Distributed Amplifier Active Termination for Low Noise Linearity
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Solution Overview
Problem
Distributed amplifiers face challenges in achieving a large gain-bandwidth product with wide operating bandwidth while maintaining linearity and efficiency, particularly in RF and optical fiber communications, due to phase velocity variations and distortions.
Innovation Solution
The design incorporates a distributed amplifier with multiple amplifier sections featuring inductive elements and active impedance termination circuits, utilizing cascode configurations and localized feedback to minimize noise and maximize linearity, allowing for baseband amplification across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If distributed amplifiers use multiple transconductance elements coupled together to increase gain-bandwidth product, then the gain-bandwidth product is improved, but phase velocity variations and distortions occur that degrade linearity and efficiency
Solution Approach 1:
The patent transforms the traditional resistive termination approach into an active impedance termination using a transistor circuit. This changes the termination parameter from a simple resistance to a dynamic impedance that can be controlled and optimized, achieving both high gain-bandwidth product and improved linearity simultaneously
Solution Approach 2:
The active impedance termination circuit incorporates feedback mechanisms that monitor and correct phase velocity variations and distortions in real-time. This feedback control compensates for the degradation effects, maintaining linearity while preserving the high gain-bandwidth product achieved through multiple transconductance elements
2Duration of action of moving object
If capacitive-coupled distributed amplifiers are used to extend gain-bandwidth products, then the gain-bandwidth product is improved, but baseband operation capability is lost
Solution Approach 1:
The patent introduces an active impedance termination circuit as an intermediary element that bridges the gap between high-frequency and baseband operations. This intermediary component enables the amplifier to handle both baseband signals and high-frequency signals across the entire spectrum, achieving universal operation from baseband to microwave frequencies
Solution Approach 2:
The distributed amplifier with active impedance termination is designed to perform multiple functions across different frequency ranges. The same amplifier structure can operate as a baseband amplifier, RF amplifier, or microwave amplifier depending on the input signal frequency, providing universal amplification capability from baseband to microwave frequencies
Data Source
AI summary
The present disclosure describes a distributed amplifier (DA) that includes active device cells within sections that are configured to provide an input gate termination that is conducive for relatively low noise and high linearity operation. A section adjacent to an output of the DA is configured to effectively terminate the impedance of an input transmission line of the DA. Each active device cell includes transistors coupled in a cascode configuration that thermally distributes a junction temperature among the transistors. In this manner, noise generated by a common source transistor of the cascode configuration is minimized. The transistors coupled in the cascode configuration may be fabricated using gallium nitride (GaN) technology to reduce physical size of the DA and to further reduce noise.