Bias-Tuned Cascode Distributed Amplifier for Linearity-Bandwidth Tradeoff
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Solution Overview
Problem
Current broadband gallium nitride (GaN) distributed amplifiers face a trade-off between linearity and gain-bandwidth, limiting high-linearity DAs to less than 20 GHz microwave frequencies.
Innovation Solution
The distributed amplifier design incorporates a cascode configuration with a common-drain cascode amplifier cell, featuring a main transistor and a cascode transistor, along with an input transistor in a common-drain configuration, coupled with current source circuitry for bias tuning, which enhances linearity and gain-bandwidth by adjusting current flow through the current source control terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If efforts are made to increase linearity in distributed amplifiers, then third-order intercept point improves, but gain-bandwidth is reduced
Solution Approach 1:
The amplifier is divided into multiple identical amplifier cells connected in parallel, each contributing to the overall gain while maintaining linearity. The segmentation allows the amplifier to achieve high linearity through the distributed architecture without sacrificing gain-bandwidth product
Solution Approach 2:
The amplifier employs dynamic bias tuning through current source circuitry that can adjust operating conditions in real-time. This dynamic control enables optimization of both linearity and gain-bandwidth based on operating requirements, resolving the static trade-off between these parameters
2Speed
If distributed amplifier operates at millimeter-wave frequencies, then frequency range extends, but maintaining high linearity becomes difficult
Solution Approach 1:
The amplifier uses parameter tuning through bias control circuitry to optimize performance at millimeter-wave frequencies. By dynamically adjusting bias conditions and operating parameters, the amplifier maintains high linearity (IP3) across the extended frequency range up to 40 GHz and beyond
Solution Approach 2:
Multiple identical amplifier cells are used in a distributed configuration, where each cell is a precise copy of the others. This copying approach ensures consistent linearity performance across all frequency bands, enabling millimeter-wave operation while maintaining high IP3
3Measurement precision
If cascode configuration is used to improve linearity, then third-order intercept point increases, but power dissipation increases
Solution Approach 1:
The bias tuning circuitry provides partial adjustment capability, allowing optimization of linearity only when needed. The system can operate in a balanced mode that achieves sufficient linearity improvement without the full power penalty of aggressive bias tuning, thus reducing overall power dissipation
Data Source
AI summary
A distributed amplifier (DA) is disclosed. The DA includes a first plurality of inductive elements coupled in series forming a first plurality of connection nodes. The DA also includes a second plurality of inductive elements coupled in series forming a second plurality of connection nodes. The DA further includes a plurality of amplifier cells that each has a main transistor and a cascode transistor coupled into a cascode configuration. The cascode transistor has a current input coupled to a corresponding one of the first plurality of connection nodes. An input transistor has a control terminal coupled to a corresponding one of the second plurality of connection nodes, a current input terminal configured to provide a bias tuning for the DA, and a third current output terminal coupled to a control terminal of the main transistor and configured to provide a separate bias tuning for the DA.