Doherty Power Amplifier Load Control for Low-Power Efficiency
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Solution Overview
Problem
Existing power amplifier circuits, particularly load modulated balanced amplifiers (LMBA), face inefficiency at low input power due to high peak-to-average power ratio (PAPR) signals, which limits the ability to increase efficiency.
Innovation Solution
A power amplifier circuit configuration that includes a first power splitter, a Doherty amplifier circuit with a carrier amplifier and a peak amplifier, and a control amplifier to dynamically adjust load impedance, improving efficiency even at low input power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a load modulated balanced amplifier (LMBA) with class AB amplifiers is used, then the amplifier can operate with good linearity, but the efficiency is low at low input power
Solution Approach 1:
The amplifier is divided into two independent class AB amplifiers operating in parallel, each handling a portion of the signal. This segmentation allows each amplifier to operate efficiently at lower power levels while maintaining overall linearity through balanced operation, resolving the contradiction between linearity and efficiency at low input power.
Solution Approach 2:
The load impedance is dynamically controlled through a control amplifier that adjusts the impedance seen by the main amplifiers based on the signal level. This dynamic adaptation allows the amplifiers to maintain high efficiency across different input power levels while preserving linearity through active load modulation.
2Reliability
If the main amplifier operates in class AB, then the amplifier provides good linearity, but the efficiency cannot be increased for signals with high peak-to-average power ratio
Solution Approach 1:
A control amplifier dynamically adjusts the load impedance presented to the class AB main amplifiers based on the instantaneous signal level. This dynamic load modulation allows the amplifiers to operate at high efficiency across varying signal conditions while maintaining linearity through active impedance control, effectively resolving the efficiency limitation for high PAPR signals.
Solution Approach 2:
The control amplifier monitors the signal level and provides feedback control to adjust the load impedance in real-time. This feedback mechanism enables the system to adapt to high peak-to-average power ratio signals, maintaining both linearity and efficiency by optimizing the operating conditions based on the actual signal characteristics.
Data Source
AI summary
A power amplifier circuit includes: a first power splitter that splits an input signal into a first input signal and a second input signal; a Doherty amplifier circuit that includes a carrier amplifier and a peak amplifier and that amplifies the first input signal and outputs an output signal to an output terminal; and a control amplifier that amplifies the second input signal and outputs, to the Doherty amplifier circuit, a control signal for controlling load impedance of the Doherty amplifier circuit.