Intro to Digital Electronics

Classifications of Electronic Circuits

• Switching Circuits – by turning electricity on and off. – Figure 1– Known as the digital method.

• Regulating Circuits – controls intensity of current. – Figure 2– Known as the analog method

Figure 1 – Current is On or OffFigure 2 – Increase/Decrease Current

What’s Digital and AnalogDigital Analog

ComputersMicroprocessorsWatchesDisplays

Audio AmplifiersRadiosTelevisions – stations have recently gone digital

Why Digital?

• Digital electronics are simple, practical, and reliable.

• Combines simple switches and gates to create electrical functions.

• Digital means switching.– HI or 1 (one) or On– LO or 0 (zero) or Off

Truth Table of a Digital Circuit

• The operation of the circuit to the right is represented by the table.

• Describes switch and output status.

• Truth tables represent the operation of a circuit.

Truth Table

Switch Bulb

OPEN OFF (LO or 0)

CLOSED ON (HI or 1)

Timing Diagrams of a Digital Circuit

• Timing diagrams may also represent a digital circuit operation, in this case resistor voltage.

Logic Gates

Logic?

• Logic circuits are circuits that make decisions based on the inputs they receive.– Remember what the

digital signals can be?– 1 or 0; HI or LO; On or

Off

Logic Indicators

• Logic Indicator is a device that indicates the logic state (either HI or LO) of a certain point in a circuit.– Usually a LED

Boolean Algebra

• Conventional Algebra has 4 basic operations– Addition, subtraction, multiplication, division

• Boolean Algebra has 6 basic operations– AND, OR, NAND, NOR, NOT, YES

• Example: Using the AND Gate– Read as “A anded B equals Q”– Also read as A B = Q

• Try using the OR Gate:

QB

A

QB

A

The AND Logic Gate

A B Q1 1 11 0 00 1 00 0 0

When is the output of this

gate HI?

Boolean EquationA B = Q

The OR Logic Gate

A B Q1 1 11 0 10 1 10 0 0

When is the output of this

gate HI?

Boolean EquationA + B = Q

The NOT (Inverter) Logic Circuit

A Q1 00 1

The NOT logic circuit is also called

the “inverter”.

Boolean EquationA = Q

“A is equal to not Q”

Widely used in many circuits; NAND and NOR gates are created by adding inverters to AND and OR gates.

The YES Logic Circuit

A Q1 10 0

The input is the same as the output.

Also used as:Amplifiers – makes a weak

signal strong. Buffers – Isolates delicate

circuits

Boolean EquationA = Q

“A equals Q”

Transistors

3904 3906

The NOR Logic Gate

A B Q1 1 01 0 00 1 00 0 1

The result of this Gate is always

the opposite of an OR Gate.

Boolean EquationA + B = Q

The OR Gate vs. the NOR Gate

The OR Gate The NOR Gate

A B Q1 1 11 0 10 1 10 0 0

A B Q1 1 01 0 00 1 00 0 1

The NAND Logic Gate

A B Q1 1 01 0 10 1 10 0 1

The result of this Gate is always

the opposite of an AND Gate.

Boolean EquationA B = Q

The AND Gate vs. the NAND Gate

The AND Gate The NAND Gate

A B Q1 1 11 0 00 1 00 0 0

A B Q1 1 01 0 10 1 10 0 0