Power Amplifier Bias Feedback for Stable Low-Power Control
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Solution Overview
Problem
Existing power amplifier circuits face reduced controllability in low-output-power regions due to reliance on bias current magnitude, leading to potential amplifier activation despite intended shutdown, and inadequate control over output power variations from factors like temperature and power supply changes.
Innovation Solution
A power amplifier circuit design incorporating transistors and control circuits that regulate bias current and voltage based on reference signals and currents, utilizing control voltage and current generation circuits to stabilize output power by compensating for variations in current amplification, temperature, and power supply changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a variable-voltage circuit is used to control gain by adjusting power supply voltage, then output power can be controlled, but voltage drop in the variable-voltage circuit causes reduction in variable power supply voltage and output power
Solution Approach 1:
The patent changes the control parameter from power supply voltage to bias current. By controlling the bias current supplied to the amplifier, the gain and output power are adjusted without introducing a variable-voltage circuit that would cause voltage drop and energy loss.
2Power
If bias current is controlled to adjust gain, then output power control is achieved, but in low-output-power region the bias current magnitude remains not less than predetermined value preventing amplifier shutdown
Solution Approach 1:
The patent segments the control range into multiple regions. A first control circuit handles normal operation with bias current control, while a second control circuit activates in the low-output-power region to enable amplifier shutdown. This segmentation allows full controllability across all output power levels.
Solution Approach 2:
The patent implements dynamic control by switching between different control modes based on the desired output power level. The control system adapts its behavior: using bias current adjustment for normal operation and enabling shutdown capability for low-power regions, thereby achieving complete controllability.
3Reliability
If bias current is increased to achieve predetermined gain, then amplification is maintained, but amplifier cannot be turned off even when desired to be shut down
Solution Approach 1:
The patent divides the control system into two segments: a first control circuit for maintaining gain through bias current control during normal operation, and a second control circuit for enabling amplifier shutdown in low-power regions. This allows both reliability and adaptability to be satisfied.
Solution Approach 2:
The control system includes circuitry that automatically determines when to enable shutdown based on the desired output power level. The system self-regulates by activating the shutdown capability only when appropriate, maintaining reliability during normal operation while providing adaptability when needed.
Data Source
AI summary
A power amplifier circuit includes: a transistor which is supplied at a base with a bias current, amplifies an input signal, and outputs a current; a transistor which is connected at a base to the base of the transistor and in which a current commensurate with the current is input to a collector; a transistor which outputs a bias control signal which controls supply of the bias current; and a control circuit which is connected to the collector of the transistor and a gate of the transistor and controls a bias control signal on the basis of a reference current based on a reference signal and the current.