Cascode Power Amplifier Biasing for Voltage-Stress-Free Power Switching
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Solution Overview
Problem
Cascode-based power amplifiers in radar systems face reliability issues due to excessive voltage exposure when disabled, leading to reduced performance and lifespan.
Innovation Solution
Incorporating a replica cascode device in parallel with the main cascode device, controlled by a complementary activation signal, to steer current away from the main path when deactivated, thereby minimizing voltage stress and ensuring reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If cascode devices are switched off to control output power levels, then power control is achieved, but excessive voltage levels are applied to the disabled devices reducing reliability
Solution Approach 1:
A replica cascode device is introduced as an intermediary element that assumes the voltage stress when the main cascode device is turned off. The replica device acts as a mediator that protects the main device from excessive voltage by providing an alternative current path, thereby resolving the contradiction between power control capability and device reliability.
Solution Approach 2:
A replica cascode device is created as a copy of the main cascode device. This replica is controlled by a complementary signal that turns it on when the main device is off, allowing it to absorb the voltage stress. The copying principle enables the system to maintain reliability while achieving power control through the replica's protective action.
2Speed
If multiple parallel amplifier branches are used for power control, then fast power switching is achieved, but disabled branches are exposed to excessive voltage stress
Solution Approach 1:
The replica cascode device serves as a protective intermediary in each parallel amplifier branch. When a branch is disabled for fast power control, the replica device activated by the complementary signal absorbs the excessive voltage stress, preventing harm to the main cascode device while maintaining the fast switching capability of the parallel branch configuration.
Solution Approach 2:
The replica cascode device provides beforehand cushioning by being pre-configured to activate when the main device turns off. This prior protective measure ensures that when voltage stress occurs during disabled states, the replica device is already in position to absorb the stress, preventing damage before it can occur to the main device.
Data Source
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AI summary
A power amplifier stage including multiple amplifier branch circuits, in which each amplifier branch circuit includes a cascode device, a source device, and a replica cascode device. The cascode device has current terminals coupled between an output node and an intermediate node, and has a control terminal receiving a corresponding activation signal. The source device has current terminals coupled between a supply reference node and the intermediate node, and has a control terminal receiving an input signal. The replica cascode device has current terminals coupled between a supply node and the intermediate node, and has a control terminal receiving a corresponding complementary activation signals. An output power level of the power amplifier stage is controlled by asserting a selected number of activation signals and corresponding complementary activation signals for activating a selected number of the amplifier branch circuits.