Cascode Power Amplifier Biasing for Voltage-Stress-Free Branch 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 branches are not properly managed, leading to reduced reliability over time.
Innovation Solution
Implementing a replica cascode device in parallel with the cascode device, controlled by complementary activation signals, to divert current away from the main path when the amplifier branch is deactivated, thereby avoiding excessive voltage stress on the cascode device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If cascode-based amplifiers are configured into multiple parallel branches for fast power switching, then power switching speed is improved, but disabled cascode devices are exposed to excessive voltage levels that reduce reliability
Solution Approach 1:
A replica cascode device is introduced as an intermediary component connected in parallel with the main cascode device. When the main cascode device is turned off, the replica cascode device remains active and serves as a mediator to provide an alternative current path, preventing excessive voltage from appearing across the main cascode device while maintaining fast switching capability through parallel branch configuration
2Adaptability or versatility
If multiple parallel amplifier branches are used for power control, then power level flexibility is improved, but disabled branches experience voltage stress that reduces reliability
Solution Approach 1:
The amplifier is divided into multiple independent parallel branches, each with its own cascode device that can be independently controlled. This segmentation allows flexible power level control by activating or deactivating specific branches while the replica cascode device in each branch protects the main cascode device from voltage stress during deactivation
3Use of energy by moving object
If cascode devices are switched off for power control, then power consumption is reduced, but excessive voltage exposure during switching reduces reliability
Solution Approach 1:
The replica cascode device is configured to remain active beforehand when the main cascode device is turned off. This prior cushioning approach ensures that a safe current path exists before voltage stress can damage the main cascode device, allowing power consumption to be reduced by switching off main devices while protecting them from reliability-degrading voltage exposure
Data Source
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.