Impedance Control Unit Using Re-entrant Coupled Lines
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Solution Overview
Problem
Existing impedance control units in RF amplifiers, such as Doherty amplifiers, face challenges in individually controlling odd mode and even mode impedances, as modifying impedances at higher harmonic frequencies affects both modes simultaneously, complicating amplifier design and making it difficult to achieve optimal impedances for amplifying elements.
Innovation Solution
The use of re-entrant type coupled lines with a locally grounded intermediate plane allows for independent control of even mode and odd mode impedances by creating a capacitor-like effect for even mode signals without significantly altering odd mode behavior, using electrical connections positioned at specific quarter wavelengths based on mode propagation velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If phase delay elements are added between the balun and the output of the amplifying elements to manipulate impedance, then impedance control at various frequencies is improved, but the device complexity increases and the phase velocities difference between even and odd modes causes different effects on each mode
Solution Approach 1:
The patent divides the impedance control function into separate control paths for even mode and odd mode signals. By segmenting the control mechanism, each mode can be independently adjusted without affecting the other, resolving the issue where phase delay elements affect both modes differently due to phase velocity differences.
Solution Approach 2:
The patent introduces an intermediate transformation stage that converts the differential signal into even mode and odd mode components separately, allowing independent impedance control for each mode. This intermediary mechanism enables precise impedance manipulation without the complexity of direct phase delay elements affecting both modes simultaneously.
2Adaptability or versatility
If the coupling coefficient between transmission lines is increased to expand balun bandwidth, then the bandwidth is improved, but the minimum allowable distance between metal structures limits the separation between strips
Solution Approach 1:
The patent transitions from planar coupled lines to three-dimensional folded coupled lines. By folding the transmission lines in the vertical dimension, the coupling coefficient can be increased without reducing the horizontal separation between strips, thus expanding bandwidth while respecting manufacturing constraints on minimum metal structure distances.
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 approach enables precise control of odd and even mode impedances at desired frequencies, improving amplifier performance by allowing optimal impedance settings for amplifying elements, particularly beneficial for classes like Class E and inverse Class F, where harmonic terminations are critical.
Implementation Method 1
The use of re-entrant type coupled lines with a locally grounded intermediate plane allows for independent control of even mode and odd mode impedances by creating a capacitor-like effect for even mode signals
Implementation Method 2
In the radiofrequency (RF) domain, e.g. between 0.1GHz and 100GHz, the balun is often realized with transmission lines that are electromagnetically coupled
Implementation Method 3
It is known that by adding phase delay elements between the balun and the output of the amplifying elements, it is possible to manipulate the impedance seen by the amplifying elements at the various frequencies
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3D
AI summary
The present invention relates to an impedance control unit. The present invention further relates to a balun unit, an electronic device, and a Doherty amplifier, each comprising the impedance control unit. The invention proposes an impedance control unit, comprising a pair of re-entrant type coupled lines, that is characterized in that it comprises an electrical short between the intermediate plane and the ground plane arranged locally inside the pair of coupled lines.