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SSPD_Chapter 7_Part 6_Basic Circuit Concepts_continued 3 calculates the rise time and the fall timne and proves that for symmetric switching PMOS width must be 2.5 times wider than NMOS width.

SSPD_Chapter 7_Part 6_Basic Circuit Concepts_continued 3

7.6.4. Formal Estimation of CMOS Inverter delay.

In Figure we show a CMOS Inverter being driven by square wave and loaded with input capacitance of the subsequent stage. We model the CMOS Inverter during switching transients by constant current source driving the load capacitance.

The switching transient is shown in Figure

As can be seen in Figure, during HIGH to LOW switching NMOS (Q n ) provides the low impedance path to ground and hence sinks the discharge current. Hence saturation current of NMOS provides the I D .

Similarly during LOW to HIGH switching PMOS (Q p ) provides the low impedance path from V DD bus to the load capacitance and hence sources the charging current. Hence saturation current of PMOS provides the I C .

Referring to the circuit model in Figure we see that:

Rate of change of capacitance voltage = Constant Current/C




During output HIGH to LOW transient: NMOS (Q n ) is sinking the current from the load capacitance hence constant current source is a discharge current I D coming as the saturation current of NMOS where

During output LOW to HIGH transient:PMOS(Q p ) is sourcing the current to the load capacitance hence constant current source is a charging current I C coming as the saturation current of PMOS where

But ∆V C = V DD , V GS = V DD and V T = 0.2 V DD therefore

Substituting Eq. in Eq and Eq. we get:

Dividing Eq by Eq. we get:

From Basic Electrical Properties we know that

From Device Physics we know that

We also know from section 7.3.12 titled ‘optimization of geometric parameters to achieve the beswt CMOS performance’ that :

Substituting the two conditions stated by Eq. and Eq. in Eq we get

Eq implies that we will get symmetric switching transients as well as maximum Noise Margin if satisfy the condition stated in Eq namely

Hence CMOS layout will be as shown in Figure for optimum performance in all sense of the word i.e in the sense of switching transient and in the sense of noise margin.

Two alternative layouts are shown in Figure

In all the three figures, where metal has to connect to Poly-Si or to n-channel or to p-channel there a contact has to be made symbolized by black cross.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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