5 Signal Isolation

A key performance metric of any switch is how well it isolates signals across the switch when off. See the equivalent circuit diagram shown here Figure 5-1. Ideally, the switch's off-resistance will be very high and the capacitance from input to output will be very low. When a signal is present on one side of the switch, we can calculate the ratio of output voltage to input voltage in dB across a frequency range. For Photorelay and multiplexer devices, Off-isolation performance is comparable across frequency but can vary depending on architecture. TI’s Flat On-Resistance Multiplexers have a slight advantage due to an internal isolation shunt.