Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
1996-12-31
2001-12-11
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C315S224000, C315S223000, C219S121480, C331S176000
Reexamination Certificate
active
06329757
ABSTRACT:
This invention relates to electronic oscillator circuits, particularly to such circuits driven by transistors, and more particularly to such circuits having a loading such as an induction coupled plasma generator.
BACKGROUND
High frequency electronic oscillators, broadly in the range of 10 to 100 MHz, are used for a variety of purposes ranging from radio transmission and reception to heating of materials. A particular application is for the formation of a plasma discharge with an apparatus known as an induction coupled plasma (ICP) generator. Such plasma systems typically are used for spectroscopy, treatment of fine powders, melting of materials, chemical reactions and the like. These applications derive from the high temperatures inherently associated with a plasma, which are high enough to effect electron excitation and ionization of the plasma gas and injected materials. Plasma generation also is utilized to produce ions utilized in instruments for mass spectroscopy and, at low pressure, for vapor deposition processes. Other applications are associated with induction heating of materials, such as graphite of an induction furnace, melting of metals, and the like.
Oscillators must be capable of generating sufficient power for the application, i.e. approximately one kilowatt for ICP. Generally this has been accomplished with circuits incorporating vacuum tubes. Typical tube oscillators in current use with ICP are shown in U.S. Pat. Nos. 4,629,940 and 4,818,916, and copending patent application Ser. No. 08/079,963 filed Jun. 18, 1993 now abandoned and its counterpart European patent application publication No. 0 568 920 A 1, all commonly owned by the present assignee. Other conventional tube oscillators, some of which may not necessarily be suitable for induction heating, are taught in standard texts on the subject. Tube oscillators in common use for ICP tend to be cumbersome, sensitive to tuning problems and limited in efficiency of power transfer (up to about 50%). Tuning problems are associated with requirements for alignment of impedance matching networks, and with the coupling with the ICP and the variable transfer of power thereto. Tubes tend to have changing characteristics with time. Tube circuits also require periodic replacement of tubes, due to finite lifetime of the thermionic emission of the filament electron source.
Oscillators based on transistors have been known for applications such as radio, audio and the like but, to the knowledge of the present inventors, the configurations described herein have not been used for plasma generation. Examples of transistor oscillators are taught in a publication “High Frequency Circuit Design” by J. K. Hardy, 246-252(Prentice-Hall 1979). These generally deliver low power and use parallel oscillator circuits.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel high frequency oscillator system. Another object is to provide such a system utilizing one or more transistors in place of vacuum tubes. A further object is to provide such a transistor system utilizing a series oscillator circuit. Yet another object is to provide such a transistor system having a reduction in problems and complexities associated with tube oscillators. Other objects are to provide such a system capable of delivering relatively high power, and to provide such a system adapted to an induction plasma generator.
The foregoing and other objects are achieved, at least in part, by a high frequency oscillator system formed of a series oscillator circuit comprising an inductance coil, a capacitance means cooperative with the coil to support a high frequency oscillation in the circuit, and a transistor for driving the oscillation. The capacitance means is connected in series with the coil between the drain and source terminals of the transistor. A DC primary voltage is applied between the drain terminal and the source terminal so as to supply electrical power to the transistor means and thereby to the oscillator circuit. A feedback means responsive to the oscillation frequency is connected to the gate terminal to effect a positive feedback for the transistor means to drive the oscillation. The feedback may be capacitive or inductive. In an embodiment with capacitive feedback, the capacitance means comprises a primary capacitance connected in series with the load coil between the drain and an intermediate point connected to the transistor gate terminal, and a secondary capacitance connected between the intermediate point and the source terminal.
In another embodiment a high frequency oscillator system is formed of a series oscillator circuit comprising a first section of circuit, a second section of circuit, and an inductance coil connecting between the first section and the second section. The first section comprises a first capacitance means and a first transistor, and the second section comprises a second capacitance means and a second transistor. The first section, the second section and the coil are operatively connected to support an oscillation in the oscillator circuit. The first transistor has a first source terminal, a first drain terminal and a first gate terminal. The second transistor has a second source terminal, a second drain terminal and a second gate terminal. The first capacitance means comprises a first primary capacitance connected between the coil and the first drain terminal, and the second capacitance means comprising a second primary capacitance connected between the coil and the second drain terminal. A DC primary voltage is applied between the first drain terminal and the first source terminal, and between the second drain terminal and the second source terminal, so as to supply electrical power to each transistor and thereby to the oscillator circuit. A first feedback means responsive to the oscillation is connected to the first gate terminal to effect a positive feedback for the first transistor means to drive the oscillation. A second feedback means responsive to the oscillation is connected to the second gate terminal to effect a positive feedback for the second transistor means to further drive the oscillation.
For capacitive feedback in this system, the first feedback means comprises a first capacitive connection between the second section and the first gate terminal, and the second feedback means comprises a second capacitive connection between the first section and the second gate terminal. For inductive feedback the first feedback means comprises a first inductive connection between the first section and the first gate terminal, and the second feedback means comprises a second inductive connection between the second section and the second gate terminal.
Both single and dual transistor circuits are advantageously applicable to a load means that is inductively receptive of high frequency electrical power for utilization thereof. The inductance coil then is a load coil encompassing the load means so as to inductively couple therewith, whereby electrical power in the oscillation loop is transferred inductively through the load coil to the load means. A particular system is a plasma generating system, wherein the load means comprises a channeling means for channeling a plasma-forming gas within the coil. Electrical power in the oscillation loop is transferred inductively through the load coil to the plasma-forming gas to effect a plasma in the channeling means.
REFERENCES:
patent: 3134947 (1964-05-01), Charasz
patent: 4577165 (1986-03-01), Uehara et al.
patent: 4629940 (1986-12-01), Gagne et al.
patent: 4818916 (1989-04-01), Morrisroe
patent: 4935596 (1990-06-01), Gagne
patent: 5334834 (1994-08-01), Ito et al.
patent: 3429574 (1986-02-01), None
patent: 4119738 (1992-12-01), None
patent: 0568920 (1996-03-01), None
“High Frequency Circuit Design” by James K. Hardy, pp. 246-252 (Prentice Hall 1979).
Gagne Peter H.
Morrisroe Peter J.
Philogene Haissa
St. Onge Steward Johnston & Reens LLC
The Perkin-Elmer Corporation
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