A transmission gate, or analog switch, is defined as an electronic element that will selectively block or pass a signal level from the input to the output. This solid-state switch is comprised of a pMOS transistor and nMOS transistor. The control gates are biased in a complementary manner so that both transistors are either on or off.
When the voltage on node A is a Logic 1, the complementary Logic 0 is applied to node active-low A, allowing both transistors to conduct and pass the signal at IN to OUT. When the voltage on node active-low A is a Logic 0, the complementary Logic 1 is applied to node A, turning both transistors off and forcing a high-impedance condition on both the IN and OUT nodes. This high-impedance condition represents the third “state” (high, low, or high-Z) that the DS3690 channel may reflect downstream.