Dynamic Bias Control in Power Amplifiers for Wider Gain Dispersion
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Solution Overview
Problem
Existing power amplifier circuits have limited gain dispersion when the power supply voltage changes, which restricts their efficiency and performance in mobile communication terminals.
Innovation Solution
A power amplifier circuit design that includes a first transistor with a base supplied with an RF signal and a collector supplied with a variable power supply voltage, a bias circuit with a second transistor, and a bias adjustment circuit that decreases the bias current to the base of the first transistor as the power supply voltage decreases, thereby broadening the gain dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant bias current is supplied to the transistor base, then the transistor operates stably, but the gain dispersion relative to power supply voltage changes is limited
Solution Approach 1:
The bias circuit transitions from a static constant current source to a dynamic bias circuit that automatically adjusts the bias current according to power supply voltage changes. The dynamic bias circuit uses a control signal generated from the power supply voltage to modulate the bias current, enabling the system to adapt to varying operating conditions while maintaining optimal performance.
Solution Approach 2:
The dynamic bias circuit implements a feedback mechanism where the power supply voltage is sensed and used to generate a control signal that adjusts the bias current. This feedback loop ensures that the bias current automatically compensates for power supply voltage variations, thereby broadening the gain dispersion and improving the transistor's adaptability to different operating conditions.
2Use of energy by moving object
If the power supply voltage is increased to improve efficiency, then power-added efficiency increases, but gain flatness deteriorates due to limited gain dispersion
Solution Approach 1:
The system dynamically changes the bias current parameter in response to power supply voltage changes. By adjusting the bias current according to the power supply voltage level, the dynamic bias circuit enables the transistor to operate efficiently across a wider range of power supply voltages while maintaining gain flatness, thus resolving the trade-off between efficiency and gain stability.
3Device complexity
If a simple bias circuit is used, then device complexity is low, but the ability to broaden gain dispersion is insufficient
Solution Approach 1:
The dynamic bias circuit is designed to perform multiple functions: it serves as a bias current source while simultaneously providing gain dispersion broadening and power supply voltage compensation. This multi-functional design achieves enhanced performance without proportionally increasing device complexity, as the same circuit structure accomplishes multiple objectives.
Data Source
AI summary
A power amplifier circuit includes a first transistor having a base supplied with an RF signal and a collector supplied with a variable power supply voltage corresponding to a level of the RF signal, the first transistor being configured to amplify the RF signal, a bias circuit including a second transistor that supplies a bias current to the base of the first transistor, and a bias adjustment circuit that decreases a current to be supplied from an emitter of the second transistor as the variable power supply voltage decreases, thereby decreasing the bias current to be supplied to the base of the first transistor.