Dual-Amplifier RF Power Stage With Balanced Junction Temperatures
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Solution Overview
Problem
RF power amplifiers in wireless systems consume a significant portion of the power budget, particularly in devices with high peak-to-average ratio signals, leading to inefficiencies and increased power dissipation, which affects device size, cost, and reliability.
Innovation Solution
The implementation of a dual-amplifier RF amplifier system with a main amplifier and a peak amplifier, where the peak amplifier operates at a higher supply voltage and has a smaller device periphery than the main amplifier, maintaining a junction temperature ratio between 0.3 and 1.0, allowing for efficient power management and reduced device size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single RF power amplifier is used to handle high peak-to-average ratio signals, then the amplifier must be sized to handle peak power levels, but this results in poor power efficiency during low signal periods
Solution Approach 1:
The single amplifier is segmented into two separate amplifiers: a carrier amplifier sized for low signal levels and a peak amplifier sized for high signal levels. This allows each amplifier to be optimized for its specific operating range, improving overall power efficiency while handling high peak-to-average ratio signals effectively.
2Power
If the peak amplifier is continuously powered to handle high signal levels, then peak power capability is maintained, but power consumption increases significantly during low signal periods
Solution Approach 1:
The peak amplifier is activated periodically only when high signal levels are detected, rather than operating continuously. The control circuit monitors signal levels and switches the peak amplifier on during peak signal periods and off during low signal periods, thereby maintaining peak power capability while significantly reducing average power consumption.
3Loss of energy
If different supply voltages are applied to the first and second amplifiers, then power efficiency is improved, but junction temperature management becomes more complex
Solution Approach 1:
Different supply voltages are applied to different amplifiers based on their specific functions: the carrier amplifier receives a first supply voltage optimized for low-power continuous operation, while the peak amplifier receives a second supply voltage optimized for high-power peak operation. The device periphery of each amplifier is specifically designed to maintain appropriate junction temperatures under their respective operating conditions, with the ratio of device peripheries configured to balance thermal characteristics across both amplifiers.
Data Source
AI summary
In accordance with an embodiment, an RF amplifier includes: a first amplifier including a first transistor coupled to a first supply node configured to provide a first supply voltage, the first transistor having a first device periphery; a second amplifier including a second transistor coupled to a second supply node configured to provide a second supply voltage higher than the first supply voltage, the second transistor having a second device periphery; and a combining network coupled to an output of the first amplifier, an output of the second amplifier, and an RF output port. The first device periphery, the first supply voltage, the second device periphery, and the second supply voltage are configured to maintain a junction temperature ratio of between 0.3 and 1.0, and the junction temperature ratio is a ratio of a temperature of the first amplifier to a temperature of the second amplifier.