Broadband Power Amplifier Topology With Reduced Load Modulation
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Solution Overview
Problem
High-speed amplifiers constructed from semiconductor materials face challenges in meeting performance specifications for output power, signal linearity, signal gain, bandwidth, and efficiency, particularly due to load modulation effects that limit power handling and bandwidth capabilities in current Doherty amplifiers.
Innovation Solution
A multiclass power amplifier design with parallel amplification branches, including a main amplifier and secondary peaking amplifiers, where the secondary amplifiers are idle at low signal levels and become active as signal levels increase, with impedance inverters to maintain consistent impedance and reduce load modulation, allowing for improved efficiency and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional Doherty amplifiers are used, then power handling capability is limited, but bandwidth capabilities are also limited due to load modulation effects
Solution Approach 1:
The amplifier is divided into multiple parallel circuit branches (main amplifier branch and peaking amplifier branches), where each branch handles different signal levels. This segmentation allows the main amplifier to operate at low signal levels while peaking amplifiers activate at higher levels, reducing load modulation effects and improving both power handling and bandwidth capabilities simultaneously
2Power
If secondary amplifiers are added to increase power output, then device complexity increases, but the benefit is reduced load modulation and improved efficiency
Solution Approach 1:
Multiple peaking amplifiers are combined in parallel with the main amplifier, sharing common input and output nodes. This merging approach increases power output capability while maintaining a relatively compact structure, as the amplifiers share common circuit elements and can be integrated closely together
3Loss of energy
If impedance inverters are added to maintain consistent impedance, then device complexity increases, but load modulation is reduced and efficiency improves
Solution Approach 1:
Impedance inverters are introduced as intermediary components between the amplifiers and the combining node. These inverters transform impedances to maintain consistent load conditions for the amplifiers, reducing load modulation effects and improving efficiency without requiring complex control circuits
Data Source
AI summary
Low-load-modulation, broadband power amplifiers and method of use are described. The amplifiers can include multiple amplifiers connected in parallel to amplify a signal that has been divided into parallel circuit branches. One of the amplifiers can operate as a main amplifier in a first amplification class and the remaining amplifiers can operate as peaking amplifiers in a second amplification class. The main amplifier can see low modulation of its load between the fully-on and fully backed-off states of the amplifier. With lower load modulation, the power amplifiers described herein exhibit better power-handling capability and RF fractional bandwidth as compared to conventional amplifiers.