Power Amplifier Bias Limiting for Higher PAE at Variable Voltage
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Solution Overview
Problem
Conventional power amplifiers using emitter-grounded bipolar transistors do not significantly improve power-added efficiency (PAE) due to a constant DC bias current, which limits the reduction of power consumption despite varying power supply voltage with high-frequency signal amplitude.
Innovation Solution
A power amplification circuit with a variable voltage power supply, a bias circuit providing adjustable DC bias current, and a current limiting circuit that optimizes the DC bias current based on the power supply voltage, allowing for dynamic adjustment of collector current to enhance PAE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the power supply voltage is varied in accordance with the envelope of the high-frequency signal, then the power consumption of the power amplifier is reduced, but the power-added efficiency is not significantly improved due to constant DC bias current
Solution Approach 1:
The patent applies dynamics by making the DC bias current variable instead of constant. The bias circuit includes a constant current amplification transistor whose base-emitter voltage is controlled by an envelope signal, causing the DC bias current to vary dynamically with the signal envelope. This dynamic adjustment of DC bias current in conjunction with dynamic power supply voltage variation significantly improves power-added efficiency.
Solution Approach 2:
The patent changes the parameter of DC bias current from constant to variable. By controlling the base-emitter voltage of the constant current amplification transistor with the envelope signal, the DC bias current parameter is made to follow the envelope variations. This parameter change enables the collector-emitter current to be strongly correlated with the envelope, thereby improving power-added efficiency.
2Ease of operation
If the DC bias current is kept substantially constant, then the circuit is simple to operate, but the power-added efficiency cannot be significantly improved
Solution Approach 1:
The patent transitions from static (constant) DC bias current to dynamic (variable) DC bias current. The constant current amplification transistor's base-emitter voltage is controlled by the envelope signal, creating a dynamic system where the DC bias current automatically adjusts with signal conditions. This maintains ease of operation while dramatically improving power-added efficiency.
Solution Approach 2:
The patent introduces feedback by using the envelope signal to control the base-emitter voltage of the constant current amplification transistor. The envelope detector extracts the envelope from the high-frequency signal, and this envelope signal is fed back to control the DC bias current, creating a closed-loop system that optimizes power-added efficiency while maintaining simple operation.
Data Source
AI summary
A power amplification circuit includes an amplification transistor, a variable voltage power supply that supplies a variable voltage to a collector of the amplification transistor, a bias circuit that has a constant current amplification transistor outputting a DC bias current to a base of the amplifier transistor, and a current limiting circuit that limits the DC bias current. The current limiting circuit includes a current limiting transistor, a resistor element connected to a collector of the current limiting transistor and the variable voltage power supply, and a resistor element connected to a base of the current limiting transistor and a base of the constant current amplifying transistor.