Introduction to Logic Gates

Non-Inverter or Buffer

At a non-inverter, also known as buffer, the value entered on its input will be found on its output. You may think that this is a crazy logic gate, since it does nothing. That’s not true, it has several important applications on digital electronics, as we will explain below.

Figure 23: Non-inverter or buffer.

A typical application for a buffer is to increase the fan-out of a given logic gate. Fan-out is the maximum number of gates a given integrated circuit is capable of being connected to. For example, if a given logic gate has a fan-out of 3 gates, its output can be only connected directly to three other logic gates. If you need to connect its output to more logic gates, you can use a buffer to increase the number of logic gates you can connect this output to.

Another application for the buffer is the use of a circuit where the buffer is controlled by a gate (74367 integrated circuit is a good example). In this application this logic gate will work like a gate: it will only replicate what is on its input when its gate pin is activated.

Figure 24: 74367 integrated circuit pinout.

One more application for a Non-Inverter is to create a delay line. Since each integrated circuit delays a little bit to replicate what is on its input on its output, a non-inverter can be used to delay the signal. This idea is used on some digital oscillator circuits, for example. If you take the circuit in Figure 25, if each gate delays the signal 10 ns (nanoseconds), with four gates we will have a 40 ns delay line.

Figure 25: A delay line.

Another very common application for both non-inverters and inverters is to drive circuits that need more current or need to work with voltages different from 5 V as “1”. This topic is really important and we will be explaining that in the next page.