Asymmetrical Push-Pull RF Power Amplifier for High-Power Linearity
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Solution Overview
Problem
RF power amplifiers face nonlinear behavior at high input powers, leading to harmonic distortion and loss of linearity, making it difficult to maintain maximum linearity over a wide power range, especially in digital modulations with high amplitude signals.
Innovation Solution
The implementation of an asymmetrical push-pull operation in dual-transistor RF power amplifiers, where the gate voltages of the transistors are controlled independently to compensate for self-biasing, allowing for improved AM/AM and AM/PM transfer functions, and linearity is maintained by storing optimal gate voltage values as a function of frequency, power, and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the amplifier operates at high power levels, then the output power increases, but the linearity deteriorates due to nonlinear behavior and saturation
Solution Approach 1:
The patent applies asymmetry by using different quiescent currents for the two transistors in the push-pull configuration. Instead of symmetric operation where both transistors have identical bias conditions, the invention deliberately creates asymmetric biasing with different DC gate voltages (VGS1 and VGS2) to compensate for self-biasing effects and maintain linearity across a wide power range including high power levels.
Solution Approach 2:
The patent changes the operational parameters by dynamically adjusting the DC gate voltages of the transistors based on the instantaneous power level. The control stage modifies the bias conditions in real-time according to the signal amplitude, allowing the amplifier to maintain optimal linearity characteristics whether operating at low or high power levels.
2Manufacturing precision
If the amplifier operates at low power levels with high linearity, then the linearity improves, but the power output is limited due to quick saturation
Solution Approach 1:
The patent implements dynamic operation by continuously adapting the bias conditions of the transistors according to the instantaneous power level. The control stage dynamically adjusts the DC gate voltages in real-time, allowing the amplifier to transition smoothly between different operating regions and maintain high linearity across the entire power range from low to high levels.
3Manufacturing precision
If digital predistortion is applied to maintain linearity, then the linearity performance improves, but the device complexity increases due to additional hardware and control requirements
Solution Approach 1:
The patent applies self-service by making the amplifier inherently linear through asymmetric push-pull operation rather than requiring external correction systems. The amplifier compensates for its own nonlinearities through the asymmetric biasing configuration, eliminating the need for additional digital predistortion hardware, servo control systems, or RF delay management components.
Data Source
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AI summary
Since the transistors (Q1, Q2) are push-pull controlled field-effect transistors, during the operation of the amplifier, the transistors operate asymmetrically, with different drain-source currents in the on-state. As the currents are controlled by the gate voltages of the transistors (Q1, Q2), the values of these voltages are functions of operating parameters, and the pairs of these values as functions of these parameters are stored in a memory (21) accessible to the amplifier.