Cascaded FET Power Amplifier Gain Control Under Uneven Heating
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Solution Overview
Problem
In satellite news gathering systems, cascaded solid-state power amplifiers using gallium arsenide FETs experience uneven temperature distribution and gain variation due to temperature changes, which cannot be effectively compensated by single-point temperature sensing, leading to instability in signal amplification.
Innovation Solution
A power amplifier design with multiple temperature sensors positioned at different stages of the cascaded FETs and a control circuit that adjusts the variable attenuator to compensate for gain variations by calculating and controlling the temperature changes at each stage, ensuring stable gain across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple FETs are cascaded to achieve high gain (60 dB), then the gain is sufficient for SNG system requirements, but the temperature distribution becomes uneven and gain variation increases
Solution Approach 1:
The patent divides the temperature monitoring function into multiple segments by placing temperature sensors at different positions within the amplifier circuit. Specifically, temperature sensors are arranged in the vicinity of both the main amplifier circuit and the distortion signal amplifier circuit, allowing independent temperature detection and compensation for each segment. This segmentation enables precise temperature compensation for each FET stage, resolving the uneven temperature distribution problem caused by cascading multiple FETs for high gain.
2Device complexity
If a single temperature sensor is used to detect temperature at one position, then the device complexity is reduced, but the gain variation at other positions cannot be corrected
Solution Approach 1:
The patent applies local quality by providing temperature sensors at specific locations where temperature variations most affect performance. Temperature sensors are strategically placed in the vicinity of the main amplifier circuit and distortion signal amplifier circuit, allowing each local region to be independently monitored and compensated. This local temperature compensation ensures that gain stability is maintained at each critical position, improving overall reliability without excessive complexity.
3Device complexity
If temperature compensation is implemented using a single temperature sensor, then the control system is simpler, but the gain properties cannot be accurately compensated across the entire amplifier
Solution Approach 1:
The temperature compensation system is segmented into multiple independent measurement and control channels. Each temperature sensor independently monitors its local region, and the control circuit processes temperature data from multiple sensors separately before applying compensation. This segmentation enables accurate temperature measurement at each critical position, ensuring precise gain compensation across the entire amplifier while maintaining manageable system complexity through modular architecture.
Data Source
AI summary
According to one embodiment, a variable attenuator is arranged in an input stage, a plurality of transistors are cascaded on the later part of this variable attenuator, temperature sensors are arranged in the vicinity of two or more of the plurality of transistors to detect temperatures, the amount of gain change of the plurality of transistors is calculated from the temperature detection results individually obtained by the temperature sensors, the variable attenuator is controlled in such a manner as to reduce the amount gain change so that the input signal level can be controlled, and thereby the gain that tends to vary in accordance with temperature changes can be stabilized.