Power Amplifier Bias Current Rerouting for Gain Dispersion Control
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Solution Overview
Problem
Existing power amplifier circuits for mobile communication terminals have gain-dispersion characteristics that do not match customer requirements, particularly when the power supply voltage changes, affecting the performance of envelope-tracking power supply circuits.
Innovation Solution
A power amplifier circuit with a matching circuit, a transistor, a bias current source, and an adjustment circuit that adjusts the bias current based on variable power supply voltage, allowing the transistor to operate as two P-N junction diodes within specific voltage ranges, thereby reducing bias current and improving gain-dispersion characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bias circuit with an emitter follower transistor and constant voltage generation circuit is used, then the power amplifier can operate with a simple bias control mechanism, but the gain-dispersion characteristics do not match customer requirements when power supply voltage changes
Solution Approach 1:
The bias circuit dynamically adjusts the bias current based on the power supply voltage level. When the power supply voltage is low (first voltage range), the bias current is increased to maintain adequate transistor operation. When the power supply voltage is high (second voltage range), the bias current is decreased to prevent excessive gain and improve linearity. This dynamic adaptation resolves the contradiction by making the bias circuit responsive to voltage changes rather than static.
Solution Approach 2:
The invention changes the operating parameters of the bias circuit based on the power supply voltage. Specifically, it modifies the bias current magnitude according to the voltage range detected. This parameter change allows the same bias circuit to provide optimal performance across different voltage conditions, improving gain-dispersion characteristics without requiring multiple separate circuits.
2Adaptability or versatility
If the power supply voltage to the transistor changes, then the transistor can adapt to different operating conditions, but the gain dispersion increases and does not meet customer requirements
Solution Approach 1:
The bias circuit incorporates feedback mechanisms that sense the power supply voltage level and automatically adjust the bias current accordingly. This feedback loop ensures that as the power supply voltage changes, the bias current is modulated to compensate for gain variations, thereby maintaining consistent gain-dispersion characteristics across different voltage conditions.
Solution Approach 2:
The bias circuit takes preliminary action by preemptively adjusting the bias current in response to detected voltage changes before they can cause significant gain dispersion. By anticipating and counteracting the effects of voltage variation through proactive bias adjustment, the circuit prevents gain dispersion from occurring in the first place.
Data Source
AI summary
A power amplifier circuit includes a transistor, a bias current source, and an adjustment circuit. The transistor amplifies an RF signal when supplied with a variable power supply voltage. The bias current source supplies a bias current to the base of the transistor through a first current path. The adjustment circuit increases a current flowing from the bias current source to an input terminal of a matching circuit through a second current path as the variable power supply voltage decreases, and decreases the bias current flowing from the bias current source to the base of the transistor through the first current path as the current flowing from the bias current source to the input terminal through the second current path increases.