Figure 2-3 shows the typical block diagram and the equivalent circuit of the active single-switch architecture. In the figure, the IMD circuit is connected to neutral, while the circuit can also be placed in line or chassis. This architecture is characterized by having one switch and one external bias supply.

The basic working principle is based on the equivalent circuit when SN closes. The DC bias supply is the voltage source of the circuit. The effective insulation resistance of the system can be solved according to the resistor divider.