Split Cascode LNA Supply Switching for OFF-State Voltage Stress
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Solution Overview
Problem
Low noise amplifiers (LNAs) in communications receivers face challenges with high voltages across output transistors when turned OFF, risking time-dependent dielectric breakdown and impacting noise figure and third-order intercept point, especially when using thinner gate oxide layers to minimize noise.
Innovation Solution
The implementation of a receiver front end with multiple LNA branches, where the ON/OFF states are controlled by switching the power supply connection using high-voltage tolerant switches with thick gate oxide layers, allowing the use of thinner gate oxide layers for output transistors, thereby reducing operational voltages and improving noise figure and third-order intercept.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thinner gate oxide layers are used for output transistors to minimize noise, then noise figure is improved, but the transistors become vulnerable to time-dependent dielectric breakdown from high OFF-state voltages
Solution Approach 1:
The patent introduces high-voltage tolerant switches with thick gate oxide layers as intermediary components between the power supply and the low-noise output transistors. These switches act as mediators that block high OFF-state voltages from reaching the thin gate oxide layers of the output transistors, while still enabling proper amplification during ON-state operation
Solution Approach 2:
The patent segments the transistor switching function from the amplification function. High-voltage tolerant switches handle the power supply connection and voltage blocking, while separate low-noise output transistors handle signal amplification. This segmentation allows each component to be optimized for its specific function without compromise
2Reliability
If high-voltage tolerant switches with thick gate oxide layers are used to control power supply connection, then transistor reliability is improved, but device complexity increases
Solution Approach 1:
The high-voltage tolerant switches perform multiple functions: they control the power supply connection to output transistors, block high OFF-state voltages, and enable proper amplification during ON-state. This multi-functionality reduces the need for additional protective components, offsetting the increased complexity of using high-voltage tolerant switches
Data Source
AI summary
A receiver front end capable of receiving and processing intraband non-contiguous carrier aggregate (CA) signals using multiple low noise amplifiers (LNAs). Cascode circuits, each having a “common source” configured input FET and a “common gate” configured output FET, serve as the LNAs. An amplifier-branch control switch, configured to withstand relatively high voltage differentials by means of a relatively thick gate oxide layer and coupled between a terminal of the output FET and a power supply, controls the ON and OFF state of each LNA while enabling use of a relatively thin gate oxide layer for the output FETs, thus improving LNA performance. Some embodiments may include a split cascode amplifier and/or a power amplifier.