4. Logic Gates

What are logic gates?

Are fundamental electronic circuits in digital systems, which perform logical operations/ boolean functions on one or more logical inputs and produce a single output.

What a logical inputs?

They are binary inputs - 0s (logic LOW) and 1s (logic HIGH)

Which represent TRUE/ FALSE or ON/ OFF

What are ideal logic gates?

Gates that perform logical operations/ boolean functions with,

• Zero rise time

• Unlimited fan loading

• infinite speed, zero power, zero delay and unlimited output driving ability

What categories can logic gates be divided into?

1. Basic Gates

2. Universal Gates

3. Advanced Gates

What are the Basic Gates?

AND, OR, NOT

What is the AND function?

It performs a logical multiplication.

• Output is HIGH, when both Inputs are HIGH

• Output is LOW, when any one of the Inputs is LOW

Find the answer for X

Applications of the AND gate

used to trigger actions if all the conditions are met

1. Building adders/ multipliers in CPUs (ALUs)

2. Controlling traffic lights

3. Security systems (multiple triggered)

4. Creating multiplexers/ decorders

What is the OR function?

Performs a logical addition.

• Output is HIGH, when any one of the Input is HIGH

• Output is LOW, when both Inputs are LOW

Find X

Applications of the OR gate

used to trigger actions if any of the conditions are met.

1. Alarm systems (Fire, car doors)

2. Control systems (detecting high temp, pressure)

3. Designing multiplexers

4. ALUs

5. Data routing

NOT gate function

Also known as the Inverter.

• Output is HIGH, when Input is LOW

• Output is LOW, when Input is HIGH

Universal Gates

What is a Universal gate?

A gate that can implement any BOOLEAN function without the need to use any other gate type.

Main two types of UNIVERSAL GATES?

NAND and NOR

Why is the practice of using Universal gates considered advantageous?

NAND and NOR gates are,

• Economical

• Easier to fabricate

• Are basic gates used in ICs

How are AND and OR gates typically implemented?

• AND gate = NAND gate followed by an inverter

• OR gate = NOR gate followed by an inverter

What is a NAND gate?

It is a contraction AND-NOT.

NAND gate function

• Output is HIGH, when both inputs are LOW/ any one of the input is LOW

• Output is LOW, when both inputs are HIGH

?

What does the bubble next to a logic gate indicate?

Active LOW state

What are ‘ACTIVE LOW’ and ‘ACTIVE HIGH’?

• ACTIVE LOW - Output is HIGH, when Input is LOW (inversely proportional)

• ACTIVE HIGH - Output is HIGH, when Input is HIGH (directly proportional)

What is a NOR gate?

It is a contraction of OR-NOT.

NOR gate function?

• Output is HIGH, when both inputs are LOW

• Output is LOW, when one or both inputs are HIGH

?

Applications of NAND and NOR gates

• Memory (latches, flip flops)

• Used as Universal gates

• Alarm systems, timers, encorders, decorders

• Creating CPUs

• Calculators

Find X?

Find X?

What is an X-OR gate? (Exclusive-OR) function?

It is digital logic gate where,

• Output is HIGH, when Inputs are different

• Output is LOW, when Inputs are the same

What is an Exclusive-NOR gate? (X-NOR) function?

It is a digital logic gate where,

• Output is HIGH, when Inputs are the same

• Output is LOW, when inputs are different

What is an integrated circuit (IC)?

also known as a chip or microchip, is a compact assembly of electronic circuits formed by various components such as transistors, resistors and capacitors, all fabricated on a single piece of semiconductor material, typically silicon.