Cascode Amplifier Branch Switching for Voltage Stress Protection
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Solution Overview
Problem
Sub-micron CMOS transistors in amplifiers are susceptible to stress under large signal swing conditions, affecting the reliability of amplifiers in wireless communication devices, as they are more prone to failure due to high voltage swings, especially when cascode transistors are turned off, leading to reliability and performance issues.
Innovation Solution
A cascode amplifier design with protection circuitry that includes multiple branches coupled in parallel, with switchable branches that split the voltage swing between gain and cascode transistors in both on and off states, using inductors and bias circuits to manage voltage and reduce stress on transistors, and employing switches to control the operation of transistors and manage voltage distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sub-micron CMOS transistors are used in amplifiers to reduce cost and improve integration, then manufacturing cost and integration are improved, but reliability deteriorates due to susceptibility to stress under large signal swing conditions
Solution Approach 1:
The amplifier is divided into multiple parallel branches, each containing gain transistors and cascode transistors. This segmentation allows the voltage swing to be distributed across multiple devices, reducing the stress on individual sub-micron CMOS transistors and improving reliability while maintaining the benefits of integration
Solution Approach 2:
Cascode transistors are introduced as intermediary elements between the gain transistors and the output node. These cascode transistors act as mediators that buffer the voltage swing, protecting the gain transistors from direct exposure to large voltage variations and thereby improving reliability
2Use of energy by moving object
If cascode transistors are turned off to reduce power consumption, then power consumption is reduced, but reliability deteriorates due to increased stress from large voltage swings
Solution Approach 1:
The amplifier employs dynamic branch switching where multiple parallel branches can be selectively enabled or disabled based on operating conditions. This dynamic configuration allows the system to optimize between power consumption and reliability by activating sufficient branches to handle voltage swing stress while minimizing active devices for power efficiency
3Reliability
If multiple parallel branches with switchable transistors are used to improve reliability, then reliability is improved, but device complexity increases
Solution Approach 1:
The amplifier branches are designed with universal structures where each branch contains identical gain and cascode transistor configurations. This multi-functionality allows the same structural unit to serve both signal amplification and voltage swing distribution functions, improving reliability without proportionally increasing complexity
Solution Approach 2:
Multiple amplifier branches are merged in parallel configuration, sharing common input and output nodes. This merging approach achieves reliability improvement through redundancy while minimizing the increase in complexity by consolidating shared components and structures
Data Source
AI summary
A cascode amplifier with protection circuitry is described. In one exemplary design, the amplifier includes multiple branches coupled in parallel, with at least one branch being switchable between “on” and “off” states. Each switchable branch includes a gain transistor coupled to a cascode transistor. The gain transistor amplifies an input signal and provides an amplified signal in the on state and does not amplify the input signal in the off state. The cascode transistor buffers the amplified signal and provides an output signal in the on state. The output signal swing may be split between the gain transistor and the cascode transistor in both the on and off states with the protection circuitry. Each transistor may then observe a fraction of the voltage swing. The voltage splitting in the off state may be achieved by floating the gain transistor and shorting the gate and source of the cascode transistor.