Coupled-Line Doherty Power Amplifier for Low-Q Wideband Operation
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Solution Overview
Problem
Conventional Doherty power amplifiers have a narrow bandwidth due to large impedance transformation ratios and complex topologies with phase delays, limiting their usage in wideband applications, particularly in modern wireless communication systems.
Innovation Solution
A wideband Doherty power amplifier design incorporating a coupled phase compensation network with reduced external Q-factor, featuring a main and auxiliary power amplification device, fundamental impedance inverters, and a coupled phase compensation network with transmission line sections and end-connected coupled transmission lines to compensate for phase shifts between the devices, extending the bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional quarter-wavelength transmission line is used for phase compensation, then the structure is simple, but the external Q-factor is high which limits bandwidth
Solution Approach 1:
The phase compensation network is segmented into multiple coupled transmission line sections instead of using a single quarter-wavelength line. This segmentation allows each section to contribute to phase compensation while reducing the overall external Q-factor, thereby extending bandwidth without excessive complexity
Solution Approach 2:
The invention transitions from a one-dimensional single transmission line approach to a two-dimensional coupled transmission line structure. The coupled lines provide additional degrees of freedom for impedance control and phase adjustment, enabling bandwidth extension while maintaining manageable structural complexity
2Power
If peaking branch uses large impedance transformation ratio, then saturation performance is improved, but peaking amplifier bandwidth is restricted
Solution Approach 1:
The impedance transformation is distributed across multiple coupled transmission line sections rather than concentrated in a single element. Each section provides a portion of the total impedance transformation, allowing saturation performance to be achieved while maintaining bandwidth through the distributed approach
Solution Approach 2:
The coupled transmission line structure provides dynamic impedance characteristics that vary with frequency in a controlled manner. This allows the peaking amplifier to maintain good performance across a wider bandwidth while still achieving the required saturation performance through the frequency-dependent impedance transformation
3Ease of manufacture
If conventional FII topology is used, then impedance inversion is achieved, but complicated topology introduces large phase delays
Solution Approach 1:
The impedance inversion function and phase compensation function are merged into a single coupled transmission line structure. This eliminates the need for separate FII components and reduces the cumulative phase delays that would result from multiple discrete elements
Solution Approach 2:
The coupled transmission line sections serve multiple functions simultaneously: they provide impedance inversion, phase compensation, and bandwidth extension. This multi-functionality reduces the overall device complexity by eliminating the need for separate conventional FII topologies and phase compensation networks
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves efficient operation over a significantly wider frequency range, with measured results demonstrating 55% fractional bandwidth and efficiency exceeding 41% from 1.3-2.3 GHz, suitable for 4G and 5G wireless communication systems, reducing electrical power costs.
Implementation Method 1
two pairs of end-connected coupled transmission lines connected in parallel between the first transmission line section and the second transmission line section
Data Source
AI summary
The present invention provides a wideband Doherty power amplifier comprising: a main power amplification device; an auxiliary power amplification device arranged in parallel with the main power amplification device; and a coupled phase compensation network configured for compensating a phase shift between the main power amplification device and the auxiliary power amplification device. The phase compensation network comprising a first transmission line section; a second transmission line section extending substantially collinearly with the first transmission line section; and two pairs of end-connected coupled transmission lines connected in parallel between the first transmission line section and the second transmission line section. The provided Doherty power amplifier demonstrated operation at 6 dB back-off between 1.3-2.3 GHz with efficiency in excess of 41%, which can be used in modern and future wireless communication systems which require power amplifiers operating over a wide frequency range.