RF Power Amplifier Pre-Distortion Calibration Under PSD Limits
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Solution Overview
Problem
Existing digital pre-distortion calibration techniques for radio frequency power amplifiers in wireless devices violate regulatory power spectral density (PSD) limits when using high-power training signals, leading to reduced performance and increased current consumption.
Innovation Solution
A method to predict coefficients by incrementally transmitting narrowband or wideband training signals, performing curve fitting, interpolation, and extrapolation to determine a set of calibration coefficients that comply with PSD regulations, thereby enhancing power amplifier performance and reducing calibration time and current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-power training signals are used for digital pre-distortion calibration, then power amplifier performance is improved, but regulatory power spectral density limits are violated
Solution Approach 1:
The calibration process is divided into multiple segments: initial calibration at low power to establish baseline coefficients, followed by iterative refinement stages that progressively increase power levels while applying pre-distortion compensation. This segmentation allows the system to capture non-linear characteristics across the full power range without violating PSD limits at any single measurement point.
Solution Approach 2:
The system performs preliminary low-power calibration to establish initial pre-distortion coefficients before attempting high-power measurements. These preliminary coefficients are used to pre-compensate the training signal, enabling subsequent high-power calibration measurements to remain within regulatory PSD limits while still capturing the necessary non-linear behavior.
2Measurement precision
If high-power training signals are used for calibration, then calibration accuracy is improved, but current consumption increases
Solution Approach 1:
The calibration process uses periodic sweeping of the training signal through the power range, alternating between low-power measurement phases and brief high-power characterization phases. This periodic action allows the system to accumulate calibration data over multiple cycles, achieving high accuracy through integration of many low-power measurements with occasional high-power reference points, thereby reducing average current consumption.
3Object-affected harmful factors
If traditional calibration methods are used, then compliance with regulations is maintained, but power amplifier performance is reduced
Solution Approach 1:
The system implements a feedback loop where initial low-power calibration results are used to generate pre-distortion coefficients, which are then applied to subsequent high-power training signals. The system continuously monitors the effectiveness of the pre-distortion and iteratively refines the coefficients, ensuring that the final calibration achieves both regulatory compliance and optimal power amplifier performance through closed-loop optimization.
Data Source
AI summary
Methods and systems for improving digital pre-distortion calibration of a radio frequency power amplifier. The disclosed method includes, among other things, initiating digital pre-distortion calibration of a power amplifier of a radio frequency (RF) module, determining, based on a transmission power of a training signal transmitted to the power amplifier between a first transmission power value and a second transmission power value, a set of estimated coefficients, generating, based on a subset of the set of estimated coefficients, a set of predicted coefficients, wherein the set of predicted coefficients are derived from a fitting curve applied to the subset of the set of estimated coefficients, and storing the set of estimated coefficients and the set of predicted coefficients.