Practical Electronics/Logic/Transmission Gates

Transmission gates represent a very useful application of logic gates. A transmission gate allows a signal to pass only when a certain condition is met, and the same gate can also invert the signal if necessary.

AND Transmission Gate

This is the basic transmission gate. The "condition signal" is one input, and the "signal input" is the other. When the condition input is high, any high at the signal input will result in a high at the output, and a low at the signal input will result in a low. Therefore, the signal at the signal input is "transmitted" through the gate when the condition signal goes high.

Summary

The table below summarises the type of transmission gates you need to use to produce the right behaviour:

	Non-Inverting	Inverting
Normally High	OR	NAND
Normally Low	AND	NOR