Doherty Power Amplifier with Interdigitated Transistors
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Solution Overview
Problem
Doherty power amplifiers experience significant signal power loss at high frequencies due to the distributed nature of output bond pads, leading to poor power added efficiency, as the phase difference between signals at the edge fingers of amplifiers results in substantial signal power loss.
Innovation Solution
A Doherty power amplifier design with integrated and interdigitated power transistor fingers, phase shifters, and signal combiners, where the output combiner is closely electrically coupled to the peaking fingers, and a CLC topology is used to provide a 90-degree phase shift between carrier and peaking finger outputs, reducing phase discrepancies and signal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If more transistor fingers are used for higher-power amplifiers, then output power level is improved, but signal power loss increases due to distributed nature of output bond pads at high frequencies
Solution Approach 1:
The amplifier is divided into multiple independent amplifier units, each with its own transistor fingers and output bond pad. This segmentation allows each unit to operate independently with optimized local interconnections, reducing the cumulative phase discrepancy and signal loss that would occur in a single large amplifier with many fingers connected through long bond pads.
Solution Approach 2:
Multiple amplifier units are arranged in a spatial distribution across the package substrate, transitioning from a single-plane finger arrangement to a multi-dimensional layout. This allows output bond pads to be positioned closer to each amplifier unit, reducing the length and distributed effects of interconnections while maintaining high power output capability.
2Volume of moving object
If the wavelength of RF signal approaches the physical dimensions of transistor block, then amplifier size is reduced, but large phase difference results between signals at edge fingers leading to poor power added efficiency
Solution Approach 1:
By segmenting the amplifier into multiple small units, each unit maintains compact dimensions that are small compared to the RF wavelength, minimizing phase differences within each unit. The overall amplifier achieves high power output through the parallel combination of these compact units rather than through a single large transistor block.
Solution Approach 2:
The package substrate and output bond pads serve as intermediaries that collect and combine signals from multiple amplifier units. This intermediary structure allows signals from edge fingers to be combined with minimal phase discrepancy, maintaining power added efficiency while enabling a compact overall amplifier design.
Data Source
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AI summary
A multiple-path amplifier (e.g., a Doherty amplifier) includes first and second amplifier input terminals and an amplifier output terminal integrally-formed with a semiconductor die, and at least two amplifier cells positioned adjacent to each other between the amplifier input terminals and the amplifier output terminal. Each amplifier cell includes first and second transistors (e.g., field effect transistors) integrally-formed with the semiconductor die, where the first and second transistors each include a transistor input (e.g., a gate terminal) and a transistor output (e.g., a drain terminal). The first transistor input is coupled to the first amplifier input terminal, and the second transistor input is coupled to the second amplifier input terminal. A combining node is coupled to the second transistor output and to the amplifier output terminal, and a first phase shift element (e.g., an inductor) is electrically connected between the first transistor output and the combining node.