RF Power Amplifier Linearization with Feed-Forward and Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current linearization techniques for RF power amplifiers, such as digital pre-distortion and Cartesian feedback, 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 I and Q error signals and injects them into an analog feedback loop, using digital error feed-forward to reduce open-loop distortion, thereby decreasing closed-loop distortion, and incorporates power supply modulation with an Ultra-Fast Tracking Power Supply (UFTPS) for efficient voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
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 Cartesian feedback
Solution Approach 1:
The linearization function is divided into two independent segments: digital pre-distortion processing and analog Cartesian feedback processing. The pre-distortion unit processes the input signal independently before the Cartesian feedback loop, allowing both techniques to operate simultaneously without interference. This segmentation enables each technique to address different aspects of distortion without requiring advance knowledge of power amplifier characteristics for the feedback portion.
Solution Approach 2:
An intermediate signal processing stage is introduced between the pre-distortion unit and the Cartesian feedback system. This intermediary stage conditions the pre-distorted signal to be compatible with the feedback loop requirements, enabling the combination of digital and analog processing techniques. The intermediary ensures that the pre-distorted signal maintains the necessary characteristics for effective feedback processing.
2Object-generated harmful factors
If pre-distortion is placed within the Cartesian feedback loop, then linearization is improved, but processing delay compromises the stability of the feedback system
Solution Approach 1:
The pre-distortion processing is performed in advance on the input signal before it enters the Cartesian feedback loop. By applying the inverse power amplifier characteristics to the input signal beforehand, the majority of distortion is corrected prior to feedback processing. This preliminary action reduces the burden on the feedback system and minimizes the required processing delay within the feedback loop, thereby maintaining stability.
3Use of energy by moving object
If Ultra-Fast Tracking Power Supply is used to increase amplifier efficiency, then power efficiency is improved, but significant additional distortion is introduced
Solution Approach 1:
The Cartesian feedback system is configured to specifically address the distortion introduced by the Ultra-Fast Tracking Power Supply. The feedback loop measures the actual output signal and compares it with the expected signal, generating error signals that are used to correct the UFTPS-induced distortion. This feedback mechanism enables the system to maintain high power efficiency while actively compensating for the additional distortion generated by the dynamic power supply modulation.
4Adaptability or versatility
If feedback linearisation is used without advance knowledge of power amplifier characteristics, then system flexibility is improved, but implementation cost increases
Solution Approach 1:
The system merges digital pre-distortion processing with analog Cartesian feedback processing into a unified linearization architecture. The digital pre-distortion unit provides initial correction based on known power amplifier characteristics, while the analog feedback system provides adaptive correction without requiring additional complex processing. This combination leverages the strengths of both approaches, maintaining system flexibility while reducing overall implementation complexity and cost compared to using feedback alone.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A power amplifier module and corresponding system are disclosed for linearising the output from a power amplifier. 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.