Power Amplifier Output Combining With Upward Impedance Matching
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Solution Overview
Problem
Existing power amplifiers face challenges in achieving large output power due to high impedance at power cell ports, significant footprint, and high losses in Wilkinson and transformer-based combiners, as well as difficulties in matching small Ropt for transistors in distributed amplifiers.
Innovation Solution
A power amplifier design that combines output powers of multiple power cells through series-connected transmission lines with upward impedance transformation networks, such as tapped capacitors or inductors, to match small Ropt and deliver large output power, reducing impedance and parasitic capacitance loading on transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If Wilkinson power combiner is used to combine output powers from multiple power cells, then constructive power combining is achieved, but the combiner presents high impedance for each power cell and occupies large footprint
Solution Approach 1:
The power combiner is segmented into multiple transmission line segments with progressively changing characteristic impedances. Instead of using a single Wilkinson combiner structure, the invention divides the combining function across multiple sections, each with optimized impedance values that decrease from the power cell side toward the output side, thereby reducing the overall footprint while maintaining power combining efficiency
Solution Approach 2:
Each transmission line segment is designed with locally optimized characteristic impedance values that vary along the signal path. The impedance is highest at the power cell input and progressively decreases toward the output, creating local impedance conditions that minimize the footprint of each segment while collectively achieving the desired power combining function
2Power
If transformer-based power combining is used, then power combining is achieved, but significant losses occur due to winding resistance and coupling losses
Solution Approach 1:
The mechanical transformer structure with windings and magnetic cores is replaced with an electrical transmission line-based combining network. This substitution eliminates the inherent losses associated with winding resistance, skin effect, and magnetic core losses, achieving power combining through distributed electrical fields in transmission lines instead of concentrated magnetic fields in transformers
3Loss of energy
If distributed amplifier with transmission lines is used to combine output powers, then losses are reduced compared to transformers, but the transistors experience unequal power distribution and suboptimal loading
Solution Approach 1:
Each transistor in the distributed amplifier is provided with locally optimized impedance transformation networks that tailor the load impedance seen by each device. This local optimization ensures that each transistor operates at its optimal load impedance for maximum power delivery, rather than experiencing the unequal and suboptimal loading that occurs in conventional distributed amplifiers
Solution Approach 2:
The characteristic impedances of the transmission line segments are carefully selected and varied to achieve optimal power distribution. By changing the impedance parameters along the signal path and at each power cell output, the invention ensures that each transistor delivers its maximum available power while maintaining proper loading conditions
4Area of moving object
If short micro strip transmission lines are used to minimize combiner footprint, then footprint is reduced, but the combiner presents high impedance (>50Ω) for each power cell
Solution Approach 1:
Impedance transformation networks are inserted at each power cell output to provide local impedance matching. These networks transform the high impedance (>50Ω) presented by the short transmission line combiner back down to the standard 50Ω system impedance, enabling proper impedance matching without requiring long transmission lines and thereby maintaining the compact footprint
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 provides low impedance for each power cell, reduces losses, and minimizes footprint, enabling efficient delivery of large output power while matching small Ropt for transistors, thus enhancing power combining efficiency and output power capabilities.
Implementation Method 1
a number n of output transmission lines TL1i for combining output powers from the power cells
Implementation Method 2
Each impedance transformation network is an upward impedance transformation network for transforming an output impedance of each power cell at the input terminal of the impedance transformation network into a higher impedance at the output terminal of the impedance transformation network
Data Source
AI summary
A power amplifier has a number n of power cells Ai, a number n of output transmission lines TL1i for combining output powers from the power cells, and a number n of impedance transformation network ITNi, where i=1, . . . n. The number n of output transmission lines are connected in series. The output terminal of each power cells is connected to its output transmission line via its impedance transformation network. Each impedance transformation network is an upward impedance transformation network for transforming an output impedance of each power cell at the input terminal of the impedance transformation network into a higher impedance at the output terminal of the impedance transformation network. A number n of input transmission lines TL0i (i=1, 2 . . . n)=connected in series. The input terminal of the i-th power cell is connected to the second terminal of the i-th transmission line via a capacitor, where i=1, . . . n.