Transmission Gates

• Write short notes on transmission gates (TG).

By connecting an nMOS and a pMOS transistor in parallel, we obtain a switch that turns on when a 1 is applied to the gate terminal in which 0’s and 1’s are both passed in an acceptable fashion.

We term this a transmission gate or pass gate.

transmission gate or pass gate

In a circuit where only a 0 or a 1 has to be passed, the appropriate transistor (n or p) can be deleted, reverting to a single nMOS or pMOS device.

Note that, both the control input and its complement are required by the transmission gate. This is called double rail logic.

When the control input is low( control =0), the switch is open, and when the control is high (control=1) the switch is closed.