[IC opamp testing question] help!!

[ee484]

Hi, all.

I'm currently testing a opamp with unity gain feedback.

With small DC input (<30mV), it seems that it does not have any problem.
However, as DC input increases, the output of the opamp (unity gain feedback) has oscillation and it is proportional to the input amplitude.

Since it does oscillate with DC input, I don't think it comes from lack of phase margin..

What's the typicall senario that cause this oscillation in a testing? The oscillation frequency is about 1.2MHz.

If I put 1MHz cutoff freq. low pass filter, it does it's job.

Thanks...


Best.

B

 

[A.Anand Srinivasan]

check ur opamp datasheet.... if my guess is right ur opamp is an uncompensated one.... these kinds of opamp are not internally compensated and have problem at unity feedback...