Abstract: A device for measuring the resistivity of a conductive layer buried beneath an outer layer. The device is capacitively coupled to the buried layer by a driven electrode and a pickup electrode. An adjustable frequency source resonates the two electrodes with an inductor so that an attached meter measures the resistivity of only the buried layer.

Abstract: A non-contacting voltage metering device for monitoring the electrical potential of a test surface includes a sensing integrator, and a tuning fork mechanism for modulating the capacitive coupling. The integrator input is coupled to the amplifier output and the integrator output is connected to a high-voltage FET output amplifier. The apparatus includes a feedback circuit with a phase sensitive detector which has an input coupled to the integrator output and an output coupled to the integrator input, and a reference terminal coupled to the modulating mechanism for receiving the predetermined frequency.

Abstract: A voltage amplifier for amplifying an input voltage signal is disclosed. The amplifier includes a string of MOSFET circuits coupled between a voltage-to-current converter and a high voltage power supply terminal. The string of MOSFET circuits may be expanded to achieve linear voltage amplification over a wide voltage range.

Abstract: A circuit for providing DC bootstrapping to an AC amplifier integrates a sample of the output of the amplifier and feeds the result of that integration to the input of the amplifier, thereby driving the input of the amplifier to a zero potential level. The integration can be accomplished by an operator amplifier and a capacitor in a feedback circuit.