Power Amplifier Bias Circuit for Stable Input Impedance
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Solution Overview
Problem
Existing power amplification modules face challenges in suppressing changes in input impedance when gain is adjusted, leading to degraded voltage standing wave ratio (VSWR) due to the need for complex control circuits and changes in the number of operating transistors.
Innovation Solution
A power amplification module configuration that includes transistors connected in parallel with bias resistors, where bias currents are supplied to the transistors' bases to manage gain modes, ensuring that transistors are not completely switched off in low gain mode to maintain stable input impedance and VSWR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of operating transistors is changed to adjust gain, then gain adjustment is achieved, but input impedance changes and VSWR is degraded
Solution Approach 1:
The patent changes the bias current parameter supplied to transistor bases to adjust gain. By varying the bias current magnitude rather than the number of operating transistors, the invention achieves gain adjustment while maintaining relatively stable input impedance characteristics, thus resolving the contradiction between gain adaptability and impedance stability.
Solution Approach 2:
The invention dynamically adjusts the bias current supplied to the transistor bases according to different gain requirements. This dynamic parameter adjustment allows the system to adapt gain while keeping the transistor configuration constant, preventing input impedance variations that would occur with discrete transistor switching.
2Reliability
If a complicated large-scale control circuit is mounted to suppress variations in input impedance, then input impedance stability is improved, but chip area becomes larger
Solution Approach 1:
The patent uses a simple bias circuit that automatically adjusts bias currents to maintain stable input impedance without requiring complex control circuits. The bias circuit self-regulates the current distribution to transistor bases, achieving impedance stability through inherent circuit characteristics rather than active control, thus minimizing chip area.
Solution Approach 2:
Instead of using complex control circuits to manage input impedance variations, the invention changes the bias current parameters in a controlled manner to achieve both impedance stability and gain adjustment. This parameter-based approach eliminates the need for large-scale control circuits, reducing chip area while maintaining reliability.
Data Source
AI summary
Provided is a power amplification module that includes: a first transistor, a first signal being inputted to a base thereof; a second transistor, the first signal being inputted to a base thereof and a collector thereof being connected to a collector of the first transistor; a first resistor, a first bias current being supplied to one end thereof and another end thereof being connected to the base of the first transistor; a second resistor, one end thereof being connected to the one end of the first resistor and another end thereof being connected to the base of the second transistor; and a third resistor, a second bias current being supplied to one end thereof and another end thereof being connected to the base of the second transistor.