Switched-Branch Cascode LNA for Thin-Oxide Overvoltage Protection
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Solution Overview
Problem
Multi-branch amplifiers face performance degradation due to the inability to protect transistors in deactivated branches from voltage levels higher than their tolerable limits, especially when using thin-oxide transistors and limited supply voltages.
Innovation Solution
A multi-branch cascode amplifier with a protection circuit that includes switching arrangements to decouple the drain of the output transistor from the common output node and couple a reference voltage during the OFF state of one branch, ensuring the transistors operate within their maximum tolerable voltages, even when the amplifier is powered by a supply voltage higher than the thin-oxide transistor's limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the amplifier is powered by a supply voltage higher than the thin-oxide transistor's limit to achieve higher power and voltage outputs, then the power and voltage output capability is improved, but the transistors in deactivated branches are exposed to voltage levels higher than their tolerable limits causing performance degradation
Solution Approach 1:
The amplifier is divided into multiple independent branches, each with its own protection mechanism. The switching arrangements are segmented and distributed across different branches, allowing independent control and protection of each branch's transistors from overvoltage conditions.
Solution Approach 2:
Switching arrangements act as intermediary elements between the high-voltage supply and the thin-oxide transistors. These switches mediate the voltage connection, enabling the transistors to operate at higher supply voltages while preventing excessive voltage from reaching the transistor terminals during OFF states.
2Reliability
If switching arrangements are added to protect transistors in deactivated branches, then transistor voltage compliance is improved, but the device complexity increases
Solution Approach 1:
The switching arrangements serve multiple functions: they act as protection elements for voltage compliance, function as branch selection switches for activating/deactivating specific amplifier branches, and provide control mechanisms for power management. This multi-functionality reduces the need for separate dedicated protection components.
Solution Approach 2:
The protection function is merged with the existing branch control switching structure. The same switching arrangements that control branch activation are also used for voltage protection, combining two functions into a single circuit element rather than adding separate protection components.
Data Source
AI summary
Methods and circuital arrangements for turning OFF branches of a multi-branch cascode amplifier are presented. First and second switching arrangements coupled to a branch allow turning OFF the branch while protecting transistors of the branch from a supply voltage that may be greater than a tolerable voltage of the transistors. The first switching arrangement includes a transistor-based switch that is in series connection with the transistors of the branch. The first switching arrangement drops the supply voltage during the OFF state of the branch and provides a conduction path for a current through the branch during the ON state of the branch. A resistor and a shunting switch are coupled to a gate of the transistor-based switch to reduce parasitic coupling effects of the transistor-based switch upon an RF signal coupled to the branch during the ON state and OFF state of the branch.