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Impedance Change Detector

IP.com Disclosure Number: IPCOM000074526D
Original Publication Date: 1971-May-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Jaeckel, K: AUTHOR

Abstract

The impedance of a glow discharge as encountered in RF sputtering systems is not a constant. This detector circuit provides a DC error voltage corresponding to load impedance deviations from the matched condition, e.g. load and line impedances are equal. After proper amplification, the error signal can be used to control motorized matching network components which compensate for any impedance changes.

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Impedance Change Detector

The impedance of a glow discharge as encountered in RF sputtering systems is not a constant. This detector circuit provides a DC error voltage corresponding to load impedance deviations from the matched condition, e.g. load and line impedances are equal. After proper amplification, the error signal can be used to control motorized matching network components which compensate for any impedance changes.

A thin sense wire 1, one inch long, is placed parallel to and halfway in between inner and outer conductors 2 and 3 of coaxial transmission line.

Voltage vc is proportional to v1 and is coupled to sense wire 1 through capacitance Co between wire 1 and inner line conductor 2. Diode CR1 clamps sense wire 1 to ground for all positive half-cycles and therefore assumes a negative DC potential with respect to ground. This potential is equal to Vc which is half the peak-to-peak value of vc. Choke L1 connects this voltage to both C1 and C2. Capacitor C2 receives an additional charge due to voltage vAB which is induced by the line current il between points A and B on wire 1.

Diode CR2 rectifies v:AB to VAB the half peak-to-peak value. Total voltage across C2 is then Vc + VAB. Both capacitors C1 and C2 discharge as indicated by currents I1 and I2 through balancing potentiometer 4.

When the load and line impedances are matched, the detector output VD is zeroed with balancing potentiometer 5. Any load impedance change will produce variations in v1 and...