Power Amplifier AM/PM Predistortion via Burst Phase Shift Measurement
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Solution Overview
Problem
Existing methods for calibrating Amplitude Modulation to Phase Modulation (AM/PM) predistortion coefficients for power amplifiers in mobile terminals are inadequate as they do not account for changes in AM/PM distortion after the power amplifier is placed in the terminal, and they require specialized equipment for calibration.
Innovation Solution
A method involving a variable supply voltage controlled by an adjustable power control signal, which changes during a transmit burst to measure phase shifts and select appropriate predistortion coefficients for AM/PM compensation, allowing for calibration using existing test equipment and accounting for changes in power amplifier distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If predetermined AM/PM predistortion coefficients are used determined by manufacturer prior to placing power amplifier in mobile terminal, then manufacturing process is simplified, but the coefficients become inaccurate after power amplifier is placed in terminal due to changes in AM/PM distortion
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements during the manufacturing process using a test fixture. The calibration data is captured and stored before the power amplifier is installed in the mobile terminal, allowing the coefficients to be optimized for each specific device while maintaining manufacturing efficiency through automated measurement and data storage processes.
2Measurement precision
If calibration is performed after power amplifier is placed in mobile terminal, then predistortion coefficient accuracy is improved, but specialized test equipment is required and calibration process becomes complex
Solution Approach 1:
The patent introduces an intermediary test fixture that connects between the mobile terminal and external test equipment. This fixture provides a standardized interface and controlled measurement environment, simplifying the calibration process by eliminating the need for complex specialized equipment while enabling accurate post-installation calibration through a straightforward measurement setup.
3Ease of manufacture
If variable supply voltage is changed during transmit burst to measure phase shift, then calibration can be performed using existing test equipment, but the measurement process requires precise control of power control signals
Solution Approach 1:
The patent employs periodic action by changing the variable supply voltage at specific intervals during the transmit burst. The voltage transitions occur at predetermined times corresponding to known signal patterns, allowing the measurement system to capture phase shifts at controlled moments. This periodic modulation of the supply voltage enables systematic measurement while maintaining synchronization with the transmitted signal.
Data Source
AI summary
A method is provided for calibrating Amplitude Modulation to Phase Modulation (AM/PM) predistortion coefficients for a polynomial used to compensate for AM/PM distortion of a power amplifier in the transmit chain of a mobile terminal. In general, the power amplifier is controlled by a variable supply voltage, which is generated based on an adjustable power control signal. After the power amplifier is placed in the mobile terminal, a predetermined data pattern is transmitted in a transmit burst. During the transmit burst, the variable supply voltage is changed from a first value to a second value, and a resultant phase shift in the radio frequency output signal provided by the mobile terminal is measured. Based on the phase shift, one of numerous predetermined sets of AM/PM predistortion coefficients is selected as the AM/PM coefficients for the mobile terminal.