The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Mar 29th, 2024, 12:01am
Pages: 1
Send Topic Print
Basic Question : NMOS Switch on-resistance Versus Input Voltage Figure (Read 3445 times)
allenhan
New Member
*
Offline



Posts: 1

Basic Question : NMOS Switch on-resistance Versus Input Voltage Figure
Sep 29th, 2015, 9:31am
 
It is quite a basic question, I wanna draw the nmos switch on-resistance versus the input voltage figure. Here is what I have done so far. nmos gate is 3.3V, and the input voltage is a DC sweeping voltage ( I suppose it is from 0 to 3.3V), and the at the output node of the nmos, I put a holder cap to the ground also. So based on this model I wanna draw the Ron VS. Input Voltage figure.

I tried to use the XL calculator to calculate it, like, Ron =( Vin-Vout )/In,  but compared to the real value in the DC operating point report,  the calculator doesnt give a good number. and also which is strange, the when input is 500mV, for example, I plot the S node and D node current of nmos, but the currents are not same.....confuse me.

Any way, I think I saw some options on web, but not really accurate and neat, so I want to ask again, is there a good way, in cadence to draw the continuous figure line Ron VS. Vin.   Thanks.
Back to top
 
 
View Profile   IP Logged
RobG
Community Fellow
*****
Offline



Posts: 569
Bozeman, MT
Re: Basic Question : NMOS Switch on-resistance Versus Input Voltage Figure
Reply #1 - Sep 30th, 2015, 7:48am
 
Are you applying an "In" or just looking at leakage? How much is the difference between the source and drain current?

I apply an Iin using a DC current source so that Vds is ~10mV then plot Vds/Iin. You could also do a parametric sweep and plot gds using the OP function in the calculator.
Back to top
 
 
View Profile   IP Logged
DanielLam
Community Member
***
Offline



Posts: 76

Re: Basic Question : NMOS Switch on-resistance Versus Input Voltage Figure
Reply #2 - Oct 1st, 2015, 11:36pm
 
This page has the setup for Ron. I've used it hundreds of times. Look for on-resistance of a switch. You can do a parametric sweep of W/L versus Vcm.

If you get an impedance, take the real part of it to get resistance.

http://web.engr.oregonstate.edu/~moon/kaj/cadence.html
Back to top
 
 
View Profile   IP Logged
sheldon
Community Fellow
*****
Offline



Posts: 751

Re: Basic Question : NMOS Switch on-resistance Versus Input Voltage Figure
Reply #3 - Oct 5th, 2015, 7:54pm
 
Why don't you just plot input voltage against the gds value, the
real value, from the dc operating point? Right now, you are just
dividing 0/0.
Back to top
 
 
View Profile   IP Logged
A Kumar R
Community Member
***
Offline



Posts: 72
India
Re: Basic Question : NMOS Switch on-resistance Versus Input Voltage Figure
Reply #4 - Oct 6th, 2015, 1:38am
 
Hi,

Can you give a drawing of what you are trying to do? i am not getting where is Vin , Vout and all those notations you have used.

Regards
Anil Reddy
Back to top
 
 
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2024 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.