[SOLVED] Why do we need to check stability of open-loop OPAMP

Status
Not open for further replies.
C

CHL

Member level 3
Joined
Jan 20, 2015
Messages
60
Helped
2
Reputation
4
Reaction score
2
Trophy points
8
Activity points
550
Hello

Stability issue occurs only when there is a feedback in an amplifier.

If an OPAMP works in open-loop, there isn't the stability problem.

However, when we design an OPAMP, we consider the phase margin and gain margin although there isn't a feedback initially (we may include a feedback path after designing the amp).

What is the reason?

Is it for the general use of the OPAMP? (ex, any feedback loop can be added to make a feedback amp, such as a buffer by connecting the input and output directly)

Thanks
 

Yes - you are right. An amplifier without feedback cannot be unstable (however, a high-gain opamp is in saturation due to offset voltages - another problem).
But it is common practice to check if an amplifier will be stable - after feedback is applied. The most critical case is 100% feedback (closed-loop unity gain application).
Therefore, the stability margin of the open-loop gain Aol is determined because for 100% feedback the loop gain (which matters only for stability) is LG=Aol*1=Aol.
 
Reactions: CHL

    C

    CHL

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…