Power Amplifier Bias Circuit for Adjustable Gain Dispersion
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Solution Overview
Problem
Existing power amplifier circuits in mobile communication terminals face challenges in adjusting the range of gain dispersion, which is crucial for balancing gain linearity and power efficiency in envelope tracking schemes, as described in Japanese Unexamined Patent Application Publication No. 2014-171170.
Innovation Solution
A power amplifier circuit is designed with a first transistor, a bias current source, and an adjustment circuit that includes variable resistors and a transistor, allowing the bias current to be adjusted based on the variable power-supply voltage, thereby controlling the range of gain dispersion by altering the current paths and resistance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed bias circuit configuration is used, then the circuit structure is simple, but the gain dispersion range cannot be adjusted
Solution Approach 1:
The patent introduces variable resistors that can dynamically adjust their resistance values based on operating conditions (power supply voltage, temperature, output power). This dynamic adjustment capability allows the bias circuit to adaptively control the gain dispersion range, transforming a static circuit into a dynamic one that can optimize performance across different operating points without requiring multiple fixed circuits
Solution Approach 2:
The patent changes the resistance parameters of the bias circuit components (particularly introducing variable resistors) to adjust the bias current characteristics. By varying resistance values, the circuit can control the amount of bias current supplied to the amplifier transistor, thereby adjusting the gain dispersion range to match different operational requirements while maintaining a single circuit structure
2Use of energy by moving object
If envelope tracking is implemented with fixed gain dispersion, then power efficiency can be improved, but linearity performance deteriorates
Solution Approach 1:
The patent implements feedback mechanisms where the bias circuit monitors operating parameters (such as power supply voltage, temperature, and output power level) and automatically adjusts the bias current accordingly. This feedback control allows the system to maintain optimal gain dispersion characteristics that preserve signal linearity while operating in envelope tracking mode, preventing the degradation that would occur with fixed bias settings
Solution Approach 2:
The bias circuit dynamically adapts its characteristics in response to changing operating conditions. By continuously adjusting the bias current based on real-time parameters, the circuit maintains the appropriate balance between power efficiency and linearity performance throughout the entire operating range, rather than being optimized for a single fixed point
Data Source
AI summary
A power amplifier circuit includes a first transistor that amplifies an RF signal; a bias current source that supplies a bias current to a second terminal of the first transistor through a first current path; and an adjustment circuit that adjusts the bias current in accordance with a variable power-supply voltage supplied from a power-supply terminal. The adjustment circuit includes first to third resistors, and an adjustment transistor including a first terminal connected to the power-supply terminal through the first resistor, a second terminal connected to the bias current source through the second resistor, and a third terminal connected to the first current path through the third resistor. When the variable power-supply voltage is not less than a first voltage and not greater than a third voltage, the adjustment circuit increases a current that flows to the power-supply terminal through a second current path as the variable power-supply voltage decreases.