The Designer's Guide Community
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Jul 14th, 2020, 10:54pm
Pages: 1
Send Topic Print
Output swing, threshold voltage and body effect (Read 447 times)
Junior Member

Posts: 30
Output swing, threshold voltage and body effect
Jan 08th, 2019, 10:04am
I have some questions regarding output voltage swing, it's relationship to the input common voltage and the threshold voltage. In the attached figure the output voltage can swing between Vout,max_swing = VDD - ISS/2 * RD (where ISS/2 is the current when the input differential voltage is zero) and Vout,min_swing= VIC - VTH.

So it follows that having a high VIC is detrimental to swing in both directions because increasing VIC increases the current and the voltage drop across RD, decreasing Vout,max_swing. A high VIC increases Vout,min_swing as well.

Now if we had diff. pair where the NMOS transistors had their own isolated pwells so that the source and bulk can be tied together. This prevents the VTH from increasing and the required bias VIC from increasing.

So is my reasoning right, here?

If we have an input diff pair in isolated wells, besides helping with PSRR or substrate noise, it also helps with output swing(?).

if we can afford the space, does tying the source and bulk of input diff pair increase the output swing?

Back to top
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2020 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 Consider submitting a paper or model.