Cascode Distributed Amplifier Gain Control Without Band Degradation
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Solution Overview
Problem
Existing distributed amplifiers face challenges in achieving variable gain without deteriorating band characteristics, as methods like changing terminating resistance or adjusting transistor bias lead to impedance mismatching and band characteristic degradation.
Innovation Solution
A distributed amplifier design with cascode-connected transistors and a variable resistance circuit, where the set voltage equals the DC potential of the connecting point, allows for gain adjustment without altering the bias condition, maintaining band characteristics by applying a power supply voltage that accounts for current and resistance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the terminating resistance value is changed to adjust gain, then the gain can be varied, but impedance mismatching occurs and ripples are generated in the frequency characteristic
Solution Approach 1:
The patent introduces a variable resistance element connected to the connecting point between the first and second transistors as an intermediary component. This variable resistance acts as a mediator to adjust the gain by changing the DC potential at the connecting point, while the set voltage serves as a reference to maintain proper bias conditions. This intermediary approach allows gain control without directly altering the terminating resistance, thereby avoiding impedance mismatching and frequency characteristic degradation.
2Adaptability or versatility
If the bias voltage of the input transistor is changed to adjust gain, then the gain can be varied, but the band characteristic deteriorates due to deviation from optimal bias point
Solution Approach 1:
The patent segments the gain control function from the bias control function. The variable resistance element is specifically connected to control only the DC potential at the connecting point between transistors, while the bias voltage applied to the input transistor remains separate and unchanged. This segmentation allows independent adjustment of gain through the variable resistance without affecting the optimal bias conditions of the input transistor, thereby maintaining high operating speed and band characteristics.
3Adaptability or versatility
If the DC potential of the connecting point is changed to adjust gain, then the gain can be varied, but the bias condition is altered and band characteristic deteriorates
Solution Approach 1:
The patent applies the equipotentiality principle by introducing a set voltage that references the proper DC potential level. The variable resistance element adjusts the DC potential at the connecting point, but the set voltage serves as a reference to maintain the bias condition. By establishing this equipotential reference, the system can vary gain through DC potential adjustment while preventing deterioration of the bias condition, as the set voltage ensures the potential remains within the proper operating range.
Data Source
AI summary
A unit amplifier has first and second transistors, which are cascode-connected, and a first variable resistance circuit. A base terminal or a gate terminal of the first transistor is connected to a cell input terminal, a collector terminal or a drain terminal of the second transistor is connected to a cell output terminal, an emitter terminal or a source terminal of the second transistor is connected to a collector terminal or a drain terminal of the first transistor, and one end of the first variable resistance circuit is connected to a connecting point of the first and second transistors.