Variable RF Matching Circuit for Power Amplifier Linearity
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Solution Overview
Problem
Power amplifiers in wireless communication devices suffer from distortion due to nonlinear input capacitance, which degrades their performance and linearity.
Innovation Solution
The use of a P-channel metal oxide semiconductor (PMOS) transistor to compensate for the nonlinear input capacitance of N-channel metal oxide semiconductor (NMOS) transistors in power amplifiers, along with variable input impedance matching circuits that include a series inductor and a shunt variable capacitor, to improve linearity and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large transistors are used to provide high output power, then power output is improved, but distortion increases due to large nonlinear input capacitance
Solution Approach 1:
An intermediary circuit (input matching network with variable capacitor) is introduced between the driver amplifier and power amplifier to compensate for the nonlinear input capacitance of the power amplifier, thereby reducing distortion while maintaining high output power capability
Solution Approach 2:
The capacitance value in the input matching network is dynamically changed based on the power level to compensate for the nonlinear input capacitance of the power amplifier transistors, improving linearity across different operating conditions
2Device complexity
If fixed impedance matching is used, then circuit simplicity is maintained, but linearity degrades at varying power levels due to nonlinear input capacitance
Solution Approach 1:
The input matching network transitions from a fixed impedance design to a dynamic design where the capacitance value changes with power level, allowing the circuit to adapt to varying operating conditions and maintain optimal linearity
Solution Approach 2:
The system automatically adjusts the matching network capacitance based on the power level without requiring external intervention, using the power level information to self-regulate the input impedance matching and maintain linearity
Data Source
AI summary
Techniques for reducing distortion and improving linearity of amplifiers are described. In an exemplary design, an apparatus includes a driver amplifier, a variable matching circuit, and a power amplifier. The driver amplifier amplifies a first RF signal and provides a second RF signal. The variable matching circuit receives the second RF signal and provides a third RF signal. The power amplifier amplifies the third RF signal and provides a fourth RF signal. The variable matching circuit matches a fixed impedance at the output of the driver amplifier to a variable impedance at the input of the power amplifier in order to improve the linearity of the amplifiers. In an exemplary design, the power amplifier includes a first transistor (e.g., an NMOS transistor) of a first type, and the variable matching circuit includes a second transistor (e.g., a PMOS transistor) of a second type that is different from the first type.