Electronic Coupling and Circuit Isolation Using an Electro-Optical Device

摘要

A load-sensitive LC oscillator was designed and constructed to demonstrate the effectiveness of a photoncoupled-pair (PCP), operating as a photon-coupled isolation amplifier (PCIA), in coupling a signal from the tank of the oscillator. Loading effects on the output of the oscillator are compared for both PCIA and capacitive methods of coupling. Results show that the PCIA provides complete isolation between load and oscillator for load resistance as low as 10K ohms. A new PCP showed promise of even greater isolation ability. In contrast, loading through capacitive coupling disabled the oscillator at a load value of 560K ohms. The use of the PCIA to isolate the load resulted in improvement of the oscillator frequency stability from a deviation of one part in 500 to one part in 100,000. Frequency response, distortion, and input-output characteristic curves are presented, along with an equivalent circuit, to: (1) assist in characterizing a typical PCP, and (2) provide tools necessary to explain the operation, limiting features, and isolation advantages of a PCP when it is used as an electronic signal coupler. (Author)