Distributed Amplifier Feedback Line for High-Frequency Gain
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Solution Overview
Problem
Conventional distributed amplifiers using cascode stages face challenges in maintaining high-frequency gain due to increased transmission line loss and phase differences between input and output signals, making it difficult to achieve wider bandwidth.
Innovation Solution
A distributed amplifier design that includes an input side transmission line, an output side transmission line, and multiple cascode-stage amplifiers connected in parallel, with a transmission line or inductor connected to the base terminal of the output transistor and a bias circuit applying a bias potential via this transmission line, which increases impedance on the high-frequency side and provides positive feedback, compensating for gain reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a cascode stage is used as the amplifier to reduce Miller capacitance influence, then the bandwidth is widened, but the gain on the high frequency side decreases due to increased transmission line loss and phase difference
Solution Approach 1:
The patent introduces a feedback mechanism by connecting a transmission line between the collector terminal of the output transistor and the base terminal of the output transistor. This feedback path provides positive feedback that compensates for the gain reduction on the high frequency side, thereby resolving the contradiction between bandwidth expansion and high-frequency gain maintenance
Solution Approach 2:
The patent changes the impedance parameter of the feedback transmission line to increase impedance on the high frequency side. This parameter change enables the feedback mechanism to effectively compensate for high-frequency gain loss while maintaining the broadband characteristics achieved through the cascode stage configuration
2Adaptability or versatility
If transmission line length is increased to expand bandwidth, then more amplifier stages can be accommodated, but transmission line loss increases causing gain reduction on high frequency side
Solution Approach 1:
The feedback transmission line connected to the base terminal of the output transistor provides a compensatory mechanism that counteracts the energy loss in the input and output transmission lines. The positive feedback reinforces the high-frequency signals that have undergone attenuation, thereby compensating for transmission line loss while maintaining expanded bandwidth
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
This design achieves a peaking effect on the high-frequency side, thereby expanding the bandwidth by approximately 50% compared to conventional configurations, allowing for wider band amplification.
Implementation Method 1
positive feedback is applied from an emitter terminal of the output transistor to a collector terminal thereof
Implementation Method 2
impedance of the transmission line connected to the output transistor of the amplifier increases on a high frequency side
Implementation Method 3
influence of the Miller capacitance between the collector and the base of the input transistor is reduced
Data Source
AI summary
In a distributed amplifier, a plurality of cascode amplifiers connected in parallel between an input side transmission line and an output side transmission line are provided, a transmission line is connected to an input terminal of an output transistor of each of the amplifiers, and a bias potential is applied from a bias circuit to the input terminal of the output transistor via the transmission line.