A technical performance-based view of opto-isolators and digital isolators | EDN

Galvanic isolators are devices that couple an electrical data or control signal across an insulation barrier without any flow of current through it, thereby enabling signals to be transferred while blocking noise. The insulation barrier also safeguards equipment and human operators from high voltages.
The earliest isolators were optically coupled devices, also called opto-isolators or optocouplers, “optos” for short.
Optos were basically the only solution available until CMOS-based digital isolators were developed in the late 1990s using inductive (magnetic) or capacitive coupling to transfer the signal.
A prominent characteristic of the opto is the aging problem.
Digital isolators have no such physical limitations. In general though, digital isolators are superior in terms of timing characteristics, stability over lifetime, CMTI, and high temperature operation.


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