding to a delay through either the in-path filter or the cross-path filter.