Polar Transmitter Loopback Calibration for Rx-IQ Imbalance
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Solution Overview
Problem
Existing polar transceiver systems require external instruments for loopback-based Rx-IQ calibration, adding cost and complexity, while loopback operation is not feasible due to self-mixing issues with modulated clock phases.
Innovation Solution
A method using existing polar-Tx, IQ-Rx, and PLL blocks for loopback-based Rx-IQ calibration, employing AM modulation through a polar transmit power amplifier and unmodulated PLL DCO clocks to drive Rx-mixer signals, calculating a compensation parameter from looped-back signals to correct IQ imbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external instruments are used for Rx-IQ calibration, then calibration accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The transmitter performs self-calibration by looping its own transmitted signal back to the receiver. The system uses its internal components (transmitter, receiver, PLL) to calibrate the Rx-IQ imbalance without requiring external calibration instruments. The controller generates test signals, loops them back through the Tx/Rx switch, and processes the returned signals to compute compensation parameters.
Solution Approach 2:
The calibration process employs feedback by taking the transmitted signal, looping it back to the receiver, and using the returned signal to compute calibration parameters. The controller receives the looped-back signal, processes it through the receiver chain, and uses the output to calculate compensation parameters that correct the IQ imbalance.
2Ease of operation
If loopback operation is implemented with modulated clock phases, then calibration feasibility is improved, but self-mixing interference increases
Solution Approach 1:
The invention extracts the frequency modulation component from the test signal to eliminate self-mixing interference. By using AM modulation only (without FM) in the test signal generated during calibration, the system avoids the self-mixing problem that would occur with modulated clock phases. The test signal contains only amplitude information, allowing clean loopback operation.
Solution Approach 2:
The system changes the modulation parameters of the test signal during calibration by using AM modulation instead of FM or PM. This parameter change (removing frequency/phase modulation) eliminates the self-mixing interference while preserving the ability to perform accurate Rx-IQ calibration through loopback operation.
Data Source
AI summary
Polar transmitter calibration Various embodiments relate to a transmit and receive system using polar modulation, including: a transmitter configured to produce a transmit signal using modulation; a receiver configured to receive a transmit signal using in-phase/quadrature (IQ) processing; a Tx/Rx switch configured to loop a transmitted signal from the transmitter back to the receiver for calibration; and a controller configured to: command the transmitter to generate a real signal; command the Tx/Rx switch to loop the real signal back to the receiver to produce a first received signal; command the transmitter to generate an imaginary signal; command the Tx/Rx switch to loop the imaginary signal back to the receiver to produce a second received signal; determine a compensation parameter based on the first received signal and the second received signal; and command the receiver to compensate a third received signal based upon the compensation parameter.