Isolation amplifier having improved fidelity

Abstract

An isolation amplifier comprising three separate conductively-isolated sections: (1) an input section including an AC modulator, (2) an output section including a demodulator, and (3) an improved oscillator or AC power section for reducing the undesirable effects of common mode interference signal sources coupled thereto through stray capacitance. The improved oscillator or power portion includes control elements for controlling the timing and direction of current conduction through the primary winding of a transformer having its secondary connected to the chopper or modulator. The control elements and circuitry associated therewith conduct in alternation and in a manner resulting substantially in conduction-overlap. Such conduction overlap is accomplished by means which accelerate initiation of conduction in one control element and possibly also retard the cessation of conduction in the other control element. In one embodiment, the conduction controlling circuitry of the AC power section includes two pairs of oppositely-conductive types of semi-conductors having their collector-emitter circuits connected in series with the transformer primary and across a DC power buss. Conduction-control of the respective semi-conductors is effected by a square wave control signal applied to the respective base elements thereof through respective speed-up capacitors.