Multiband Doherty Amplifier With Cascaded Impedance Conversion
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Solution Overview
Problem
Conventional Doherty amplifiers are limited to operating efficiently at a single designated frequency band due to the frequency-dependent impedance conversion performed by the ¼-wave transmission line, leading to suboptimal performance and reduced gain and efficiency at other frequency bands.
Innovation Solution
A multiband Doherty amplifier design that includes a divider, a carrier amplifier, a delay element, a multiband impedance converter with N cascade-connected impedance conversion transmission lines, and a combiner with N impedance conversion transmission lines, ensuring equal impedance conversion across multiple frequency bands, allowing the carrier amplifier to operate optimally and maintaining high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single ¼-wave transmission line is used for impedance conversion, then the amplifier operates efficiently at one designated frequency, but performance degrades at other frequency bands
Solution Approach 1:
The single impedance conversion transmission line is segmented into multiple transmission lines with different electrical lengths. Each transmission line is designed to provide optimal impedance conversion at a specific frequency band, allowing the amplifier to maintain high efficiency across multiple frequency bands simultaneously
Solution Approach 2:
The impedance conversion network is designed to perform multiple functions by incorporating transmission lines with different electrical lengths that can handle different frequency bands. This multi-functional design allows a single amplifier circuit to operate efficiently across multiple frequency bands without requiring separate amplifiers for each band
2Productivity
If the transmission line length is optimized for one frequency, then gain and efficiency are maximized at that frequency, but performance drops at other frequencies
Solution Approach 1:
The electrical lengths of the transmission lines are varied to create different impedance transformation characteristics for different frequency bands. By changing the electrical length parameter of each transmission line, the system can optimize performance for multiple frequencies rather than being constrained to a single design frequency
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 multiband Doherty amplifier achieves sufficient gain and efficiency across multiple frequency bands, with improved drain efficiency and power amplification capabilities compared to conventional Doherty amplifiers, even when the signal frequency differs from the design frequency.
Implementation Method 1
the 1/4-wave transmission line 103 on the output side of the carrier amplifier 102. With this function of the 1/4-wave transmission line 103, a load impedance at the output port of the carrier amplifier 102 changes
Implementation Method 2
a delay element which is connected to the other output port of the divider and delays the other divided signal
Data Source
AI summary
A multiband Doherty amplifier having a configuration including a divider which divides an input signal into two, a carrier amplifier which amplifies one of the divided signals, a delay element which delays the other divided signal, a peak amplifier which amplifies the output signal of the delay element, an impedance converter which is connected to an output port of the carrier amplifier and performs predetermined impedance conversion and a combiner which combines the output signals of the peak amplifier and the impedance converter, wherein the electric length of the delay element is the same as the electric length of the impedance converter and the impedance converter has N (N≧2) cascade-connected impedance conversion transmission lines and performs substantially the same impedance conversion at each of the N frequencies.