1 Isolator Construction

Even though both capacitive digital isolators and optocouplers offer similar functionality, these devices are quite different in construction and working principle. Optocouplers use an LED to transmit digital or analog information across an isolation (or insulation) barrier (often just an air gap). Some optocouplers use epoxy as the insulating material which offers slightly better dielectric strength than air, as shown in Figure 1-1. Conversely, capacitive digital isolators are constructed with two series isolation capacitors using SiO₂ as the dielectric, as shown in Figure 1-2. SiO₂ offers one of the highest dielectric strengths among insulating materials and is significantly stronger compared to dielectrics used by competing isolation technologies, as shown in Table 1-1.