Load-Modulated Power Amplifier Envelope Shaping for Phase Distortion
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Solution Overview
Problem
Existing RF power amplifiers suffer from phase and amplitude distortion due to impedance modulation, leading to inefficiencies and complexity in RF communication systems.
Innovation Solution
A load modulated power amplifier system with a controllable impedance modulated by a shaped envelope signal, utilizing an envelope shaping table with a smoothed response characteristic to compensate for phase distortion, and a power management circuit to control supply voltage, along with a gain shaping table to scale RF signals, achieving less than -120 dBm of phase and -130 dBm of amplitude distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If load impedance is modulated to improve power amplifier efficiency, then power efficiency is improved, but phase and amplitude distortion increases
Solution Approach 1:
The patent applies preliminary action by pre-shaping the envelope signal before it modulates the load impedance. The envelope shaping table pre-distorts the envelope signal in advance to compensate for the phase and amplitude distortion that will occur during impedance modulation, thereby maintaining signal fidelity while achieving high efficiency
Solution Approach 2:
The patent implements feedback by measuring the actual phase and amplitude distortion caused by impedance modulation and using this information to adjust the envelope shaping parameters. The system continuously monitors output distortion and modifies the pre-shaping characteristics to minimize distortion while maintaining efficiency
2Manufacturing precision
If envelope shaping is applied to reduce phase distortion, then phase distortion is reduced, but system complexity increases
Solution Approach 1:
The patent uses copying by implementing an envelope shaping table that stores pre-calculated shaping parameters for different operating conditions. Instead of performing complex real-time calculations, the system copies appropriate pre-computed envelope shapes from the table based on current power amplifier operating point, significantly reducing computational complexity while maintaining distortion compensation effectiveness
Solution Approach 2:
The patent applies segmentation by dividing the envelope shaping function into discrete segments corresponding to different power amplifier operating ranges. The envelope shaping table is segmented into multiple regions, each with optimized shaping characteristics for specific power levels, allowing the system to select appropriate segments rather than applying a single complex shaping function across all operating conditions
Data Source
AI summary
Envelope shaping tables calibrated for Isogain can provide a response characteristic that achieves a constant gain of the power amplifier. Although calibrating the load modulated power amplifier in this manner can provide low gain distortion (AM/AM), an Isogain calibration can result in phase distortion (AM/PM). To compensate for this phase distortion, in certain embodiments herein the envelope shaping table is smoothed at least at a lower end of the power range relative to an envelope shaping table calibrated for Isogain. By providing smoothing in this manner, spectral regrowth can be reduced.