Doherty Amplifier Stub Matching for Wideband Compact Circuits
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Doherty amplifiers face an increase in circuit size due to the need for a load modulation line with an electrical length of 90 degrees, a frequency compensation line with an integral multiple of 180 degrees, and an input phase adjustment line with a specific electrical length difference, which limits their bandwidth without corresponding increases in circuit size.
Innovation Solution
A Doherty amplifier configuration that includes a transmission line with an electrical length of less than 90 degrees, a capacitive and inductive stub connected in parallel to the peak amplifier, and an output matching circuit that transforms impedance, allowing for Doherty operation with reduced overall circuit size by using a transmission line with an electrical length of 90 degrees for the carrier and peak amplifiers and an open or short stub to compensate for frequency dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a load modulation line with electrical length of 90 degrees, frequency compensation line with integral multiple of 180 degrees, and input phase adjustment line with specific electrical length difference are used, then broadband matching is achieved, but circuit size increases
Solution Approach 1:
The patent changes the electrical length parameter of the transmission line from the conventional 90 degrees to less than 90 degrees (specifically 45 degrees). This parameter modification allows the circuit to achieve broadband matching performance while reducing the physical size of the transmission lines and overall circuit configuration.
Solution Approach 2:
The patent introduces a stub structure connected in parallel to the peak amplifier output, which provides an additional degree of freedom for impedance matching. This stub can be adjusted independently to compensate for frequency dependence, enabling broadband operation without proportionally increasing the main transmission line lengths.
2Length of stationary object
If transmission line with electrical length of less than 90 degrees is used, then circuit size is reduced, but achieving Doherty operation with proper impedance transformation becomes more difficult
Solution Approach 1:
The stub acts as an intermediary element that facilitates impedance matching between the peak amplifier and the load. By adjusting the stub's electrical length and characteristic impedance, the circuit achieves proper impedance transformation despite using shorter transmission lines, thereby simplifying the overall design while maintaining performance.
Solution Approach 2:
The transmission line with electrical length of less than 90 degrees serves multiple functions: it provides the necessary phase shift for Doherty operation, contributes to impedance transformation, and when combined with the stub, enables broadband matching. This multi-functionality reduces the need for separate dedicated components.
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 broadens the bandwidth of Doherty operation without increasing circuit size, achieving wideband matching during both back-off and saturation by compensating for frequency dependence with the open or short stub, thereby enhancing the amplifier's performance.
Implementation Method 1
a stub that is connected in parallel to the output terminal of the transistor for the peak amplifier and that is capacitive and inductive in a working frequency band
Implementation Method 2
an output matching circuit connected to the output terminal of the transistor for the peak amplifier and the transmission line at an output combination point, and an output load, the output matching circuit to transform an impedance of the output load into an impedance, as viewed from the output combination point, lower than the impedance of the output load
Implementation Method 3
an input phase adjustment line that is a line that adjusts a phase of a signal input to the transistor for the peak amplifier with respect to the transistor for the carrier amplifier
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A conventional Doherty amplifier requires a load modulation line having an electrical length of 90 degrees, a frequency compensation line having an electrical length of an integral (n) multiple of 180 degrees, and an input phase adjustment line having an electrical length corresponding to a difference (180° × n - 90°) between the electrical length of the load modulation line and the electrical length of the frequency compensation line. Thus, the conventional Doherty amplifier has a problem of an increase in circuit size . A Doherty amplifier according to the present invention includes: a transistor for a carrier amplifier; a transistor for a peak amplifier; a transmission line connected between an output terminal of the transistor for the carrier amplifier and an output terminal of the transistor for the peak amplifier; a stub that is connected in parallel to the output terminal of the transistor for the peak amplifier and that is capacitive and inductive in a working frequency band; and an output matching circuit connected to the output terminal of the transistor for the peak amplifier, the transmission line, and an output load, the output matching circuit to transform an impedance of the output load into an impedance lower than the impedance of the output load.