I/Q Calibration With Phase Stepper For QAM Transceivers
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Solution Overview
Problem
Existing QAM transmitters face challenges in accurately correcting amplitude and phase mismatches introduced by analog mixers, which can lead to incorrect signal interpretation by receivers and require calibration dependent on receiver section accuracy, often taking excessive time for calibration.
Innovation Solution
A self-calibrating QAM transceiver system that includes a signal generator, I/Q mismatch compensation module, and phase stepper module, allowing for independent calibration of transmitter section and reducing phase offset by varying the phase of reference I and Q signals based on amplitude and phase correction signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional I/Q mismatch calibration is performed using loopback switching and receiver section calibration, then I/Q mismatch can be compensated, but calibration time becomes excessive and receiver accuracy is required
Solution Approach 1:
The transmitter section performs self-calibration by injecting calibration signals through the analog mixers before signal transmission. This preliminary calibration action allows the transmitter to compensate for its own I/Q mismatch independently, without waiting for receiver-based calibration procedures to complete.
Solution Approach 2:
The transmitter section is enabled to calibrate itself using built-in calibration signal generators and detectors. The system uses self-generated calibration signals that pass through the analog mixers and are detected by the transmitter's own components, eliminating the need for external receiver section calibration and reducing overall calibration time.
2Measurement precision
If receiver section calibration is used for I/Q mismatch correction, then compensation can be achieved, but the process becomes dependent on receiver accuracy
Solution Approach 1:
The calibration process is segmented into independent transmitter section calibration and receiver section calibration. The transmitter performs its own self-calibration using injected calibration signals, while the receiver performs separate calibration. This segmentation allows each section to be calibrated independently without relying on the other's accuracy.
Solution Approach 2:
Calibration signals serve as intermediaries that allow the transmitter to measure and compensate for its own I/Q mismatch. These signals are injected through the analog mixers and processed through the transmitter's components, providing a mediator mechanism that enables independent transmitter calibration without requiring receiver section accuracy.
3Ease of manufacture
If analog mixers are used for I and Q signal conversion, then cost is reduced, but I/Q mismatch is introduced
Solution Approach 1:
The system applies preliminary anti-action by injecting calibration signals through the analog mixers before normal signal transmission. These calibration signals experience the same I/Q mismatch introduced by the analog mixers, allowing the transmitter to measure and compensate for the distortion in advance, thereby counteracting the harmful effect of the mixers' imperfections.
Solution Approach 2:
The transmitter uses feedback from detecting the calibration signals after they pass through the analog mixers to generate correction signals. These correction signals are then applied to compensate for the I/Q mismatch introduced by the mixers, creating a closed-loop feedback system that maintains signal accuracy despite the cost-effective use of analog components.
Data Source
AI summary
An I/Q calibration system for a quadrature amplitude modulation (QAM) mode transceiver includes a signal generator that generates reference in-phase (I) and quadrature (Q) signals. An I/Q mismatch compensation module generates compensated I and Q signals based on the reference I and Q signals and amplitude and phase correction signals. An I/Q mismatch calibration module generates the amplitude and phase correction signals. A phase stepper module varies a phase of the reference I and Q signals based on the amplitude and phase correction signals.