RF Power Amplifier Envelope Supply Predistortion for Linearity
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Solution Overview
Problem
RF power amplifiers in portable devices face challenges in meeting stringent linearity requirements while minimizing power consumption, especially when using amplitude-modulated or polar-modulated RF signals, due to inefficiencies in existing power supplies and gain modulation effects.
Innovation Solution
The implementation of a pre-distorted amplitude modulation (AM) power supply that receives and amplifies an AM signal to improve the linearity and efficiency of RF power amplifiers, allowing for reduced bandwidth usage and incorporating gain measurement and correction circuits to prevent clipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a constant power supply is used for the RF power amplifier, then the device complexity is reduced, but the linearity is degraded due to gain modulation by the RF envelope
Solution Approach 1:
The patent applies dynamics by transitioning from a constant power supply to a dynamic AM power supply that tracks the RF envelope. The power supply voltage is modulated according to the amplitude of the RF signal, allowing the amplifier to maintain constant gain and improve linearity while reducing distortion.
Solution Approach 2:
The patent changes the voltage parameter of the power supply dynamically. By modulating the power supply voltage in accordance with the RF envelope amplitude, the operating point of the amplifier is adjusted in real-time to compensate for gain compression and expansion, thereby improving linearity.
2Manufacturing precision
If the bandwidth of the AM power supply is increased to 12 megahertz or more for proper tracking, then the linearity is improved, but the efficiency is reduced due to the need for both switching and linear power supplies
Solution Approach 1:
The patent segments the power supply into multiple stages: a switching power supply for bulk voltage regulation and a linear power supply for fine bandwidth adjustment. This segmentation allows the switching supply to handle high-power operations efficiently while the linear supply provides the necessary bandwidth for linearity without consuming excessive power.
Solution Approach 2:
The patent applies partial action by using the linear power supply only for the bandwidth-critical portion of the signal, rather than applying it across the entire frequency range. This selective approach provides sufficient linearity improvement while minimizing the power consumption penalty associated with linear power supplies.
3Loss of energy
If an AM power supply is used to track the amplitude of the RF signal for maximum efficiency, then the power consumption is reduced, but the linearity is degraded due to gain expansion and compression
Solution Approach 1:
The patent implements feedback by monitoring the RF envelope amplitude and using this information to adjust the power supply voltage accordingly. The feedback mechanism ensures that the power supply tracking maintains the amplifier in its linear region, preventing gain compression and expansion while preserving efficiency benefits.
Solution Approach 2:
The patent applies preliminary action by pre-modulating the power supply voltage according to the expected RF envelope before the signal passes through the amplifier. This anticipatory adjustment ensures that the amplifier operates in its linear region throughout the signal cycle, preventing distortion before it occurs.
Data Source
AI summary
Embodiments of the present invention include amplitude-modulated or polar-modulated radio frequency (RF) power amplifier circuitry, in which an envelope power supply input to an RF power amplifier is powered by a pre-distorted amplitude modulation (AM) power supply. The pre-distorted AM power supply receives an AM signal, which is then pre-distorted and amplified to provide an AM power supply signal to the RF power amplifier. The pre-distortion of the AM signal is used to improve the linearity, the efficiency, or both, of the RF power amplifier. The pre-distortion provides a feed-forward system, which may allow use of a reduced bandwidth pre-distorted AM signal to an AM power supply and a reduced bandwidth AM power supply, which may increase efficiency.