Push-Pull MOSFET RF Power Amplifier With Temperature-Stable Bias
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Solution Overview
Problem
High-power RF amplifiers operating over a range of 1-60 MHz typically rely on vacuum tubes, which is undesirable, and there is a need for amplifiers using a minimum number of MOSFET transistors instead.
Innovation Solution
A high-power RF amplifier design employing a push-pull configuration with multiple MOSFET transistors, each with an output power rating of at least 200 watts and operating with a drain-to-source voltage greater than 50 VDC, along with temperature compensating bias circuitry to maintain constant bias current over temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If vacuum tubes are used for high-power RF amplification, then power output and voltage handling are improved, but device complexity and reliability are worsened
Solution Approach 1:
The patent replaces vacuum tube technology with solid-state MOSFET transistors configured in a push-pull arrangement. This substitution eliminates the mechanical/vacuum-based vacuum tube system while achieving equivalent or superior power output through solid-state electronics, thereby reducing device complexity and improving reliability.
Solution Approach 2:
The patent divides the amplification function into multiple MOSFET transistors operating in a push-pull configuration, where each transistor handles a portion of the signal cycle. This segmentation allows the system to achieve high power output through coordinated operation of multiple lower-power components rather than requiring a single high-power vacuum tube.
2Device complexity
If MOSFET transistors are used instead of vacuum tubes, then device complexity is reduced, but temperature stability is worsened
Solution Approach 1:
The patent implements temperature compensating bias circuitry that uses feedback mechanisms to monitor and adjust the bias conditions of the MOSFET transistors based on temperature changes. This feedback system automatically compensates for temperature-induced variations in transistor characteristics, maintaining stable operation across temperature ranges.
Solution Approach 2:
The patent employs bias circuitry that dynamically adjusts electrical parameters (bias voltages and currents) in response to temperature changes. By changing these electrical parameters compensatorily, the system counteracts the effects of temperature on MOSFET performance, maintaining consistent amplification characteristics.
3Power
If multiple MOSFET transistors are used for high power output, then power rating is improved, but quantity of components increases
Solution Approach 1:
The patent merges multiple MOSFET transistors into a unified push-pull amplifier configuration where the transistors work together to deliver high power output. By combining the output stages of multiple transistors through a common output network, the system achieves high power rating while sharing common components such as the output transformer and biasing circuitry, thereby reducing the total component count compared to separate amplifier stages.
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 design achieves efficient power amplification with reduced component count and improved temperature stability, enabling reliable operation over a wide frequency range using MOSFET transistors instead of vacuum tubes.
Implementation Method 1
A broadband output transformer has a first balanced input connected to the first drain, and a second balanced input connected to the second drain. The broadband output transformer has an input to output impedance ratio of 1:4 and at least some flux cancellation occurs within the broadband output transformer.
Data Source
AI summary
An RF power amplifier includes a first amplifier module comprising a first push-pull amplifier including a first plurality of field effect transistors and a first output transformer. An output impedance of the first amplifier module is 25 ohms. A second amplifier module includes a second push-pull amplifier including a second plurality of field effect transistors and a second output transformer. An output impedance of the second amplifier module is 25 ohms. A combiner is connected to the first amplifier module and the second amplifier module. The combiner combines an output from the first amplifier module and an output from the second amplifier module into a combined signal. An output impedance of the combiner is 50 ohms.