ABSTIMMVERFAHREN UND -EINRICHTUNG FUER KAPAZITAETSMESSBRUECKEN

摘要

For detecting small variations in capacitance in a specimen 3 under test, a HF generator 1 supplies HF current through a quadruple balun transformer 2 to a parallel resonant circuit including the specimen 3, a capacitance diode 5 and an inductor 7, and a pre-amplifier 9 is connected to a phase sensitive rectifier (not shown) to produce an output representing capacitance variation of the specimen 3. Bias voltages U1, U2 are applied to the specimen 3 and the capacitor 5 and a compensating HF current is applied to the pre-amplifier 9 with 180 DEG phase shift via FET 8 controlled by a voltage U3. A gate 11 under the control of U4 switches the input of pre-amplifier 9 to compensate for relaxation time effects of the specimen 3. Balance of the apparatus is achieved by firstly applying a control voltage U4 to FET 11 to reduce the gain of pre-amplifier 9. Control voltage U5 is then adjusted to achieve balance. <IMAGE>