Reconfigurable Doherty Amplifier Biasing for Wideband Efficiency
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Solution Overview
Problem
Current microwave power amplifiers face challenges in achieving both broadband capabilities and high average efficiency, particularly in maintaining efficiency across a wide frequency range and reconfiguring the First Efficiency Peak (FEP) without the need for tunable circuit elements.
Innovation Solution
A power amplifier design comprising a main and auxiliary amplifier, where the main amplifier is biased by setting its drain-source bias equal to the auxiliary amplifier's bias times the main amplifier's output current ratio, and the impedances of the load and transmission line are set to be equal to the auxiliary amplifier's bias divided by the maximum current, making the input impedance independent of frequency below the First Efficiency Peak, thereby maintaining efficiency across a wide bandwidth without tunable elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If traditional Doherty amplifier designs are used, then high efficiency at peak power is achieved, but broadband capability and high average efficiency across wide frequency ranges cannot be maintained simultaneously
Solution Approach 1:
The patent implements dynamic bias control where the drain-source bias voltages of the main and auxiliary amplifiers are adjusted based on the instantaneous output power level. The main amplifier bias Vds,m and auxiliary amplifier bias Vds,a are modified from their traditional fixed values to dynamically adapt to different operating conditions, enabling the amplifier to maintain optimal efficiency across a wide bandwidth while supporting broadband operation.
Solution Approach 2:
The invention changes the traditional fixed bias parameters and impedance values to frequency-dependent and power-dependent parameters. By setting Vds,m equal to Vds,a times xb (where xb is the main amplifier output current ratio), and setting the load impedance ZL and transmission line impedance Zc to Vds,a/Imax,m, the amplifier achieves frequency-independent input impedance below the First Efficiency Peak, thereby enabling broadband operation with high average efficiency.
2Adaptability or versatility
If fixed bias and impedance values are used in Doherty amplifiers, then simple design is achieved, but reconfiguration of First Efficiency Peak and adaptation to different frequency bands require complex tunable circuit elements
Solution Approach 1:
The patent enables the amplifier to automatically adapt to different operating conditions through self-adjusting bias control. The drain-source bias voltages Vds,m and Vds,a are controlled to dynamically adjust based on the operating point without requiring external tunable circuit elements. This self-service mechanism allows reconfiguration of the First Efficiency Peak and adaptation to different frequency bands while maintaining simple circuit architecture.
3Reliability
If conventional Doherty amplifier biasing is used, then good Doherty characteristics are achieved, but frequency-dependent efficiency degradation occurs across bandwidth
Solution Approach 1:
The patent implements dynamic bias control where the drain-source bias voltages are adjusted in real-time based on the instantaneous output power and frequency. The main amplifier bias Vds,m and auxiliary amplifier bias Vds,a are modified from fixed values to dynamically adapt to different operating conditions, eliminating frequency-dependent efficiency degradation and maintaining consistent performance across the entire bandwidth.
Solution Approach 2:
The invention employs feedback mechanisms where the bias voltages are controlled based on the actual operating point and output characteristics. By monitoring the amplifier's performance and adjusting Vds,m and Vds,a accordingly, the system maintains optimal efficiency across frequency variations without requiring complex tunable elements.
Data Source
AI summary
The present disclosure provides a power amplifier comprising a main amplifier and an auxiliary amplifier. The power amplifier is configured to deliver an output power Pout. A First Efficiency Peak (FEP) is defined as a first efficiency peak in the power ratio Pout to Poutmax. Poutmax is a maximum power output of the power amplifier and PFEP defines a power ratio at the FEP. The main amplifier is configured to be biased by a main amplifier bias Vds,m that is substantially equal to an auxiliary amplifier bias Vds,a times xb with xb being a main amplifier output current in relation to the maximum current through the main amplifier when Pout equals PFEP. The impedances of a load and a main amplifier transmission line are arranged to be substantially equal. A corresponding method and a node in a wireless communication system comprising the power amplifier are also disclosed.