Variable Impedance Matching Circuit for RF CO2 Lasers

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Solution Overview

Problem

Existing impedance matching circuits for RFPS in CO2 gas discharge lasers are not easily adjustable to compensate for impedance variations between lasers of the same model, leading to inefficiencies in power transfer and manufacturing challenges.

Innovation Solution

A variable impedance matching circuit using two transmission-line sections, each with an electrical length of less than one-twelfth of a wavelength, and a selectively variable electrical component at the node between them, allowing for adjustment of impedance and phase to match varying load impedances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a fixed impedance matching circuit is used, then the circuit structure is simple, but it cannot compensate for impedance variations between lasers of the same model

Engineering Contradiction:

Improveimpedance matching adaptabilityVSAvoidcircuit structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies the dynamics principle by making the electrical component (capacitor or inductor) selectively variable rather than fixed. This allows the impedance matching circuit to adapt to different load impedances by changing the electrical characteristic of the variable component, thereby resolving the contradiction between adaptability and complexity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies parameter changes by selectively varying the electrical characteristic (capacitance or inductance) of the electrical component to match different load impedances. This allows a single circuit topology to handle multiple impedance conditions without requiring multiple fixed circuits, thus improving adaptability while maintaining relatively simple structure.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If discrete LC networks are used for impedance matching, then the matching can be adjusted, but the components are too large for modern solid-state RFPS packaging

Engineering Contradiction:

Improveimpedance matching capabilityVSAvoidcomponent size

Core Design Contradiction:

Adaptability or versatilityVSVolume of moving object

Solution Approach 1:

The patent applies mechanics substitution by replacing discrete mechanical LC components with integrated transmission line structures. The transmission lines provide the necessary inductive and capacitive effects through their distributed parameters, eliminating the need for large discrete components and enabling compatibility with modern solid-state RFPS packaging.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent applies segmentation by dividing the impedance matching function into multiple transmission line sections (first and second transmission lines with different characteristic impedances) rather than using single discrete components. This distributed approach achieves the desired impedance transformation while maintaining compact dimensions suitable for integrated packaging.

Inventive Principle:

Principle #1Segmentation

3Ease of operation

If fractional wavelength transmission lines are used, then impedance matching is achieved, but the transmission lines are too long for compact packaging

Engineering Contradiction:

Improveimpedance matching performanceVSAvoidtransmission line length

Core Design Contradiction:

Ease of operationVSLength of stationary object

Solution Approach 1:

The patent applies dynamics by using a selectively variable electrical component in conjunction with short transmission lines. This combination allows the system to achieve impedance matching across a range of conditions without requiring long fixed-length transmission lines, thereby improving ease of operation while reducing physical length.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies preliminary action by pre-configuring the transmission lines with specific characteristic impedances and using a variable electrical component that can be adjusted beforehand to match expected load conditions. This allows compact transmission line lengths to achieve effective impedance matching through proper preliminary configuration of the electrical component.

Inventive Principle:

Principle #10Preliminary action

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

Enables efficient RF power transfer and reduces parts inventory by allowing impedance matching across a range of load impedances, improving manufacturing efficiency and compatibility with modern solid-state RFPS packaging.

Implementation Method 1

introduces a phase-shift of 90° (π/2 radians) between the output of the RFPS and the input to the discharge electrodes

Methodology Applied

Scientific EffectPhase-shift:

Implementation Method 2

For optimum impedance matching, λ/4 transmission line 14 has a characteristic impedance of 57 Ohms, i.e., (RS*RL)1/2

Methodology Applied

Scientific EffectImpedance transformation:

Data Source

PatentUS8354893B2Impedance-matching transformers for RF driven CO2 gas discharge lasers

Publication Date: 2013.01.15 COHERENT INC

AI summary

In a CO2 gas discharge laser energized by a radio frequency (RF) power source a transformer having selectively variable output impedance is used to match output impedance of the power source to the impedance of discharge electrodes of the laser. A similar transformer can be used to impose a selective variable phase-shift on the RF power from the source. The variable impedance transformer can also be used for impedance matching between amplifier stages in the power source.