M3: The Logic Gates

Logic Gate

• It is a basic electronic building block used in digital circuits.

• It performs a logical operation on one or more binary inputs (0 or 1) to produce a single binary output (0 or 1)

• They're physical devices that perform Boolean algebra, a branch of mathematics dealing with logical operations on binary variables.

• Low state, represents a 0 volts in its application

• High state, represents a 5 volts in TTL and 3.3 in some mid-generation CMOS

A logic gate works in the binary system, so it only has two states:

Logic families

• __________ are groups (families) of electronic logic gates that are built using the same type of electronic components and have similar electrical characteristics (like speed, power consumption, and voltage levels).

• In other words, it’s a technology used to build logic gates in digital circuits.

• Diode Logic (DL)

• Resistor–Transistor Logic (RTL)

• Diode Transistor Logic (DTL)

• Transistor–Transistor Logic (TTL)

• Emitter-Coupled Logic (ECL)

• CMOS (Complementary Metal-Oxide-Semiconductor)

• BiCMOS (Bipolar Complementary Metal-Oxide-Semiconductor)

Types of Logic Families:

Diode Logic (DL)

• oldest and simplest

• uses only diodes and resistors

• cannot provide amplification (weak signal)

• rarely used now

Resistor–Transistor Logic (RTL)

• uses resistors and bipolar transistors

• faster than diode logic

• higher power consumption

• mostly obsolete now

Diode Transistor Logic (DTL)

• uses diodes for logic and transistors for amplification

• improved over RTL

• used before TTL became common

Transistor–Transistor Logic (TTL)

• uses bipolar junction transistors (BJTs)

• very popular in older computers and digital circuits

• faster than DTL, moderate power

Emitter-Coupled Logic (ECL)

• uses BJTs in differential amplifier configuration

• very high speed

• high power consumption

• used in high-speed applications

CMOS (Complementary Metal-Oxide-Semiconductor)

• uses complementary MOSFET transistors (NMOS + PMOS)

• very low power consumption

• high noise immunity

• very widely used today (in microprocessors, memory chips, etc.)

BiCMOS (Bipolar Complementary Metal-Oxide-Semiconductor)

• Combines BJT (bipolar) and CMOS

• High speed like TTL + low power like CMOS

• Used in advanced, high-performance circuits

Memorize it!!

Integrated Circuit (IC)

• It is a tiny electronic circuit built on a small flat piece (chip) of semiconductor material, usually silicon, that can contain millions or even billions of microscopic components like: Transistors, Diodes, Resistors, Capacitors

• Complete electronic circuit built into a single small chip that makes modern electronic devices smaller, faster, cheaper, and more reliable.

Legacy Gates (Fundamental Gates)

• NOT Gate

• OR Gate

• AND Gate

• YES Gate (Buffer)

Universal Gates

• NOR Gate

• NAND Gate

Derived Gates

• XOR Gate (Exclusive OR Gate)

• XNOR Gate (Exclusive NOR Gate)

Types of Logic Gates:

NOT Gate

• also known as Inverter

• the output is the complement of the input

OR Gate

• follows the principle of addition

• any input of “high” will results to a “high output”

AND Gate

• follows the principle of multiplication

• any input of “low” will results to a “low output”

YES Gate (Buffer)

• also considered as a legacy gate

• the output follows whatever the input

NOR Gate

• an OR gate followed by an inverter

• Any input of “high” will results to a “low output”

NAND Gate

• an AND gate followed by an inverter

• any input of “low” will results to a “high output”

XOR Gate (Exclusive OR Gate)

• sometimes called Inequality detector, because it outputs 1 when the inputs are different (unequal)

• sometimes called Modulo-2 adder, because it performs binary addition without carry

XNOR Gate (Exclusive NOR Gate)

• Sometimes called Equivalence gate or Equality detector because it outputs 1 when the inputs are the same

Logic Gate Symbols of AND and OR:

Logic Gates Symbols of NOT, NAND, NOR, XOR, XNOR and BUFFET: