Power Amplifier Linearizer Using Reflective Hybrid Feedback
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Solution Overview
Problem
Existing power amplifiers face challenges in achieving good amplitude-to-amplitude (AM-AM) and amplitude-to-phase (AM-PM) metrics while maintaining high power added efficiency (PAE) and error vector magnitude (EVM) performance, often requiring complex digital pre-distortion and operating far from the 1 dB compression point, which degrades efficiency.
Innovation Solution
A linearization approach using a reflective hybrid coupler and non-linear termination circuit that pre-processes input signals to alter their AM-PM profiles, compensating for the non-linear distortion imposed by the amplifier, thereby improving the amplifier's linearity and extending its 1 dB compression point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital pre-distortion is used to improve linearity, then AM-AM and AM-PM metrics are improved, but device complexity and circuit requirements increase
Solution Approach 1:
The patent introduces a reflective hybrid coupler as an intermediary device that mediates between the input signal and the power amplifier. This coupler creates a feedback path that automatically adjusts the signal characteristics without requiring complex digital processing circuitry, thus improving linearity while avoiding the complexity penalty of digital pre-distortion systems
Solution Approach 2:
The system uses the power amplifier's own output signal as feedback through the reflective hybrid coupler. The amplifier's output is reflected back through the coupler to create a compensating signal that automatically corrects AM-AM and AM-PM distortion, eliminating the need for external complex control circuits or digital processors
2Manufacturing precision
If the amplifier operates far from the 1 dB compression point to improve linearity, then AM-AM and AM-PM metrics are improved, but power added efficiency degrades
Solution Approach 1:
The reflective hybrid coupler performs preliminary action by pre-adjusting the signal characteristics before they enter the power amplifier's non-linear region. The feedback mechanism anticipates and compensates for upcoming distortion, allowing the amplifier to operate closer to compression while maintaining linearity through the pre-applied correction
Solution Approach 2:
The system implements a feedback mechanism where the power amplifier's output is fed back through the reflective hybrid coupler to the input. This feedback loop continuously monitors and automatically corrects AM-AM and AM-PM distortion, enabling the amplifier to operate at higher power levels near compression while maintaining excellent linearity metrics
3Manufacturing precision
If high current density is used in FET fabrication to improve AM-AM and AM-PM metrics, then linearity is improved, but thermal performance and power efficiency worsen
Solution Approach 1:
The patent changes the operating parameters of the power amplifier by using the feedback mechanism to enable operation at lower current densities. The reflective hybrid coupler compensates for distortion that would normally require high current density operation, thus allowing the use of lower current density FETs that generate less heat and have better thermal performance
Data Source
AI summary
Circuits and methods for achieving good amplifier AM-AM and AM-PM metrics while achieving good power, PAE, linearity, and EVM performance. Embodiments compensate for a non-linear distortion profile (e.g., an AM-PM and/or AM-AM profile) in an amplifier by pre-processing an input signal, such as a radio-frequency signal, to alter the non-linear distortion profile of the input signal so as to compensate for the non-linear distortion profile imposed by a coupled device, such as an amplifier. An inventive aspect includes linearizing an output from an amplifier having a first non-linear distortion profile, including passing an input signal having a second non-linear distortion profile through a reflective hybrid coupler to a non-linear termination circuit, and reflecting a modified input signal from the non-linear termination circuit back through the reflective hybrid coupler as an output signal, the output signal having a third non-linear distortion profile shaped to compensate for the first non-linear distortion profile.