Planar Balun Transformer for High-Power RF Combining
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Solution Overview
Problem
High-power applications, such as MRI systems, require efficient power combining and dividing, but existing technologies necessitate additional components, leading to increased losses and costs, especially at high power levels.
Innovation Solution
A planar balun topology with inductively coupled unbalanced and balanced coils, along with an auxiliary coil, arranged in parallel planes on a printed circuit board, allowing for reduced component count and improved impedance transformation, enabling efficient power combining and dividing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional power combining techniques (Wilkinson, Gysel or Radial) are applied to increase total system power, then power output is improved, but device complexity and loss increase due to additional components
Solution Approach 1:
The patent combines the balun transformer and power combiner functions into a single integrated structure. The balanced coil serves dual purposes: as part of the balun transformer for impedance transformation and as the power combining network. This eliminates the need for separate power combiner components while achieving the same power combining effect, thereby reducing device complexity and component count.
Solution Approach 2:
The balanced coil in the invention performs multiple functions simultaneously: it acts as the secondary winding of the balun transformer for impedance transformation, and also serves as the power combining network. This multi-functionality reduces the overall component count and simplifies the device structure while maintaining the ability to combine power from multiple sources.
2Power
If traditional power combining techniques are applied to increase total system power, then power output is improved, but loss increases due to additional components
Solution Approach 1:
By merging the balun transformer and power combiner into a single integrated structure, the patent eliminates the interfaces and connections between separate components that would introduce additional losses. The direct inductive coupling between the unbalanced coil and balanced coil provides efficient power transfer while the integrated power combining function reduces resistive losses associated with separate combiner components.
3Ease of operation
If co-axial cable transmission line balun is used to convert balanced signal to un-balanced signal in push-pull configuration, then impedance matching is improved, but device complexity increases
Solution Approach 1:
The patent replaces the traditional co-axial cable transmission line balun with a planar printed circuit board implementation using inductively coupled coils. The unbalanced coil and balanced coil provide the same impedance transformation function through magnetic coupling, eliminating the need for co-axial cables and mechanical connectors, thereby reducing device complexity while maintaining impedance matching performance.
Solution Approach 2:
The invention transitions from a three-dimensional co-axial cable structure to a two-dimensional planar printed circuit board layout. The coils are printed on the PCB and utilize magnetic coupling through the board thickness, providing the same balun function in a flattened, integrated structure that reduces overall device complexity and allows for easier integration with other planar 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
The solution reduces the number of additional components required for power combining or dividing, enhances manufacturing quality, and supports high-power applications with improved impedance transformation and efficiency, particularly suitable for LDMOS transistors, achieving power ratings up to 5 kW.
Implementation Method 1
The unbalanced coil and the balanced coil are inductively coupled and electrically isolated from each other
Implementation Method 2
The at least one auxiliary coil is inductively coupled to the balanced coil and extends between a second single-ended signal terminal and a second reference forming an unbalanced combiner-divider
Data Source
AI summary
A radiofrequency power amplifier includes a balun transformer and a plurality of power transistor pairs arranged in a push-pull configuration. The balun transformer has an unbalanced coil extending between a first single-ended signal terminal and a first reference, and a balanced coil extending between a first balanced signal terminal and a second balanced signal terminal. The balun transformer also includes an auxiliary coil electrically isolated from the unbalanced coil and the balanced coil. The auxiliary coil is inductively coupled to the unbalanced coil and extends between a third balanced signal terminal and a fourth balanced signal terminal forming a balanced combiner-divider. An output of a first one of the power transistor pairs is coupled to the first and second balanced signal terminals and an output of a second one of the power transistor pairs is coupled to the third and fourth balanced signal terminals.