RF Amplifier Bias Control Using Supply-Triggered Attenuation
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Solution Overview
Problem
Existing radio-frequency power amplifier modules experience variations in bias current or bias voltage due to hfe variations, leading to degradation in amplifier circuit characteristics when the power supply voltage exceeds the rated voltage.
Innovation Solution
A radio-frequency circuit with an amplifier circuit, bias circuit, bias control circuit, comparing section, attenuation circuit, and control unit that compares the power supply voltage with a threshold voltage to adjust the attenuation of the attenuation circuit, thereby accurately limiting the output power of the amplifier circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power supply voltage is higher than the rated power supply voltage, then the amplifier circuit can operate with higher output power capability, but variations in hfe of the emitter follower cause variations in bias current or bias voltage, leading to degradation in amplifier circuit characteristics
Solution Approach 1:
The patent implements a feedback mechanism where the control IC monitors the power supply voltage and adjusts the bias current supplied to the emitter follower accordingly. When the power supply voltage exceeds the rated voltage, the control IC reduces the bias current to compensate for hfe variations, thereby maintaining stable amplifier circuit characteristics and preventing performance degradation.
Solution Approach 2:
The patent dynamically changes the bias current parameter based on the power supply voltage level. The control IC detects when the power supply voltage is higher than the rated voltage and adjusts the bias current parameter to an appropriate level, compensating for the effects of hfe variations and maintaining reliable amplifier operation under varying power supply conditions.
2Power
If the power supply voltage exceeds the rated voltage, then higher output power is available, but the characteristics of the amplifier circuit and electronic components degrade
Solution Approach 1:
The control IC performs preliminary anti-action by proactively adjusting the bias current before significant degradation occurs. When the power supply voltage exceeds the rated voltage, the control IC preemptively reduces the bias current to counteract the harmful effects of hfe variations, thereby preventing degradation of amplifier characteristics before they manifest.
3Device complexity
If emitter follower transistors are used for bias control, then the circuit configuration is simple, but variations in hfe cause variations in bias current when power supply voltage is high
Solution Approach 1:
The control IC acts as an intermediary between the power supply voltage and the emitter follower transistors. It monitors the power supply voltage and intermediates the bias current supply to the emitter followers, adjusting the current to compensate for hfe variations. This maintains measurement precision and bias current stability while preserving the simplicity of the emitter follower circuit configuration.
Data Source
AI summary
A radio-frequency circuit includes an amplifier circuit, a bias circuit, a bias control circuit, a comparing section, a signal input terminal, an antenna terminal, an attenuation circuit, and a control unit. The amplifier circuit includes a specific transistor. The bias circuit supplies a bias current or a bias voltage to the input terminal of the specific transistor. The bias control circuit supplies a control current or a control voltage to the bias circuit. The comparing section compares a threshold voltage with a power supply voltage of a power supply terminal connected to the output terminal of the specific transistor. The attenuation circuit is connected in a signal path between the signal input terminal and the antenna terminal and is capable of attenuating the radio-frequency signal. The control unit changes an attenuation of the attenuation circuit in accordance with a compared result of the comparing section.