RF Power Amplifier Linearization With Feedback and Pre-Distortion
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Solution Overview
Problem
Current linearization techniques for RF power amplifiers, such as digital pre-distortion and feedback methods, are not sufficient to address the distortion introduced by Ultra-Fast Tracking Power Supply (UFTPS) systems, which increase efficiency but add significant distortion, and are not compatible for simultaneous application.
Innovation Solution
A combined pre-distortion and feedback compensation system that generates estimated error signals and injects them into an analog feedback loop, using digital error feed-forward to reduce open-loop distortion, and incorporates Ultra-Fast Tracking Power Supply (UFTPS) for variable supply voltage, allowing for simultaneous benefits of both linearization mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital pre-distortion is used to linearize the power amplifier, then distortion is reduced, but the system requires advance knowledge of power amplifier characteristics and cannot be combined with feedback systems
Solution Approach 1:
The patent segments the linearization function into two parts: a feed-forward path that applies pre-distortion based on stored amplifier characteristics, and a feedback path that measures actual output and corrects errors. This segmentation allows both techniques to operate simultaneously without conflict, as each handles different aspects of distortion correction.
Solution Approach 2:
The patent introduces an intermediary feedback path that measures the actual power amplifier output and generates correction signals. This intermediary mechanism bridges the gap between the pre-distorted input signal and the actual output, allowing the system to compensate for uncertainties and variations that pre-distortion alone cannot address.
2Adaptability or versatility
If feedback linearization is used to correct power amplifier distortion, then no advance knowledge of characteristics is required, but the system becomes more complex and costly to implement
Solution Approach 1:
The patent merges the simplicity of pre-distortion (which uses stored characteristics to correct most distortion) with the adaptability of feedback (which measures and corrects remaining errors). By combining these approaches, the system achieves high linearization accuracy without requiring a complex feedback-only implementation.
Solution Approach 2:
The patent applies preliminary pre-distortion correction to the input signal before amplification, based on stored power amplifier characteristics. This preliminary action removes the majority of expected distortion, reducing the burden on the feedback path and allowing for a simpler, less costly feedback implementation.
3Use of energy by moving object
If Ultra-Fast Tracking Power Supply is used to increase power amplifier efficiency, then power consumption is reduced, but significant distortion is introduced
Solution Approach 1:
The patent uses feedback to measure the distortion introduced by the UFTPS and generate correction signals that compensate for these variations. The feedback path continuously monitors the power amplifier output and adjusts the correction signals to counteract the distortion caused by dynamic supply voltage changes.
Solution Approach 2:
The patent introduces an intermediary feedback measurement path that specifically captures the distortion introduced by the UFTPS. This intermediary mechanism allows the system to separately identify and correct supply-voltage-induced distortion without affecting the efficiency benefits of the UFTPS.
Data Source
AI summary
A power amplifier module and corresponding system for linearizing the output from a power amplifier includes both a feedback system, containing a compensator and the power amplifier in a feedback loop, and a pre-distortion compensation system injecting pre-distortion signals into or before the feedback system are used to compensate for non-linearities in the overall system. The pre-distortion signals may be mixed with signals from the compensator or may be filtered to take into account the loop compensator transfer function of the feedback loop, mixed with baseband signals and then converted into analog signals that are provided to the feedback loop. In modules containing a tracking power supply, an envelope calculator calculates an RF envelope of the baseband signals, which the pre-distortion system uses in conjunction with the baseband signals to generate the pre-distortion signals mixed with the signals from the compensator.