Adaptive AM/PM Compensation for Polar PA Phase Error
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Solution Overview
Problem
Existing mobile terminals using polar modulation schemes face challenges in compensating for Amplitude Modulation to Phase Modulation (AM/PM) distortion due to varying Voltage Standing Wave Ratio (VSWR) and temperature conditions, which affect the spectral purity and Error Vector Magnitude (EVM) of the system.
Innovation Solution
A system and method for calibrating AM/PM compensation circuitry in mobile terminals, which includes seed look-up tables (LUTs) for ideal conditions and an adaptive LUT calibrated during transmit burst ramp-up, allowing for real-time compensation of phase errors across different frequency bands, sub-bands, and power settings, with optional seed LUT usage if strong interferers are detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If polar modulation scheme is used to improve power amplifier efficiency, then efficiency is greatly improved, but AM/PM distortion degrades spectral purity and EVM
Solution Approach 1:
The patent applies preliminary anti-action by pre-distorting the phase modulation component before it enters the power amplifier. The pre-distortion is calculated based on measured AM/PM characteristics, creating an equalizing curve that anticipates and counteracts the distortion that will occur during amplification. This preliminary correction prevents the harmful phase distortion from occurring in the first place, while maintaining the efficiency benefits of polar modulation.
2Ease of manufacture
If AM/PM pre-distortion is calibrated for ideal conditions, then calibration is simplified, but performance degrades under varying VSWR and temperature conditions
Solution Approach 1:
The patent implements dynamics by making the AM/PM pre-distortion adaptive rather than static. The system continuously monitors operating conditions including VSWR and temperature, and dynamically adjusts the pre-distortion parameters accordingly. This allows the system to maintain optimal performance across varying environmental and loading conditions, transforming a static calibration approach into a dynamic adaptation mechanism.
Solution Approach 2:
The patent employs feedback by measuring the actual phase error at the output of the power amplifier and using this information to adjust the pre-distortion parameters. The system creates a closed-loop control where the performance is continuously monitored and the pre-distortion is refined based on actual measurements, enabling the system to adapt to changing conditions while maintaining accurate compensation.
3Measurement precision
If adaptive calibration during ramp-up is implemented, then compensation accuracy is improved for current conditions, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by performing the adaptive calibration during the ramp-up period at the beginning of each transmit burst, before full power transmission begins. This timing allows the system to complete the measurement and adjustment process in advance, preparing the optimal pre-distortion parameters for the upcoming transmission. By doing the calibration work preliminarily during a natural transition period, the system achieves high accuracy without adding significant complexity to the main transmission path.
Data Source
AI summary
A system and method for calibrating Amplitude Modulation to Phase Modulation (AM/PM) compensation circuitry in a mobile terminal operating according to a polar modulation scheme are provided. In general, during ramp-up for a transmit burst, measurements of a phase error between an input and output of power amplifier circuitry in the transmit chain are obtained. Using the phase error measurements, the AM/PM compensation circuitry is calibrated and used to provide AM/PM compensation for the same transmit burst. By calibrating the AM/PM compensation circuitry using the phase error measurements obtained during ramp-up, the AM/PM compensation circuitry is calibrated for the desired frequency band, sub-band, and power control level setting as well as for the current load conditions at the antenna and ambient temperature.