Mode-Switched Bias Circuit in Power Amplifiers for Linearity
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Solution Overview
Problem
Power amplifier modules in mobile communication devices face challenges in maintaining high linearity across wide dynamic ranges while minimizing power consumption, especially when operating in multiple modes such as envelope tracking and average power tracking.
Innovation Solution
A power amplifier module with a bias circuit that includes first and second transistors and resistors, where the transistors are turned ON/OFF based on specific bias control voltages to optimize bias current supply according to operation modes, allowing for suitable bias control across different operation modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high power supply voltage is used to maintain high linearity across wide dynamic range, then linearity is improved, but power consumption increases
Solution Approach 1:
The bias circuit dynamically adjusts the bias control voltage supplied to the amplifier transistor based on the operation mode (envelope tracking or average power tracking). This dynamic adjustment allows the system to optimize linearity for each mode without continuously operating at high power supply voltage, thereby reducing overall power consumption while maintaining high linearity when needed.
2Device complexity
If a single bias circuit configuration is used for all operation modes, then device complexity is reduced, but adaptability to different operation modes deteriorates
Solution Approach 1:
The bias circuit is segmented into multiple parallel paths, each containing a transistor and resistor pair. The first transistor with first resistor is optimized for envelope tracking mode, while the second transistor with second resistor is optimized for average power tracking mode. This segmentation allows the circuit to provide mode-specific bias control without requiring completely separate bias circuits for each mode.
Solution Approach 2:
The bias circuit dynamically switches between different transistor-resistor paths based on the operation mode. By adjusting which transistor is active (turned ON) depending on whether envelope tracking or average power tracking is being used, the circuit adapts its characteristics to optimize performance for each mode while maintaining a single integrated structure.
Data Source
AI summary
A power amplifier module includes an amplifier transistor and a bias circuit. A first power supply voltage based on a first operation mode or a second power supply voltage based on a second operation mode is supplied to the amplifier transistor. The amplifier transistor receives a first signal and outputs a second signal obtained by amplifying the first signal. The bias circuit supplies a bias current to the amplifier transistor. The bias circuit includes first and second resistors and first and second transistors. The first transistor is connected in series with the first resistor and is turned ON by a first bias control voltage which is supplied when the first operation mode is used. The second transistor is connected in series with the second resistor and is turned ON by a second bias control voltage which is supplied when the second operation mode is used.