CMOS NAND Gate Explained: Circuit, Working, Implementation, and Truth Table
Summary
TLDRIn this VLSI lecture, Professor Redes Dolaqia explains the design of a CMOS NAND gate. The lecture covers the basic functionality of a NAND gate, its Boolean equation, and truth table. The professor then details how to implement the NAND gate using CMOS transistors, specifically N-type and P-type MOSFETs (nMOS and pMOS). The explanation includes the pull-up and pull-down networks, the series and parallel connections, and how the circuit operates under different input conditions. The video concludes with a functional analysis of the circuit and a request for viewer feedback.
Takeaways
- π₯οΈ The video introduces the design of a CMOS NAND gate, explaining the structure and function of the gate.
- π The NAND gate's Boolean equation is Y = (A β B)Μ , with two inputs, A and B, where the output Y is determined by the logic.
- π’ The truth table for the NAND gate shows that if any input is 0, the output will be 1. Only when both inputs are 1 will the output be 0.
- π The NAND gate is implemented using CMOS transistors, specifically pMOS and nMOS transistors.
- πΆ For the NAND gate, the pull-up network is made with pMOS transistors in parallel, and the pull-down network is made with nMOS transistors in series.
- βοΈ The basic structure of a CMOS circuit includes a VDD power supply at the top, a pull-up network (pMOS), a pull-down network (nMOS), and an output in between.
- π§ The operation of the NAND gate using CMOS transistors depends on the connection of pMOS and nMOS in the circuit, which changes based on the logic values of A and B.
- π When A and B are 0, both pMOS transistors are on and nMOS transistors are off, resulting in a logic 1 output.
- π§ The video discusses how pMOS transistors are on when the gate input is 0, and nMOS transistors are on when the gate input is 1.
- π² The circuit behavior changes with different combinations of A and B values, explaining how the NAND gate functions through pMOS and nMOS transistor activity.
Q & A
What is the Boolean equation of a NAND gate with two inputs?
-The Boolean equation of a two-input NAND gate is Y = (A Β· B)'. This means the output Y is the complement of the AND operation between inputs A and B.
What happens to the output of a NAND gate when any of the inputs is 0?
-If any of the inputs to a NAND gate is 0, the output will always be 1.
How many possible input combinations exist for a two-input NAND gate?
-For a two-input NAND gate, there are four possible input combinations: (0,0), (0,1), (1,0), and (1,1).
What is the output of a NAND gate when both inputs are 1?
-When both inputs of a NAND gate are 1, the output will be 0.
How are PMOS and NMOS transistors arranged in a CMOS NAND gate?
-In a CMOS NAND gate, PMOS transistors are arranged in parallel, while NMOS transistors are arranged in series.
What is the role of the pull-up and pull-down networks in a CMOS NAND gate?
-The pull-up network, made of PMOS transistors, is responsible for providing a connection to the positive supply (VDD) when activated, while the pull-down network, made of NMOS transistors, connects the output to ground when activated.
What does it mean for a PMOS transistor to be 'on'?
-A PMOS transistor is considered 'on' when its gate input is at logic 0, causing it to behave like a short circuit.
What is the function of an NMOS transistor when its gate is at logic 1?
-When the gate of an NMOS transistor is at logic 1, the NMOS is 'on' and acts as a short circuit, allowing current to flow.
What is the output of the CMOS NAND gate when both inputs A and B are 0?
-When both inputs A and B are 0, the output will be logic 1, as both PMOS transistors (Q1 and Q2) will be on, and both NMOS transistors (Q3 and Q4) will be off.
How does the CMOS NAND gate function when one input is 0 and the other is 1?
-When one input is 0 and the other is 1, the output will be logic 1 because at least one PMOS transistor will be on and one NMOS transistor will be off, preventing the output from being pulled to ground.
Outlines
π Introduction to CMOS NAND Gate Design
Professor Redes Dolaqia introduces the lecture by explaining the concept and function of a CMOS NAND gate. The professor first defines the NAND gate and its Boolean equation, Y = (A Β· B)', and illustrates its logic symbol. The professor then explains the truth table, detailing how the NAND gate produces an output of 1 when any input is 0, and describes the four possible input combinations. The paragraph concludes with an overview of how CMOS transistors (nMOS and pMOS) are arranged in series and parallel configurations to implement the NAND gate.
βοΈ CMOS Transistor Configuration for NAND Gate
The professor details how to configure pMOS and nMOS transistors in CMOS technology for a NAND gate. The pull-up network uses pMOS transistors arranged in parallel, while the pull-down network consists of nMOS transistors in series. The paragraph explains the connection process for each transistor based on the Boolean operation A Β· B, emphasizing the structural setup where pMOS transistors receive inputs in parallel and nMOS transistors are connected in series. The description also covers grounding and output extraction in the circuit, ensuring the proper formation of the NAND gate using CMOS technology.
π Functionality of CMOS NAND Gate
The professor walks through the CMOS NAND gate circuitβs functionality using a truth table and transistor states (q1, q2 for pMOS and q3, q4 for nMOS). The paragraph explains the behavior of pMOS and nMOS transistors in various input combinations (0, 0; 0, 1; 1, 0; and 1, 1). The explanation covers how the circuit yields different outputs based on the input values, detailing how pMOS transistors turn on with a logic 0 input and nMOS transistors activate with a logic 1 input. The paragraph illustrates each scenario step by step, concluding with the output results for each case. Finally, the professor invites viewers to provide feedback for future content.
Mindmap
Keywords
π‘CMOS
π‘NAND Gate
π‘Boolean Equation
π‘Truth Table
π‘PMOS Transistor
π‘NMOS Transistor
π‘Pull-Up Network
π‘Pull-Down Network
π‘Short Circuit
π‘Open Circuit
Highlights
Introduction to VLSI lecture series and CMOS NAND gate design by Professor Redes Dolaqia.
Explanation of the NAND gate's Boolean equation: Y = (A . B)' and its logic symbol.
Introduction to the NAND gate truth table with two inputs (A and B) and four combinations (00, 01, 10, 11).
Explanation of the NAND gate functionality: If any input is 0, the output is 1.
Detailing the implementation of a NAND gate using CMOS transistors: nMOS and pMOS.
In NAND gate design, pMOS should be connected in parallel and nMOS in series for dot operations.
Description of the pull-up network made with pMOS transistors and the pull-down network made with nMOS transistors.
Common CMOS structure: Pull-up network with VDD, pull-down network with ground, and the output taken in between.
Designing a CMOS NAND gate circuit by connecting pMOS in parallel and nMOS in series.
Explanation of the operation of nMOS and pMOS transistors: nMOS turns on with logic 1 and pMOS with logic 0.
Simulation of the circuit's functionality for different input combinations: 00, 01, 10, and 11.
For input 00: pMOS transistors are on, nMOS transistors are off, and output is logic 1 (VDD).
For input 01: pMOS Q1 is on, Q2 is off, nMOS Q3 is off, Q4 is on, and the output is logic 1.
For input 10: pMOS Q1 is off, Q2 is on, nMOS Q3 is on, Q4 is off, and the output is logic 1.
For input 11: pMOS transistors are off, nMOS transistors are on, and the output is logic 0 (ground).
Transcripts
welcome to vlsi lecture series i
professor redes dolaqia is going to
explain you design of
cmos nand gate in this video so here
first i'll explain you what is nand gate
how it functions
after that we will implement nand gate
by using
cmos transistor so in cmos transistor we
have nmos and pmos
so by using nmos and pmos we will
implement nand gate over here
so as if we talk about nand gate then
its boolean equation
that is y if my output is y
then y is equals to if i have two inputs
a
and b then a dot b whole bar
that is my boolean equation and as if we
talk about
its symbol then
its logic symbol that is this
where with and we need to place bubble
over here so this is my output y
and here we have input a and b
there can be multiple input even but
here i have shown you
two input nand gates so we have two
inputs a and b
now let me explain you true table
so in its truth table we have two inputs
over here
a and b and my output
that is y so see
if you see the working of nand gate then
it explains
if any input is logic 0
then output is 1 so for nand gate if any
input is logic 0
then output will be 1 so with input a
and b
there are total 4 combinations 0 0
0 1 1 0 and 1 1
and if you see working if any input is 0
output is 1. so 0 0 1 here 0
1 means 0 input is there so output is 1
1 0 that is even 1 1 and 1 1 means 0
here there is no input which is 0 means
output is
1 so this is how true table is there
with
nand gate now before we implement
this nand gate by using cmos we should
know some basics
see here in nand operation
we have dot operation right
so when you perform dot operation you
see a dot b
whole bar so when you have dot operation
at a time
you should have pmos in parallel
and you should have nmos in series
so in dot operation pmos that should be
there in parallel
and nmos that should be there in series
now here one more thing that one should
know
see when you implement
any logic gate by using cmos transistor
its structure should be like this here
we should have vdd supply
and here i am just considering one block
and this block that is made up of
pull up network and pull up network
that we have it by having pmos
transistor
so here with pmos transistor we have
multiple inputs
right and after that there will be pull
down network so i am considering a block
so this is my pull
down network and pull down network that
should be made up of
nmos transistor and here i am showing
inputs to nmos transistor here we should
ground this
and output that will be coming from here
right so this is how common structure is
there
with cmos right where
after vdd there should be pull up
network and below that there will be
pull down network
and in between that there will be output
like this
right now let us try to understand how
to
implement this nand gate by using
pmos and nmos right so pull up network
that will be by pmos
and pull down network that will be by
nmos now you see
in nand gate as i have told you
it is a dot b whole bar so operation
is dot operation and in dot operation
pmos
should be there in parallel and nmos
should be there in series
right so you see here
we have vdd as per this
right after that there is pull up
network now we need to have
pmos transistor connection now see in
dot operation
pmos should be there in parallel so here
i am connecting
pmos in parallel right and
here we have operation that is a dot b
so
he here pmos is having input
a and it should be in parallel
and here we have second pmos that is
having input
b and you see
those two are in parallel over here so
this is my
pull up network now
see in pull down network there will be
nmos
and here in dot operation nmos should be
there in series
so here i am connecting nmos
in series you see
so with one nmos input is a
and with second and mos input is b and
this is what i need to ground
so this is my pull down network and here
i'll be taking output
right so this is how we can form a
circuit
of nand gate by using cmos
in cmos with upper network we will be
having pull up network and with this
we will be having pull down network
now let us try to understand how this
circuit functions
by truth table so it will be giving you
more clear idea
so here we have input
a and b and here we will be having
transistors
so here i have let us say this is q
one is q two this is q three
and this is q four so this is my q 1
q 2 and these are p mos
and here we have q 3 and q 4
and these are n
mos and here i have output
y so this is how i am going to make
a truth table and we will see how
this circuit functions right
now before i explain you how this
circuit functions
one should know how pmos and nmos
functions so let me explain you how pmos
and nmos functions
so here if i talk about nmos
then this is my nmos
where this is my gate terminal and if
you see this connection in that
here there will be drain terminal and
here there will be source terminal
now in this if my input is logic 1
means if g is equals to 1 this nmos
that will be on and if this
gate is at logic 0 we can say this nmos
that will be off and
if you talk about pmos then
you see in pmos here there will be
bubble
with gate and here
you see this terminal will be source
terminal and this terminal will be
drain terminal right so you see with
this pmos
here we have source
and here we have drain
while this with this nmos here there
will be
drain terminal and here there will be
source terminal
with this q4 this is drain and this is
source
and in this pmos if gate is equals to
logic 0 in that case
this pmos will be on and if gate is
equals to
1 in that case this pmos will be
off what is the meaning of on
on means it will be having short circuit
over here
and what will be the meaning of off
there will be open circuit over here
right now let us consider
this input and how output is coming
that we will be observing in this
circuit so if my input
is 0 0 in that case
you see a and b both are 0
so pmos that will be on
and nmos that will be off so as this
pmos
is on this q1 and q2
that will be on and this q3 and q4
that will be off
and as per that you see my output that
will be vdd
means we can say it is logic 1
right let us have second case with a
and b if a is 0 and b is 1
then you see a is connected with q1 and
q3 so q1 is pmos so if
a is 0 this pmos is on
and this q3 is nmos so it will be
off so this is on
and this is off and you see b is one
so b is one means p mos is one so q two
that will be off and
q four is having input b so b is one
so it will be on so this is q4 that is
on
and this will be off so now you see
this is on right so
here output will be vdd and this is off
so your output is vdd and
that is referred as logic one
now let us have third case so that is
one zero
so in that if you see pmos then
here see a is connected with q one
that is one so it will be off
and this b is connected with q two so
that is p motion b is zero so it will be
on
[Music]
and here q3 is connected with nmos
and here a is 1
so q3 will be
on and
this q4 that is nmos and that is having
input 0 so it will be off
so now you see again output will be vdd
as this is open circuit so
output will be vdd means logic one
now if input a and b both are one one
then you see a and b both both are
having one
input and those are pmos with
q one and q2 so that will be off
and q3 and q4 both are nmos and
input is logic 1 means both are on and
as both
are on output will be ground
means logic 0. so this is how
complete circuit functions with cmos
nand gate
i hope that you have understood this
video please do give your valuable
suggestions the reason is your
suggestions matters to me and based on
that in future
i'll be making videos which will be
resolving your queries
so please do give your valuable
suggestions thank you so much for
watching this video
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