Hi all,


i'm designing an active RC filter. I have not yet added compensation to the opamp, but I was wondering if there is any need to. The op amp is after all used in a filter where the caps and R's determine the phase shift and gain in the closed loop. So anyway my second question is, is there a way to do a closed-loop stability check?

thanks,
aaron

Hi Aaron,

I would think you still need to add compensation to the opamp. The reason is that the frequencies at which your RC filter will be will behave as such should be lower than the ones at which the opamp introduces significant phase shifts (opamp poles).  In other words: the frequencies associated with the RC closed loop phase shifts should be such that the opamp open loop gain is large enough. Therefore opamp open loop gain singularities should be at higher frequencies than the RC time constant.
Loop stability should be guaranteed by setting the dominant pole in the opamp open loop gain, which cannot be guaranteed if the requirement mentioned above is fulfilled.

Hope this helps
Tosei.