Multi-Stage Doherty Amplifier Asymmetric Driver Gain
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Solution Overview
Problem
Existing RF power amplifiers face a trade-off between efficiency and linearity, with Doherty amplifiers not achieving sufficient efficiency while maintaining desirable system linearity, particularly due to power gain degradation and inefficiencies in the driver stage.
Innovation Solution
A multi-stage Doherty amplifier design with a main and auxiliary amplifier circuit, featuring a higher power rating for the driving stage of the auxiliary amplifier, asymmetric input signal splitting, and periphery scaling between the main and auxiliary amplifier stages, along with controlled turn-on characteristics through bias voltage combinations, to enhance overall system efficiency without significant linearity degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a Doherty amplifier is used to improve efficiency, then energy efficiency is improved, but power gain is degraded
Solution Approach 1:
The amplifier is divided into multiple stages: a first amplification stage (Class AB) and a second amplification stage (Doherty configuration). This segmentation allows the signal to be progressively amplified, with the first stage providing initial gain and the second stage providing additional gain while maintaining efficiency through Doherty operation. The multi-stage approach distributes the amplification function across different configurations to balance gain and efficiency requirements.
Solution Approach 2:
The Doherty amplifier employs asymmetric operation where a main amplifier operates continuously and an auxiliary amplifier is activated only when needed (when the main amplifier approaches saturation). This asymmetric activation pattern allows the system to maintain high efficiency during normal operation while providing additional power gain when required, resolving the contradiction between efficiency and power gain.
2Use of energy by moving object
If the driver stage power rating is reduced to improve efficiency, then energy efficiency is improved, but the ability to provide sufficient gain is degraded
Solution Approach 1:
The driver stage is segmented into two amplification stages rather than using a single large amplifier. The first stage (Class AB) handles lower power levels efficiently, and the second stage (Doherty) provides additional gain capability when needed. This segmentation allows the driver stage to maintain high efficiency at normal operating levels while retaining the capability to provide sufficient total gain through the combined stages.
Solution Approach 2:
The first amplification stage performs preliminary amplification of the input signal before it enters the second Doherty stage. This preliminary action reduces the burden on the second stage, allowing it to operate more efficiently while still achieving the required total gain. The signal is pre-conditioned and partially amplified before the efficiency-critical Doherty stage processes it.
Data Source
AI summary
An amplifier has a main amplifier circuit with multiple amplification stages, including a driving stage and an auxiliary amplifier circuit with multiple amplification stages, including a driving stage. A splitter circuit splits an input signal to provide path asymmetry in splitting the input signal between the main amplifier path and auxiliary amplifier path. The driving stage of the auxiliary amplifier circuit has a power rating higher than the power rating of the driving stage of the main amplifier circuit to provide a gain asymmetry in the amplifier circuit paths.