Inverted Doherty Amplifier Topology for Broadband RF Bandwidth
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Solution Overview
Problem
Conventional Doherty amplifiers face bandwidth limitations due to the long electrical path length introduced by impedance-matching components, which restrict their RF fractional bandwidth, making them unsuitable for future broadband RF communication systems.
Innovation Solution
The design of an inverted Doherty amplifier configuration, where an impedance inverter is placed between the combining node and the peaking amplifier, and optimized impedance-matching components and impedance values are used to enhance bandwidth, allowing for a 90° phase delay at the coupler and odd multiple phase shifts in the impedance inverter, resulting in significantly larger RF fractional bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional impedance-matching components are used in Doherty amplifier, then power transfer is achieved, but RF fractional bandwidth is limited to below 4%
Solution Approach 1:
The patent inverts the conventional Doherty amplifier topology by placing the impedance inverter between the combining node and the peaking amplifier output, rather than between the main amplifier output and the combining node. This inversion reconfigures the signal flow and impedance transformation paths, enabling broader bandwidth operation by equalizing the electrical path lengths experienced by signals from both amplifiers across a wider frequency range.
Solution Approach 2:
The patent changes the impedance parameters and phase delay characteristics of the inverter and coupling components. Specifically, it uses an inverter with odd multiple phase shifts (90°, 270°, etc.) and optimizes impedance values to achieve broadband matching. This parameter optimization allows the amplifier to maintain proper impedance transformation and phase relationships across frequencies exceeding 20% fractional bandwidth.
2Power
If long electrical path length is introduced by impedance-matching components, then power amplification is achieved, but RF fractional bandwidth is restricted
Solution Approach 1:
By inverting the topology and repositioning the impedance inverter, the patent achieves power amplification through an alternative signal path configuration that maintains proper phase and impedance relationships without requiring long electrical paths, thereby enabling broadband operation.
Solution Approach 2:
The inverted configuration creates an asymmetric arrangement of components that balances the electrical path lengths in a different manner than conventional symmetric Doherty amplifiers. This asymmetric topology allows both amplifiers to contribute effectively across a broader frequency range while maintaining power amplification capability.
3Device complexity
If conventional Doherty amplifier configuration is used, then circuit simplicity is maintained, but bandwidth exceeds 20% cannot be achieved
Solution Approach 1:
The inverted configuration maintains relatively simple circuit topology by using the same basic components (amplifiers, coupler, inverter, impedance-matching components) but rearranging their connections. This topological inversion achieves broadband performance without significantly increasing circuit complexity.
Data Source
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AI summary
Apparatus and methods for an inverted Doherty amplifier operating at gigahertz frequencies are described. RF fractional bandwidth and signal bandwidth may be increased over a conventional Doherty amplifier configuration when impedance- matching components and an impedance inverter in an output network of the inverted Doherty amplifier are designed based on characteristics of the main and peaking amplifier and asymmetry factor of the amplifier.