Parallel Doherty Amplifier Layout for Wider-Band Impedance Matching
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Solution Overview
Problem
Doherty amplifiers face challenges in operating over a broader band due to the frequency sensitivity of λ/4 phase lines, which complicates impedance matching and layout, especially when using high-power FETs like GaN, leading to difficulties in achieving desired characteristics and efficient operation across varying frequencies.
Innovation Solution
The Doherty amplifier is configured with multiple Doherty circuits connected in parallel, each with a carrier amplifier, peaking amplifier, and a combiner that includes λ/4 phase lines with higher characteristic impedance, allowing for impedance transformation and phase compensation, along with matching circuits to relocate frequency-sensitive components closer to the amplifiers, thereby broadening the operational band and downsizing the λ/4 phase lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If λ/4 phase lines with lower characteristic impedance are used, then impedance matching is easier, but the length and area of the phase lines increase
Solution Approach 1:
The patent changes the characteristic impedance parameter of the λ/4 phase lines from conventional lower values to higher values (e.g., 50Ω or higher). This parameter change allows the phase lines to be shortened while still achieving the required impedance transformation function, thereby reducing the overall amplifier size without sacrificing matching performance
Solution Approach 2:
The patent transitions from using long λ/4 phase lines (one-dimensional extension) to compact high-impedance phase lines that achieve the same function in a reduced space. This dimensional compression is achieved by changing the impedance characteristic, allowing the same electrical length to be achieved in a physically shorter distance
2Ease of manufacture
If λ/4 phase lines are placed far from amplifiers, then layout is simpler, but frequency sensitivity increases
Solution Approach 1:
By changing the characteristic impedance parameter to higher values, the patent reduces the physical length of the λ/4 phase lines. This reduction in length inherently decreases the frequency sensitivity of the phase lines, as shorter transmission lines have less phase variation with frequency changes, thereby improving reliability across the operating band
Solution Approach 2:
The patent achieves compact placement of λ/4 phase lines close to the amplifier devices by using high characteristic impedance. This allows the phase lines to be positioned in the immediate vicinity of the amplifiers without requiring extensive layout space, thus reducing frequency sensitivity while maintaining layout simplicity
3Adaptability or versatility
If multiple Doherty circuits are connected in parallel, then operational bandwidth increases, but device complexity increases
Solution Approach 1:
The patent divides the amplifier system into multiple parallel Doherty circuits, each handling a portion of the total power and frequency range. This segmentation allows each individual circuit to be optimized for specific conditions while the parallel combination achieves broader overall bandwidth and higher power capability
Solution Approach 2:
The patent designs the multiple Doherty circuits with identical or similar structures that can operate across overlapping frequency ranges. This multi-functionality allows the parallel configuration to achieve broad bandwidth coverage while maintaining design simplicity and ease of manufacturing through standardization
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
This configuration enhances the Doherty amplifier's ability to maintain high drain efficiency across a wider range of output powers and frequencies, improving its operational bandwidth while reducing the size and complexity of the λ/4 phase lines, making it more suitable for digital modulation signals.
Implementation Method 1
a combiner that transforms an output impedance of the carrier amplifier and combines outputs of the carrier amplifier and the peaking amplifier
Implementation Method 2
a combiner that includes λ/4 phase lines with higher characteristic impedance, allowing for impedance transformation and phase compensation
Data Source
AI summary
A Doherty amplifier includes: an input distributor; a coupler; a plurality of Doherty circuit connected between the input distributor and the coupler; wherein each of Doherty circuits has a carrier amplifier, a peaking amplifier, a distributor distributing a input signal to the carrier amplifier and the peaking amplifier, and a combiner that transforms an output impedance of the carrier amplifier and combines outputs of the carrier amplifier and the peaking amplifier.