Design of CMOS NAND gate

Summary

In this video, Dr. Shan Nikam from AISSMS Institute of Information Technology explains the design of a NAND gate using CMOS technology. He covers the fundamentals of logic gates, distinguishing between basic gates and universal gates like NAND and NOR. The presentation details the operation of N-channel and P-channel MOSFETs, illustrating their roles in the pull-up and pull-down networks. Key design rules and the truth table are also discussed to demonstrate the functionality of the NAND gate, emphasizing the significance of MOSFETs in digital circuits. Viewers are encouraged to engage with the content.

Takeaways

• 😀 Logic gates are the fundamental building blocks of digital systems, with NAND and NOR gates being universal gates capable of implementing any logic.
• 😀 The video focuses on designing a NAND gate using CMOS technology, specifically using MOSFETs.
• 😀 MOSFETs can be classified into N-channel, which turns on with high voltage, and P-channel, which turns on with low voltage.
• 😀 A CMOS NAND gate consists of a Pull-Up Network (PUN) using P-channel MOSFETs and a Pull-Down Network (PDN) using N-channel MOSFETs.
• 😀 In CMOS design, N-channel MOSFETs are used for low voltage (ground) and P-channel for high voltage (VDD).
• 😀 There are specific design rules to follow: use P-channel in PUN, N-channel in PDN, connect N-channel in series for multiplication, and in parallel for addition.
• 😀 The symbol for P-channel MOSFETs includes a bubble at the gate terminal, differentiating them from N-channel MOSFETs.
• 😀 The truth table for the NAND gate is crucial for verifying its operation under different input conditions.
• 😀 For the input conditions (A=0, B=0), the output Y is 1, indicating that the gate is functioning correctly as a NAND gate.
• 😀 The video concludes with an invitation to engage with the content by liking, sharing, and subscribing.

Q & A

What is the primary focus of this video?

The video focuses on the design of a NAND gate using CMOS technology.

What are the basic building blocks of digital systems?

The basic building blocks are logic gates, which include basic gates like AND, OR, and NOT, as well as universal gates like NAND and NOR.

Why are NAND and NOR gates considered universal gates?

NAND and NOR gates are considered universal gates because any logic function can be implemented using only NAND or only NOR gates.

What two types of technology are primarily used to fabricate logic gates?

Logic gates are primarily fabricated using TTL (Transistor-Transistor Logic) and CMOS (Complementary Metal-Oxide-Semiconductor) technologies.

What are the two types of MOSFETs used in CMOS technology?

The two types of MOSFETs are N-channel MOSFETs, which turn ON with a high voltage, and P-channel MOSFETs, which turn ON with a low voltage.

What role do P-channel MOSFETs play in a NAND gate design?

P-channel MOSFETs are part of the pull-up network in a NAND gate design, pulling the output to VDD (the supply voltage).

What happens when both inputs of a NAND gate are 0?

When both inputs are 0, the P-channel MOSFETs turn ON, pulling the output up to VDD, resulting in an output of 1.

How are N-channel MOSFETs connected for multiplication in a NAND gate?

For multiplication (AND operation), N-channel MOSFETs are connected in series.

What must be remembered when connecting N-channel MOSFETs in parallel?

When connecting N-channel MOSFETs in parallel, they must also be connected in series for proper function.

What is the output when both inputs of a NAND gate are 1?

When both inputs are 1, both P-channel MOSFETs turn OFF, and both N-channel MOSFETs turn ON, pulling the output down to ground, resulting in an output of 0.

Outlines

00:00

🔌 Design of NAND Gate Using CMOS Technology

This video focuses on the design of a NAND gate using CMOS (Complementary Metal-Oxide-Semiconductor) technology. It begins with an introduction to logic gates, categorizing them into basic gates (AND, OR, NOT), universal gates (NAND, NOR), and derived gates (XOR, XNOR). The universal NAND gate is the focus, as it can implement any logic function when used alone. The video explains how gates can be implemented using two technologies: TTL (Transistor-Transistor Logic) and CMOS, with an emphasis on the latter. CMOS technology uses two types of MOSFETs (N-channel and P-channel) that work in complementary fashion. The video discusses the roles of these MOSFETs, the pull-up and pull-down networks, and the rules for designing CMOS logic gates, including the series and parallel connections required for multiplication and addition operations. A diagram illustrates the implementation of a 2-input NAND gate, explaining how the P-channel MOSFETs are used in the pull-up network and the N-channel MOSFETs in the pull-down network. The truth table of a NAND gate is also verified, detailing the behavior of the MOSFETs under various input conditions and explaining how the output is determined.

Keywords

💡NAND Gate

The NAND gate is a fundamental digital logic gate that produces an output which is false only when all its inputs are true. It is considered a universal gate because any other gate can be implemented using only NAND gates. In the video, Dr. Shan discusses the implementation of a NAND gate using CMOS technology, emphasizing its importance in digital systems.

💡CMOS Technology

Complementary Metal-Oxide-Semiconductor (CMOS) technology is a widely used semiconductor technology for constructing integrated circuits, including microprocessors, batteries, and image sensors. The video highlights how CMOS technology employs both N-channel and P-channel MOSFETs to create efficient digital logic gates. Its significance lies in its ability to consume less power compared to other technologies, making it ideal for modern electronic devices.

💡MOSFET

MOSFET, or Metal-Oxide-Semiconductor Field-Effect Transistor, is a type of transistor used for switching and amplifying electronic signals. In the context of the video, MOSFETs act as switches in the design of the NAND gate. The video explains the behavior of N-channel and P-channel MOSFETs, noting that N-channel MOSFETs turn on with high voltage, while P-channel ones activate with low voltage.

💡Pull-Up Network

The Pull-Up Network in a CMOS circuit is responsible for connecting the output to a high voltage level (VDD) when needed. In the video, Dr. Shan explains that P-channel MOSFETs are used in the Pull-Up Network to pull the output high, demonstrating how these components work together in a NAND gate design. This network is crucial for ensuring the output reflects the correct logical state.

💡Pull-Down Network

The Pull-Down Network is the counterpart to the Pull-Up Network, connecting the output to ground (low voltage) in a CMOS circuit. The video emphasizes the role of N-channel MOSFETs in the Pull-Down Network, which pull the output low when activated. Understanding this network is essential for designing effective digital circuits, as it influences the output states of the logic gate.

💡Logic Gates

Logic gates are the building blocks of digital circuits, performing basic logical functions on one or more binary inputs to produce a single output. In the video, Dr. Shan discusses various types of logic gates, including AND, OR, and NOT gates, as well as their significance in digital systems. Understanding how these gates operate is fundamental to grasping how complex digital circuits are constructed.

💡Universal Gates

Universal gates are types of logic gates that can be used to create any other type of logic gate. The video focuses on NAND and NOR gates as universal gates because they can be combined to form any logical function. This versatility makes them integral to digital circuit design, as they simplify the implementation of complex logic.

💡Truth Table

A truth table is a mathematical table used in logic—specifically in connection with Boolean algebra, digital logic, and computer science. The video uses a truth table to demonstrate the output of the NAND gate based on different combinations of its inputs (0s and 1s). This tool is essential for understanding how the gate behaves under various conditions and verifying its logic.

💡Boolean Function

A Boolean function is a function that delivers a result based on logical inputs that can be either true or false (1 or 0). In the video, Dr. Shan explains that any Boolean function can be realized using the combination of the Pull-Up and Pull-Down Networks. This concept is critical for understanding how to implement logical operations in digital circuits.

💡Series and Parallel Connections

In the context of circuit design, series and parallel connections refer to the ways in which components (like MOSFETs) are arranged in a circuit. The video explains that N-channel MOSFETs are connected in series for multiplication and in parallel for addition. Understanding these configurations is vital for effectively designing digital logic circuits, as they directly impact the circuit's functionality.

Highlights

Introduction to the NAND gate design using CMOS technology.

Basic building blocks of digital systems are logic gates.

Universal gates include NAND and NOR gates, capable of implementing any logic function.

Difference between basic gates and derived gates like XOR.

MOSFETs (N-channel and P-channel) act as switches in digital circuits.

N-channel MOSFETs turn on with high voltage, while P-channel MOSFETs turn on with low voltage.

Complementary MOS (CMOS) technology combines N-channel and P-channel MOSFETs.

Pull-up and pull-down networks are essential for CMOS NAND gate implementation.

Rules for connecting MOSFETs: N-channel in series for multiplication and in parallel for addition.

Truth table verification of the NAND gate's operation.

NAND gate outputs 1 when both inputs are 0, illustrating the function of MOSFETs as switches.

Output behavior when one input is high: only one P-channel MOSFET turns off, keeping the output high.

Output goes low (0) when both inputs are high due to direct grounding through N-channel MOSFETs.

The CMOS NAND gate's implementation and operation can be verified by treating MOSFETs as switches.

Emphasis on the importance of understanding digital systems through MOSFET configurations.

Conclusion encouraging viewers to like, share, and subscribe for more educational content.

Transcripts

hello everybody Welcome to my channel

circuitry simplified by Dr Shan nikam

I'm working with aissms Institute of

information Technologies department of

entc engineering this video is all about

design of nand gate using seos

technology so basic building block of

any digital system is a gate and Gates

can be either basic Gates which are and

gate or gate and not gate or inverter

Universal gates are nand gate and

Norgate they are Universal Gates because

we can Implement any logic using only

nand Gates or only n Gates then there

comes derived Gates which are exor gate

and exor gate here in this video we'll

talk about implementation of one

universal gate and that is nand gate so

the logic gates are the basic building

blocks and these logic gates can be

implemented using either TTL technology

where we use BJT bipolar Junction

transistor for fabrication and in case

of camos technology we use mosfets and

here in this video we'll talk about

implementation of nandate using mosfet

technology we will not talk about

bjts so when we implement our gate using

MOS Fates mosfit act as a switch so it

acts as either on or off switch so there

are two types of mosites n Channel

mosfit and P channel mosfets

so uh the N MOS turns on when the

voltage is high and it turns off when

the applied voltage is low whereas in

case of P Channel mosfit it turns on

when we apply low voltage and it turns

off when we apply high voltage here in

digital when we say low it means zero

and when we say high it is one so zero

is always ground or 0 volts whereas one

can be 5 volt it can be 3.3 volt for

some technology node it can be 1.2 for

some technology node it can be 1.8 for

some technology node technology node

means the transistor size 180 nanom or

90 nanom or 22 nanom but when we use

both n Channel mosfit as well as P

channel mosfit for implementation of

digital systems it is called as c moss

complimentary moss and the reason they

are called complimentary is that n moss

and P Moss work in complimentary

fashion so so implementation of seos

logic gate we use pullup Network which

pulls output to vdd and we also use pull

down Network which pulls output to D

down or ground so we use P channel

mosfets in pullup Network and N channel

mosfets in pull down Network so any

Boolean function can be realized using

pullup Network and pull down Network

so when we design circuitry using p in

pullup and nmos in pull down there are

certain rules which we need to follow so

see in digital systems how do we design

them we can either design them as sum of

product or product of sum it means we

need to perform two operations

continuously and these two operations

are

addition and multiplication so here rule

number one is use P channel mosfets in

pull up Network second rule is use n

channel mosfets in pull down Network

third and very important rule is to

implement

multiplication n channel mosfets are

connected in

series whereas to implement addition it

means if equation is y equal to a + b

then there is an addition then n channel

mosfets are connected in parallel so for

multiplication n Mo are in series for

addition n Mo are in parallel and last

and the most important rule is when n Mo

are connected in parallel then we must

must be connected in series and vice

versa so see here implementation of seos

n look at this diagram here you can see

this is n Channel mosfet the other one

is also n Channel mosfit and this

network is called as pul down Network

the upper part is called as pullup

Network here you can see the difference

in the symbol of P MOS and N mos in the

symbol of P MOS it has Bubble at gate

terminal so here our SOS nand is two

input SOS nand it has two input so we

will take two n Channel MOS Fates and

two P Channel MOS Fates in case of

implementation of three input Nate we'll

take three n Channel MOS Fates and three

p Channel MOS Fates so n is nothing but

inverted and and what we Implement using

n multiplication operation so we'll

connect n moss in series is and P Mo in

parall so let's verify truth table of

our nand gate so very first condition is

a is equal to 0 and B is equal to 0 so

here mosfet acts as what switch so it is

either closed switch or open switch so

for z0 condition when a is equals to z

and b is equals to 0 BOS turns on when

inputs are zero so here both pmos will

turn

on they'll act as closed switches and

both end channel mosfets will remain

off as P channel mosfets are on N

channel mosfets are off so current will

flow from vdd to Output Y and it will

charge the output capacitance or in

simple words you can say y will get

pulled up to V DD so when both inputs

are 0 0 Y is equal to 1 then let's uh

see case number two and case number two

when either of two inputs is zero so a

is equal to 0 and B is equal to 1 or a

is equals to 1 and B is equals

to0 so in these two conditions out of

two P channel mosfets one is on and

other one is off and out of two n

channel mosfets the one which receives

one is on and the other one is

off so here there is no direct path

between Y and ground either of two

mosfets one is continuously off so it's

it acts as a open switch so current

cannot flow through this path because of

open switch whereas here in P up Network

even if one mosfet is off another mosfet

is on so current it acts as closed

switch so current can flow from vdd

through that closed switch to Output Y

and output y will get pulled up to vdd

so for case number two and case number

three outputs are 1 now the last case

when a is equal to 1 and B is equal to 1

so here both P channel mosfets will

remain off they'll act as open switch

and both n channel mosfets will turn on

and they'll act as closed switch so here

you can see there is a direct path for

current to flow from y to ground but

there is no path for current from vdd to

Output y so output y will get pulled

down to ground so y will get connected

to ground directly so output is equals

to

zero so in this way our seos nand gate

can be

implemented and you can verify its

operation also by considering mosfet as

a

switch thank you so much for watching

don't forget to like share and subscribe

see you in next video thank you