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, leading to degraded transmitter performance, and existing calibration methods require fast and costly analog-to-digital converters for precise timing alignment and high-speed calibration.
Innovation Solution
A transmitter with a calibration memory storing discrete test points generates calibration carrier signals for each test point, allowing for slower calibration and using a low-performance analog-to-digital converter, eliminating the need for continuous tones and precise timing alignment, and iteratively calculating compensation values for the compensator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous calibration tone is used with fast analog-to-digital converter, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts only the essential calibration information by using discrete calibration test points instead of continuous tones. The calibration is performed at specific discrete moments rather than continuously, removing the need for high-speed continuous sampling while still obtaining sufficient calibration data for gain, phase, and DC offset compensation.
Solution Approach 2:
The calibration process uses periodic discrete test points rather than continuous calibration tones. By applying calibration signals at specific periodic intervals with discrete test points, the system achieves necessary measurement precision without requiring fast analog-to-digital converters that would be needed for continuous high-rate sampling.
2Measurement precision
If continuous calibration tone is used, then calibration accuracy is improved, but power consumption increases
Solution Approach 1:
The calibration process uses periodic discrete test points rather than continuous calibration tones. By applying calibration signals at specific periodic intervals with discrete test points, the system achieves necessary measurement precision without requiring continuous high-power signal generation and processing, thereby reducing overall power consumption.
Solution Approach 2:
The patent applies partial action by using only discrete calibration test points at specific moments rather than continuous calibration tones. This partial calibration approach provides sufficient accuracy for compensation while consuming significantly less power than continuous calibration methods.
3Productivity
If fast feedback loop is used for calibration, then calibration speed is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts only the essential calibration information needed at discrete moments rather than requiring continuous fast feedback. By taking out only the critical calibration parameters at specific test points, the system achieves adequate calibration speed without complex fast feedback loops.
Data Source
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.