| 摘要 |
PROBLEM TO BE SOLVED: To prevent matching deviation by adjusting the capacity of a matching variable capacitor and a tuning variable capacitor in accordance with impedance obtained in a detection circuit and the phases of the voltage and current of an input high frequency and so as to prevent matching operation, based on radiation power detected when high frequency output rises. SOLUTION: A detection circuit 20 obtains impedance and phase difference, based on high frequency voltage and current in an arithmetic circuits 21 and converts them into DC signals Vz Vθin conversion circuit 22A and 22B. Comparison amplifiers 8 and 10 adjust a matching variable capacitor 4 and a tuning variable capacitor 5 by motors 9 and 11 based on the DC signals Vz and Vθ. Although the high-frequency output of a high-frequency oscillator 1 repeats on/off by a pulse signal from a modulation signal generation circuit 12 and large reflected power is generated in the rise period of high frequency output, the conversion circuits 22A and 22B make the DC signals Vz and Vθto '0' in a reflection power generating period.
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