how to tell if opamp is unity gain stable

[panfilero]

hello,

does anyone know how to tell if an opamp is unity gain stable? My guess isto check out the open loop phase margin and make sure it's over... I dunno.... about 30 degrees... is this it? Don't most opamps have decent open loop phase margin? Should I be saying open loop phase margin or does just saying phase margin imply that you are talking about the open loop phase margin of the opamp?

much appreciate your comments!

 

[[email protected]]

hello,



does anyone know how to tell if an opamp is unity gain stable? My guess is to check out the open loop phase margin and make sure it's over... I dunno... about 30 degrees... is this it? Don't most opamps have decent open loop phase margin? Should I be saying open loop phase margin or does just saying phase margin imply that you are talking about the open loop phase margin of the opamp?



much appreciate your comments!

"open loop phase margin" is an oxymoron, the very term phase margin is partand parcel with feedback, how you could possibly have feedback in a open loop???

 

[brent]

hello,

does anyone know how to tell if an opamp is unity gain stable?  My guess is to check out the open loop phase margin and make sure it's over... I dunno... about 30 degrees... is this it?  Don't most opamps have decent open loop phase margin?  Should I be saying open loop phase margin or does just saying phase margin imply that you are talking about the open loop phase margin of the opamp?

much appreciate your comments!

This is a strange post. Your question shows that you know enough
about this to not need an answer from anyone. Secondly, just how much
does anyone really worry about unity gain stability in op amps
anymore? It seems that every op made for the last 20 years is unity
gain stable.

 

[josephkk]

But the phase margin isn't equal to any phase you measure on the
closed-loop system--especially if it's negative. It's inherently an
open-loop quantity, which is why nobody says "open loop phase
margin"--it would be redundant.

Cheers

Phil Hobbs

The concept is useful in all cases. That aspect related to the
definition. It can be measured and used both open and closed loop.

?-)