Optocouplers are the usual choice for coupling digital signals between isolated circuits with different ground levels. Optocouplers have disadvantages, however. Their most important parameters, current transfer and propagation time, change with aging. They have a relatively high static power consumption and, for most types, limited speed. In this application note, an unorthodox application of a pair of MOSFET-driver ICs and a ferrite-bead transformer yields a single-channel, isolated digital-signal coupler.