Unbalanced Linear Power Amplifier with Quadrature Coupler
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Solution Overview
Problem
Existing RF amplifiers face challenges in achieving 3 dB or better linear power amplification without compromising bandwidth or linear efficiency, and require at least a 4 dB EVM linearity improvement across a greater than 20% bandwidth.
Innovation Solution
An unbalanced linear power amplifier configuration is employed, utilizing a quadrature coupler with biasing circuitry and a tuning network that includes isolation inductance and resistance, dynamically tunable to optimize performance across different frequencies, thereby minimizing error vector magnitude (EVM) and maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two power amplifiers are combined to increase linear output power, then power output increases by at least 3 dB, but bandwidth or linear efficiency may be compromised
Solution Approach 1:
The patent employs asymmetric tuning networks with different isolation resistance values (Riso1 and Riso2) for each amplifier path. By setting Riso1 between 0.02*Ro and 0.8*Ro, and Riso2 between 0.2*Ro and 5*Ro with Riso2 > Riso1, the system creates deliberate asymmetry to optimize broadband performance while maintaining power combination. This asymmetric configuration allows independent optimization of each amplifier's contribution across the bandwidth, resolving the contradiction between power output and bandwidth preservation.
Solution Approach 2:
The patent implements dynamically tunable isolation resistance and inductance values in the tuning networks. The controller adjusts these parameters based on the operating frequency to maintain optimal performance across the broadband range. This dynamic adaptation allows the system to preserve bandwidth while combining amplifier outputs, as the tuning networks continuously optimize the impedance matching and power combination ratio across different frequency points.
2Power
If two power amplifiers are combined to increase linear output power, then power output increases by at least 3 dB, but linear efficiency may be compromised
Solution Approach 1:
The patent applies local quality optimization by providing separate, independently tunable tuning networks for each amplifier path. Each tuning network (with Riso1, Liso1 for the first amplifier and Riso2, Liso2 for the second amplifier) can be optimized locally to maximize the efficiency of that specific amplifier's contribution to the combined output. This local optimization ensures that each amplifier operates at peak efficiency while contributing to the overall power increase, preventing efficiency degradation from suboptimal operating points.
3Power
If two power amplifiers are combined without proper tuning, then power output increases, but EVM linearity deteriorates
Solution Approach 1:
The patent systematically changes critical parameters (isolation resistance and inductance values) to optimize EVM linearity. By setting Riso1 between 0.02*Ro and 0.8*Ro and Riso2 between 0.2*Ro and 5*Ro with Riso2 > Riso1, along with corresponding inductance values, the system achieves at least 4 dB EVM linearity improvement. The controller dynamically adjusts these parameters based on frequency to maintain optimal linearity across the broadband range, ensuring that power combination does not degrade signal quality.
Data Source
AI summary
An unbalanced linear power amplifier (PA) is disclosed having a quadrature coupler with a 90° phase input port, a 0° phase input port, an output termination port, and a signal output port. Each of the 90° phase input port, the 0° phase input port, the output termination port, and the signal output port have a characteristic resistance (Ro). Also included is a first PA having an output coupled to a 90° phase input port of the quadrature coupler and a second PA having an output coupled to a 0° phase input port of the quadrature coupler. Biasing circuitry provides the first PA and the second PA with a similar gain. A tuning network is coupled between the output termination port and ground. The tuning network has an isolation resistance in series with an isolation inductance, wherein the isolation resistance is between about 0.02*Ro Ω and 0.8*Ro Ω.