Switched-Branch Cascode LNA Protection for High Supply Voltage
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Solution Overview
Problem
Multi-branch amplifier architectures 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 a branch, maintaining operation within maximum tolerable voltages, allowing the use of thin-oxide transistors across all branches without performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If higher supply voltages are used to improve amplification performance, then power and voltage output capability is improved, but thin-oxide transistors in deactivated branches are damaged due to voltage exceeding their tolerable limits
Solution Approach 1:
A protection circuit is introduced as an intermediary between the high-voltage supply and the thin-oxide transistors. This protection circuit includes switching arrangements that actively monitor and control the voltage across transistors in deactivated branches, preventing voltage from exceeding tolerable limits while allowing the amplifier to operate at higher supply voltages when branches are active.
Solution Approach 2:
The amplifier architecture dynamically adjusts the voltage conditions across transistors based on the operational state of different branches. When a branch is deactivated, the protection circuit dynamically switches to a protective mode that limits the voltage across its transistors. When the branch is activated, the protection circuit dynamically transitions to allow full voltage operation for optimal amplification performance.
2Reliability
If switching arrangements are added to protect transistors in deactivated branches, then transistor protection is improved, but device complexity increases
Solution Approach 1:
The protection circuit is designed with multi-functional switching arrangements that serve dual purposes: they act as protection switches when branches are deactivated and as normal signal path components when branches are activated. This universal design allows the same circuit elements to provide both protection functionality and maintain normal amplifier operation, reducing the need for entirely separate protection circuits for each branch.
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.