5. The logical gate not

The simplest components of digital electronics are the logical gates, which carry out basic logical operations. Combining these logical gates, much more complex circuits can be built, until you reach modern computers.

The simplest logical gate is the negation gate, also called Inverter gate or gate Not. This gate invests the value of the input signal, so that if the input is worth a logical one, the output will be worth a logical and vice versa.

The Gate symbol Not is as follows:

Puerta lógica NOT.

Logical Gate Not.

The circle at the exit of the triangle is the one that represents that the gate invests, or denies, the entrance value.

The logical function of the not gate is represented by a line on the element to be invest or deny:

Out = \overline{ A }

Below we can see the Truth Table of the Not Puerta, which represents all possible values ​​of entry and exit of the logical gate:

Tabla de verdad de puerta lógica NOT.

Truth Table of the logic gate not.

When the entry is worth zero, the output (out) will be worth one.

When the entrance is worth one, the output (out) will be worth zero.

Simulation

In the following simulation we can see a Not Puerta with an entry that can change value and an exit that is always worth the opposite of the entrance value.

In the simulator the values ​​can be represented with numbers (0, 1), with logical levels (L, H) or with voltage values ​​(0V, 5V), with the following correspondence:

Level Logical value Voltage value
L = low 0 = logical zero 0 volts
H = high 1 = logical one 5 volts

You have to click on the logical input value to change value.

Exercises

  1. What is a logical gate?

    What can be built with logical gates?

  2. Explain with your words the functioning of the logic gate not.

  3. Draw the Not gate symbol and write under its logical function and its three different names.

  4. Draw the Truth Table of the Not Puerta with numerical values​​ 0 and 1.

    Draw the Truth Table of the Not Puerta with logical levels L and H.

  5. Make a two -gate simulation in series. How do you think it will be the Truth Table of the two gates?

    Perform the simulation and draw the truth table of the two gates in series.