Distributed FET Power Amplifier Without Resistive Drain Termination
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Solution Overview
Problem
Wideband high power amplifiers (HPAs) face limitations in power added efficiency (PAE) and impedance matching issues due to reduced performance of their components compared to narrow band systems, and isolators may not be effective across wide bandwidths, affecting the amplification of radio frequency (RF) signals in radar and communication systems.
Innovation Solution
A distributed power amplifier design using two field effect transistors (FETs) with different peripheries and artificial transmission lines to minimize frequency limiting effects, operating at reduced drain voltage to achieve high PAE and impedance matching without resistive elements, allowing for wideband amplification across 2 to 18 GHz with performance comparable to narrow band amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolators are used to electrically isolate the HPA from the antenna, then the HPA's performance is protected from load pull, but over wide bandwidths the isolators are not available and the HPA's performance is pulled by the antenna's changing input impedance
Solution Approach 1:
The patent removes the isolator component from the system entirely, replacing it with a distributed amplifier architecture that inherently provides impedance isolation through its transmission line structure and multiple transistor configuration, thereby eliminating the bandwidth limitation imposed by isolators while maintaining HPA performance stability
Solution Approach 2:
The distributed amplifier structure serves multiple functions simultaneously: it provides signal amplification, impedance matching, and load isolation without requiring separate components, enabling wideband operation while protecting HPA performance across the entire frequency range
2Adaptability or versatility
If wideband amplifier designs are used, then wideband communication and radar systems can operate, but power added efficiency (PAE) is limited compared to narrow band systems
Solution Approach 1:
The patent divides the amplifier into multiple distributed transistor stages connected through transmission lines, with each stage contributing to the overall gain while maintaining high efficiency through optimized individual transistor operation and reduced parasitic effects across the wide bandwidth
Solution Approach 2:
The patent employs non-uniform transistor periphery distribution and optimized transmission line characteristics to maintain high PAE across the wide frequency range, adjusting the electrical parameters of each stage to compensate for frequency-dependent losses and maintain optimal operating conditions
3Adaptability or versatility
If wideband components are used in wideband systems, then wideband operation is achieved, but the electrical performance is typically less than that of narrow band systems
Solution Approach 1:
The patent uses asymmetric transistor sizing with different peripheries for transistors at different positions in the distributed chain, optimizing each transistor's contribution to the overall performance while compensating for position-dependent electrical characteristics, thereby achieving narrow-band-like performance across the wideband spectrum
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves high PAE and improved impedance matching across the wideband spectrum, enhancing the performance of wideband HPAs to match that of narrow band systems, with PAE ranging from 55% to 39% and input/output return losses better than 10 dB, while eliminating the need for resistive drain terminations that could degrade efficiency.
Implementation Method 1
a second gate terminal electrically coupled to the first gate terminal through a first inductor, a second drain terminal electrically coupled to the first drain terminal through a second inductor
Data Source
AI summary
A distributed power amplifier includes radio frequency (RF) input and output terminals. A first field effect transistor (FET) is coupled at a first gate terminal to the RF input terminal and at a first drain terminal to the RF output terminal. The first FET has a first periphery and a first source terminal electrically connected to ground potential. A second FET has a second periphery smaller than the first periphery. The second FET has a second gate terminal electrically coupled to the first gate terminal through a first inductor, a second drain terminal electrically coupled to the first drain terminal through a second inductor, and a second source terminal electrically connected to the ground potential. A drain voltage terminal, which excludes a resistive element, is electrically coupled to a drain bias network through which a drain bias voltage is applied to the first drain terminal and the second drain terminal.