Doherty Amplifier Peaking Stage Dual Drain Outputs
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Solution Overview
Problem
Current Doherty power amplifiers have inadequate bandwidth performance for future transmitter requirements, particularly in base-stations and broadcast applications, where wider RF bandwidths and high average efficiencies are needed, due to limitations in impedance inverters and parasitic impedances associated with packaged high-power PA devices.
Innovation Solution
The Doherty amplifier is enhanced by using a peaking amplifier with two drain outputs, where one drain output forms a wideband impedance inverter and the other connects directly to the RF load, along with a specialized layout and packaging that optimizes impedance inversion and load driving, eliminating the need for additional transformation networks, thereby increasing the relative bandwidth to over 45%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a classical two-way Doherty amplifier configuration is used, then the average efficiency is improved, but the bandwidth is limited to less than 10%
Solution Approach 1:
The peaking amplifier is divided into two separate drain outputs instead of a single combined output. This segmentation allows independent optimization of the impedance inverter function and the load driving function, enabling wideband operation while maintaining high efficiency. The first drain output connects to the output network for impedance inversion, while the second drain output connects directly to the RF load.
2Adaptability or versatility
If additional transformation networks are added to widen bandwidth, then the bandwidth is improved, but the device complexity increases
Solution Approach 1:
The specialized packaging with two drain outputs enables the peaking amplifier to perform multiple functions simultaneously. The first drain output handles the impedance inverter function across wide bandwidth, while the second drain output directly drives the RF load. This multi-functionality eliminates the need for additional transformation networks that would otherwise be required to achieve wideband operation.
Solution Approach 2:
The load driving function is extracted from the impedance inverter network by providing a separate direct connection from the second drain output to the RF load. This separation allows the impedance inverter to be optimized for wideband operation without being constrained by load matching requirements, eliminating the need for additional transformation networks.
3Ease of manufacture
If packaged high-power PA devices are used, then the manufacturing is simplified, but parasitic impedances limit the bandwidth performance
Solution Approach 1:
The packaging structure is specially designed with different connection qualities for different functions. The first drain output is optimized for the impedance inverter function with appropriate parasitic characteristics, while the second drain output is optimized for direct load driving with minimized parasitic impedances. This local quality differentiation allows the packaged device to achieve wideband performance despite the inherent parasitic limitations of packaging.
Data Source
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AI summary
A Doherty amplifier has at least one peaking amplifier which has first and second drain connections, wherein the first drain connection is connected to the output network, and the other second drain connection is connection to the load. By providing two drain connections, separate package leads to the peaking amplifier can be taken into account when designing the impedance inverter and an output impedance. In this way, the circuit operation can be optimised both for the impedance inversion function and for driving the output load.