Joint Calibration of Transceiver IQ Mismatch Using Phase Shifted Loopback
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Solution Overview
Problem
Quadrature transceivers face challenges in accurately compensating for IQ mismatch (IQMM) in both transmit and receive paths, which can lead to performance degradation due to interference between mirror frequencies.
Innovation Solution
A method involving the use of loopback paths and phase shifters to send pilot signals through both transmit and receive paths, allowing for joint estimation of IQMM parameters by processing the received signals with algorithms such as block coordinate descent, and compensating for IQMM by adjusting coefficients of pre- and compensators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate calibration methods are used for transmit and receive paths, then each path can be calibrated independently, but the overall calibration accuracy deteriorates due to coupled IQMM effects
Solution Approach 1:
The patent merges the transmit and receive path calibration processes into a single joint calibration framework. By simultaneously estimating IQMM parameters for both paths using loopback signals with known phase shifts, the system resolves the coupling between transmit and receive calibration, achieving higher overall accuracy without requiring separate calibration procedures.
Solution Approach 2:
The patent introduces loopback signals with controlled phase shifts as intermediaries to enable joint calibration. These test signals traverse both transmit and receive paths, allowing the system to measure and estimate IQMM parameters for both paths simultaneously through the phase-shifted received signals.
2Measurement precision
If multiple pilot signals with different phase shifts are used, then joint estimation of TX and RX IQMM is enabled, but the signal processing complexity increases
Solution Approach 1:
The patent segments the calibration process into discrete steps: transmitting multiple pilot signals with different phase shifts, receiving and processing these signals, and then performing joint estimation. This segmentation allows complex IQMM parameters to be estimated systematically through structured processing rather than monolithic computation.
Solution Approach 2:
The patent changes the phase shift parameter of pilot signals to create distinguishable signal patterns. By varying phase shifts across multiple pilots and observing the corresponding changes in received signals, the system can isolate and estimate individual IQMM parameters (gain, phase, cross-terms) through controlled parameter variation.
Data Source
AI summary
A method of compensating for IQ mismatch (IQMM) in a transceiver may include sending first and second signals from a transmit path through a loopback path, using a phase shifter to introduce a phase shift in at least one of the first and second signals, to obtain first and second signals received by a receive path, using the first and second signals received by the receive path to obtain joint estimates of transmit and receive IQMM, at least in part, by estimating the phase shift, and compensating for IQMM using the estimates of IQMM. Using the first and second signals received by the receive path to obtain estimates of the IQMM may include processing the first and second signals received by the receive path as a function of one or more frequency-dependent IQMM parameters.