Inductively-coupled RF power source

• US 7,940,008 B2
• Filed: 11/06/2008
• Issued: 05/10/2011
• Est. Priority Date: 11/21/2005
• Status: Active Grant

• Current Assignee: Thermo Electron Manufacturing Limited (Thermo Fisher Scientific Incorporated)
• Original Assignee: Thermo Fisher Scientific Incorporated
• Inventors: Fletcher, Roger, Mattaboni, Paul J., Mellor, Robert
• Primary Examiner(s): Choi; Jacob Y
• Assistant Examiner(s): Vu; Jimmy T
• Application Number:
  US12/265,870
• Publication Number:
  US 20090058304A1
• Time in Patent Office: 915 Days
• Field of Search: 324/76.53, 324/76.58, 324/600, 324/622, 324/633, 324/771, 315/111.21, 315/111.01, 315/111.71
• US Class Current: 315/111.21
• CPC Class Codes: G01N 21/73 using plasma burners or torches
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H03L 5/02 of power
• CPC Class Codes: H03L 7/06 using a reference signal applied to a frequency- or phase-locked loop
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence

Abstract

A system and method are disclosed for implementing a power source including a power amplifier that generates a radio-frequency power signal with an adjustable operating frequency. The power amplifier also generates a reference phase signal that is derived from the radio-frequency power signal. An impedance match provides the radio-frequency power signal to a plasma coil that has a variable resonance condition. A phase probe is positioned adjacent to the plasma coil to generate a coil phase signal corresponding to the adjustable operating frequency. A phase-locked loop then generates an RF drive signal that is based upon a phase relationship between the reference phase signal and the coil phase signal. The phase-locked loop provides the RF drive signal to the power amplifier to control the adjustable operating frequency, so that the adjustable operating frequency then tracks the variable resonance condition.

Claims

1. A system for implementing a power source, comprising:

a power amplifier that generates a radio-frequency power signal with an adjustable operating frequency;

an impedance match that provides said radio-frequency power signal to a plasma coil that has a variable resonance condition;

a phase-locked loop device that generates a drive signal to said power amplifier to control said adjustable operating frequency;

a first power control loop including a variable power supply for supplying power to the power amplifier and a power supply controller for monitoring the power supplied to the power amplifier and controlling the variable power supply in response thereto to supply a desired power to the power amplifier; and

a second control loop including a phase probe positioned adjacent to said plasma coil to generate a coil phase signal corresponding to said adjustable operating frequency;

wherein the power amplifier also generates a reference phase signal derived from said radio-frequency power signal; and

wherein the drive signal generated by the phase-locked loop device is based upon a phase relationship between said reference phase signal and said coil phase signal, said adjustable operating frequency then tracking said variable resonance condition to provide substantially stable power transfer from the power amplifier to the plasma coil.

2. The system of claim 1 wherein a phase detector of said phase-locked loop device receives and compares said reference phase signal and said coil phase signal to determine said phase relationship.

3. The system of claim 2 wherein said phase detector generates an error voltage that represents a magnitude and a polarity of said phase relationship.

4. The system of claim 3 wherein said error voltage is equal to zero volts if said adjustable operating frequency is equal to said variable resonance condition.

5. The system of claim 4 wherein said reference phase signal and said coil phase signal are sampled so that said phase relationship is ninety degrees out-of-phase when said error voltage is equal to zero volts.

6. The system of claim 3 wherein said phase detector adjusts said error voltage so that said adjustable operating frequency is set to a resonance slope frequency that is different from a peak resonance frequency of said plasma coil.

7. The system of claim 3 wherein an integrator device performs a filtering process upon said error voltage to remove unwanted radio-frequency components.

8. The system of claim 3 wherein a voltage-controller oscillator of said phase-locked loop device generates said drive signal at said adjustable operating frequency in response to an amplitude and a polarity of said error voltage.

9. The system of claim 1 wherein said power amplifier is operated in a Class E mode to limit power consumption requirements.

10. The system of claim 1 wherein said power amplifier of said power source is directly close-coupled to said impedance match.

11. The system of claim 1 wherein said impedance match has dynamic variable impedance characteristics with respect to said power amplifier.

12. The system of claim 1 wherein said impedance match is implemented with fixed non-adjustable electronic components.

13. The system of claim 1 wherein said impedance match transfers said radio-frequency power signal from said power amplifier to said plasma coil in a balanced manner, said impedance match including a radio-frequency transformer with a grounded center tap.

14. The system of claim 1 wherein said impedance match transfers said radio-frequency power signal from said power amplifier to said plasma coil in an unbalanced manner, said impedance match including a radio-frequency transformer with an ungrounded center tap.

15. The system of claim 1 wherein said plasma coil of said power source is utilized to initiate and sustain a test sample in a plasma state within a plasma torch for analysis with at least one of an optical emission measurement technique and a mass spectrometry measurement technique.

16. The system of claim 1 further comprising a controller device of said power source, said controller device monitoring a plasma status of a test sample being analyzed, said controller device also monitoring a temperature parameter from a heat sensor in said power source.

17. The system of claim 1 wherein said impedance match is implemented with temperature stabilization provided by an adjacent cooling mechanism.

18. The system of claim 1 wherein said power source includes a host interface to permit bi-directional communications between said power source and an external host device.

19. The system of claim 1 wherein said power source is implemented as a self-contained modular device to facilitate incorporating said power source into a host analytical instrument without modifications.

20. The system of claim 1 wherein said power amplifier is operated in a class B mode to reduce an efficiency of power generation for sustaining a low-power plasma operation.

21. A method for implementing a power source, comprising:

generating a radio-frequency power signal with an adjustable operating frequency by utilizing a power amplifier;

utilizing an impedance match to provide said radio-frequency power signal to a plasma coil that has a variable resonance condition; and

generating a drive signal to said power amplifier from a phase-locked loop device to control said adjustable operating frequency;

operating a first power control loop, by;

supplying power to the power amplifier from a variable power supply; and

using a power supply controller to monitor the power supplied to the power amplifier and control the variable power supply in response thereto to supply a desired power to the power amplifier; and

operating a second control loop, by;

generating a reference phase signal derived from said radio-frequency power signal from the power amplifier;

positioning a phase probe adjacent to said plasma coil to generate a coil phase signal corresponding to said adjustable operating frequency; and

generating the drive signal to said power amplifier based upon a phase relationship between said reference phase signal and said coil phase signal, said adjustable operating frequency then tracking said variable resonance condition to provide substantially stable power transfer from the power amplifier to the plasma coil.