# Transmission Gates Transistors can be used to transmit signals from the source to drain. We can combine PMOS and NMOS [Pass transistors](Pass%20transistors.md) to obtain the best of both worlds:  ## Symbol  ## Common Uses ### Transmission Gate Multiplexer Can embed the logic function into the structure. A 4 way multiplexer needs 8 transmission gates.  This multiplexer makes no assumption about what the input signals are! - They could be analogue or digital. - There is also no signal direction flow (A-Y or Y-A equally valid) Can be a multiplexer or a demultiplexer - for demux, might want to think about some sort of pull down for open circuited signals.  ## Compact Logic Functions  If B is Low, the output will be A_bar, if B is high, output is A. This implements XNOR: $Y=\overline{A\oplus B}$ Swapping B and B_Bar gives XOR: $Y={A\oplus B}$  This is the most compact way to implement XOR and XNOR. ### Drawbacks - Propagation Delay through the gate depends on what signal drives the A input (not desirable) - Need Complement of the A input [^1] --- # References [^1]: [vr-4602-wk09-sc03-transmissiongates](../../Spaces/University/ELEC4602%20–%20Microelectronics%20Design%20and%20Technology/Lectures/W9/vr-4602-wk09-sc03-transmissiongates.mp4)