I/Q Modulator Calibration Using Discrete Test Points
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Solution Overview
Problem
Analog I/Q modulators in transmitters face challenges with imperfect carrier rejection and sideband rejection due to gain, phase, and DC offset imperfections, requiring fast and costly analog-to-digital converters for calibration, which increases power consumption and complexity.
Innovation Solution
A transmitter with a calibration memory storing discrete test points and a compensator generates calibration carrier signals at a slower rate, using a low-performance analog-to-digital converter and iterative compensation values to reduce timing alignment requirements and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fast analog-to-digital converters are used for calibration, then measurement precision of feedback envelopes is improved, but power consumption and device complexity increase
Solution Approach 1:
The system performs preliminary calibration actions by storing discrete calibration test points in a calibration memory before actual calibration execution. This pre-computed approach allows the use of slower, lower-power analog-to-digital converters during calibration while maintaining measurement precision, as the calibration data is prepared in advance rather than requiring real-time high-speed conversion.
2Measurement precision
If fast analog-to-digital converters are used for calibration, then measurement precision of feedback envelopes is improved, but device complexity increases
Solution Approach 1:
Calibration test points are pre-computed and stored in calibration memory, eliminating the need for complex real-time calibration algorithms and high-speed conversion hardware. This preliminary preparation simplifies the overall device architecture while maintaining calibration accuracy.
Solution Approach 2:
The system uses stored calibration test points (copies of calibration data) instead of performing real-time calibration measurements. This copying approach replaces complex high-speed conversion hardware with simpler memory storage and retrieval operations, reducing device complexity while preserving measurement precision.
3Measurement precision
If continuous calibration tone is used, then calibration accuracy is improved, but timing alignment requirements and power consumption increase
Solution Approach 1:
The system uses periodic discrete calibration test points instead of continuous calibration tones. This periodic approach eliminates the need for continuous timing alignment between calibration signals and feedback envelopes, as each discrete test point is independently measured and stored, simplifying the timing requirements while maintaining calibration accuracy.
4Productivity
If multiple analog-to-digital converters are used, then calibration speed is improved, but cost and power consumption increase
Solution Approach 1:
Calibration test points are pre-computed and stored in memory, allowing a single low-speed, low-cost analog-to-digital converter to be used during calibration. This preliminary preparation eliminates the need for multiple high-speed converters, significantly reducing cost while maintaining calibration effectiveness through iterative compensation.
Data Source
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AI summary
A transmitter includes an input, a modulator, and a calibration memory configured to store discrete calibration test points. A compensator is coupled between the input and the modulator and cooperates with the calibration memory to cause the modulator to generate a respective calibration carrier signal for each of the discrete calibration test points during a calibration phase. A detector is coupled to an output of the modulator and is configured to determine respective calibration values of the calibration carrier signals during the calibration phase. A compensator calculator is coupled to an output of the detector, and is configured to generate compensation values for the compensator for use during an operation phase and based on the calibration values of the calibration carrier signals.