samiran_dam
Full Member level 2
Dear All,
Does anybody have any experience such that while designing an Sallen-key active filter you encountered a situation like this -
I. I am simulating a 2nd order butterworth filter designed using SK topology.
II. using ideal opamp I ma getting accurate transfer characteristic - i.e. calculated complex-conjugate pole ans thus Q-factor.
III. But after adding two poles to the opamp's transfer function [I have ensured that ugf > 100*fiter's bandwidth] making poles moving towards RHP. This is happening if Second pole is situated far away but, if second pole is moved closer to the UGF, filter pole's are becoming closer to the ideal.
I am confused! I am using opamp model which is verified to give correct open-loop and closed loop frequency response and transient response.....(thus I guess there is no problem in OPAMP's model at least).
Please help! Please let me know if you need further clarification.
Regards
Samiran.
Does anybody have any experience such that while designing an Sallen-key active filter you encountered a situation like this -
I. I am simulating a 2nd order butterworth filter designed using SK topology.
II. using ideal opamp I ma getting accurate transfer characteristic - i.e. calculated complex-conjugate pole ans thus Q-factor.
III. But after adding two poles to the opamp's transfer function [I have ensured that ugf > 100*fiter's bandwidth] making poles moving towards RHP. This is happening if Second pole is situated far away but, if second pole is moved closer to the UGF, filter pole's are becoming closer to the ideal.
I am confused! I am using opamp model which is verified to give correct open-loop and closed loop frequency response and transient response.....(thus I guess there is no problem in OPAMP's model at least).
Please help! Please let me know if you need further clarification.
Regards
Samiran.