Digital Electronics

Difference between Analog and Digital. Digital refers to a discrete quantity. Analog refers to the quantities that vary with time on an ongoing basis.

A Logic circuit uses two logic levels to transfer the information. A high logic level or “1” and a low logic level or “0”. The Logic circuits are made of digital elements such as the AND gate, the OR gate, the NOT gate and a combinations of them.

In digital circuits, it is common to say that we have a “high or a “low” logic level at the input or output of a circuit. If we have a “high” level we say it is a “1” and if we have a “low” level we say that it is a “0”.

Truth Table is used to simplify boolean equations obtained from digital circuits. The truth tables can have many columns, but all tables operate in the same way.

Boolean Algebra is a tool to reduce logical expressions. It is the mathematics of logical expressions, which was presented by George Boole in 1854.

The Karnaugh map (K-map) is a widely used tool for simplifying logic circuits. When you have a logical function with its truth table, and you want to implement this function in the simplest and most economical way, this method is used.

The Binary Number System, unlike the Decimal Number System, where 10 figures are allowed (from 0 to 9), only needs 2 figures: “0” and “1”.

The hexadecimal numbering system (base-16). This numbering system is mainly used to simplify the representation of binary numbers and for the digital handling of colors.

In order to share information in digital format, it is common to use a binary or hexadecimal representations (BCD Code). There are other methods to represent this information and one of them is the BCD code.

The Gray code is a special type of binary code that is unweighted (the digits that make up the code does not have an assigned weight).

Aiken BCD code is similar to the natural BCD code, but with “weights” or “values” distributed differently. The Excess 3 Code is obtained by adding “3” to each combination of the natural BCD code.

The logic AND gate is one of the simplest gates in Digital Electronics. The output of an AND gate is true (“1”) only when all inputs are true (“1”). If one or more inputs are false (“0”), then the output is false (“0”).

The NAND gate, also called a universal gate, is a gate that produces a logic “0” output only when all logic inputs are “1”. The NAND gate truth table

The logic Or gate is one of the simplest digital logic gates. The output of this gate is “High”, when one or all of its inputs are “High”. We can also say that, the output of an OR gate is “Low” only when all gate inputs are “Low”.

The NOR Logic gate – Truth Table, equivalent circuit. It can be implemented with the concatenation of an OR gate and a NOT gate.

The NOT gate is a logic gate that has only one input and one output. The output logic level is the opposite of the input logic level

In digital electronics there are special gates. One of them is the XOR logic gate or exclusive OR gate. Equivalent XOR Logic Gate using common logic gates

This circuit simulates the operation of a NAND gate with two or more inputs. (There is one diode for each input. D1, D2, …)

Diode Logic OR gate (wired OR connection) and Diode Logic AND gate (wired AND connection). Diode Logic uses the fact that diodes conduct only in one direction. (they behave like switches)

A combinational circuit is a circuit where the output depends only on the combination of the inputs at the time we are testing the output

A sequential circuit is a circuit where there are one or more feed backs from one or more outputs. The new output depend on the inputs and the last output

The JK Flip-Flop is a sequential device with 3 inputs (J, K, CLK (clock signal)) and 2 outputs (Q and Q’). J and K are control inputs.