# Noise Margin for CMOS

#### zulfi100

Joined Jun 7, 2012
656
Hi,
Can some body plz guide me with the following question:
What is the high level noise margin of CMOS 5v series circuit?
I dont know whether i have to use a foprmula to solve this question or its just a fixed value which i have to remember. I have found some values in the following link:
http://www.interfacebus.com/Logic_Family_Noise_Margin.html

but it doesnt say about series or parallel.

Kindly guide me.

Zulfi.

#### WBahn

Joined Mar 31, 2012
27,478
The HI level noise margin is basically the difference between the lowest HI value that an output is guaranteed to produce and the lowest HI value that an input is guaranteed to recognize.

#### zulfi100

Joined Jun 7, 2012
656
Hi,
Noise Margine High=4.9-3.985=0.915v

Zulfi.

#### WBahn

Joined Mar 31, 2012
27,478
Hi,
Noise Margine High=4.9-3.985=0.915v

Zulfi.

I don't know where you are getting those numbers from. It isn't from the table on the page you linked to.

That page tells you exactly how to calculate the noise margin and tabulates the results for many different families. What, exactly, are you asking about that is not clear from that page?

#### zulfi100

Joined Jun 7, 2012
656
Hi,
Sorry for not clarifying you.
My question is:
What is the high level noise margin of CMOS 5v series circuit?
This is the question. I dont have any other data other than CMOS 5v series circuit. Is it possible to calculatye high level noise margin?

From the site i got following for CMOS 5v:
VOH VIH Margin VIL VOL Margin
4.9v 3.85v 1050mV 1.35v 0.1 1340mV
The HI level noise margin is basically the difference between the lowest HI value that an output is guaranteed to produce and the lowest HI value that an input is guaranteed to recognize.
I calculated noise margin by subtracting VOH & VIH i.e (4.9-3.85)
Thanks for your interest in my problem.

Zulfi.

Last edited:

#### WBahn

Joined Mar 31, 2012
27,478
I calculated noise margin by subtracting VOH & VIH i.e (4.9-3.85)
But look at your post #3:

Noise Margine High=4.9-3.985=0.915v
That you got a value different from the 1050mV given in that same table should have set off warning bells.

But it's clear you understand the concept, which is what is important.

#### zulfi100

Joined Jun 7, 2012
656

Zulfi.