AMPM Predistortion Calibration for RF Power Amplifier Linearity
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Solution Overview
Problem
Current RF power amplifiers in communication devices suffer from amplitude modulation to phase modulation (AMPM) distortion, leading to gain compression and decoding errors, necessitating predistortion to maintain signal linearity, which increases device complexity and calibration time.
Innovation Solution
A method to generate AMPM predistortion data by amplifying a test signal through the power amplifier, combining it with a reference oscillator signal via wave superposition, measuring the resultant interference, and determining a predistortion phase shift to maximize interference, thereby compensating for phase distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If predistortion circuitry is added to compensate for AMPM distortion, then signal linearity is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential AMPM distortion compensation functionality from a full predistortion system. By using a simple phase detector to measure phase distortion and a phase shifter to compensate for it, the invention implements minimal circuitry that addresses the core problem without the complexity of complete amplitude and phase predistortion systems.
Solution Approach 2:
The patent uses a copy of the modulated signal (fed back through a phase detector) to generate the compensation signal. This feedback copy allows the system to measure and correct phase distortion without requiring complex forward-path predistortion circuitry.
2Measurement precision
If calibration is performed on every device to obtain predistortion data, then compensation accuracy is improved, but calibration time increases
Solution Approach 1:
The patent employs a simple, low-cost calibration approach that can be quickly performed. The phase detector and phase shifter enable rapid measurement and correction of phase distortion without requiring lengthy calibration procedures or expensive measurement equipment, making per-device calibration practical and efficient.
3Use of energy by moving object
If power amplifier is operated at saturation to improve efficiency, then power efficiency is improved, but distortion increases
Solution Approach 1:
The patent applies preliminary phase correction through the phase shifter to counteract the phase distortion that will be generated when the power amplifier operates at saturation. By pre-adjusting the phase of the modulated signal based on feedback measurement, the system enables efficient saturated operation while maintaining signal integrity through compensating action.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces device complexity and calibration time by accurately determining predistortion data, improving signal linearity and reducing bit error rates and constellation skew.
Implementation Method 1
The amplified test signal is combined, by wave superposition, with a reference oscillator signal into a resultant signal. The resultant signal is an outcome of interference between the amplified test signal and the reference oscillator signal.
Data Source
AI summary
To generate amplitude modulation to phase modulation (AMPM) predistortion data that compensates for phase distortion in a power amplifier of a communication device, a test signal is amplified via the power amplifier. The amplified test signal is combined, by wave superposition, with a reference oscillator signal into a resultant signal. The resultant signal is an outcome of interference between the amplified test signal and the reference oscillator signal. The resultant signal power is measured using envelope information and, from the measurement, a predistortion phase shift is determined that when applied to the test signal maximizes the interference between the amplified test signal and the reference oscillator signal. AMPM predistortion data is generated to correspond with the predistortion phase shift.