4093 Quad 2-Input NAND Schmitt Trigger

The 4093 is a CMOS chip with four NAND gates with a Schmitt trigger. Because each gate has two inputs and has four gates inside, it’s often referred to as a Quad 2-Input NAND Schmitt Trigger.

A NAND gate with a Schmitt trigger works more or less like a normal NAND gate. With the exception that the threshold for when it switches from LOW to HIGH is different from when it switches from HIGH to LOW.

Pin Overview

What is a NAND gate with Schmitt Trigger?

First of all, a NAND gate is a logic gate that works like an AND gate with a NOT gate on the output. Therefore it’s often called NOT-AND.

This means that a NAND gate gives a LOW output only when all inputs are HIGH as shown in the truth table below.

Schmitt Trigger

But this is a Schmitt trigger NAND gate. What does that mean?

This has to do with at what voltage the gate will interpret the input as a LOW or a HIGH input:

For example for a normal (non-Schmitt Trigger) gate that is powered from 5V, the gate might say that any voltage above 2.5V is HIGH, and any voltage below 2.5V is LOW. So if the input is at 2.5V and swinging a bit up and down (as these signals tend to do), then the output would be uncertain.

2.5V would be the threshold voltage.

But for a Schmitt trigger gate, the threshold voltage is different based on if the input changes from LOW to HIGH or from HIGH to LOW.

For example, if the input is currently LOW, then a Schmitt trigger gate might require the input voltage to go above for 3.5V to switch to HIGH. But when it has switched to HIGH, dropping a bit below 3.5V doesn’t matter. Because in order to switch back to LOW, the Schmitt trigger gate requires the input to go down below for example 1.5V.

Technical Specifications