Power Amplifier Bias Circuit for High-Output PAE
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Solution Overview
Problem
As output level increases, the current flowing from the bias circuit into the base of the amplification transistor in existing power amplifiers decreases power added efficiency (PAE), particularly at high output power.
Innovation Solution
The power amplifier configuration includes a first transistor for amplifying the input signal, a second transistor with power-supply voltage applied to its collector to supply bias voltage or current to the base of the first transistor, and a third transistor with a diode-connected fourth transistor to manage bias current, reducing excess current and maintaining base voltage at high output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bias circuit supplies bias current to the base of the amplification transistor, then the transistor can operate properly, but as output level increases the bias current increases causing decreased power added efficiency
Solution Approach 1:
The bias supply function is segmented into multiple independent bias circuits (first bias circuit for first transistor, second bias circuit for third transistor) rather than using a single shared bias circuit. This allows each transistor to receive optimized bias current independently, reducing total bias current consumption while maintaining proper operation of each amplification stage.
Solution Approach 2:
Each bias circuit is designed with local characteristics tailored to its specific transistor's requirements. The first bias circuit includes a first resistor connected to the base of the first transistor, while the second bias circuit includes a second resistor connected to the base of the third transistor. This localized biasing optimizes performance for each transistor's specific operating conditions, reducing overall power consumption.
2Power
If multiple transistors are used to amplify the input signal, then the amplification capability increases, but the device complexity increases
Solution Approach 1:
The first and third transistors are connected in parallel between the same power supply voltage and ground, with their collectors connected together and emitters connected to ground. This parallel configuration combines their amplification capabilities while sharing common power supply connections and ground references, reducing overall circuit complexity compared to cascaded configurations.
Solution Approach 2:
Each bias circuit serves multiple functions: it provides bias current to its associated transistor, establishes the operating point, and regulates base voltage. The first bias circuit supplies bias to the first transistor while the second bias circuit supplies bias to the third transistor, with both circuits using similar structures (transistor plus resistor) to achieve multiple objectives simultaneously.
Data Source
AI summary
A power amplifier has improved power added efficiency at high output power. The power amplifier includes: a first transistor for amplifying an input signal input to the base thereof and outputting the amplified signal from the collector thereof; a second transistor with power-supply voltage applied to the collector thereof to supply bias voltage or bias current from the emitter thereof to the base of the first transistor; a third transistor whose collector is connected to the collector of the first transistor to amplify the input signal input to the base thereof and output the amplified signal from a collector thereof; a fourth transistor whose base and collector are connected to supply bias from the emitter thereof to the base of the third transistor; and a first resistor with bias control voltage applied to one end thereof and the other end connected to the bases of the second and fourth transistors.