I was recently trying to design a LPF using the filter wizard. My passband frequency is 20Hz (-3dB attenuation) and my stopband frequency is 80kHz (-80dB attenuation). I keep getting "No opamp found that meets the requirement". I want a design optimized for low noise and the only time I am able to get that is when I increase the passband frequency to about 110Hz. Is there some fundamental issue when the difference between the passband and stopband frequencies are so high? What is the cause for the design tool saying "No opamp found that meets the requirement"?
[edited by: mohan at 8:08 AM (GMT 0) on 10 Aug 2020]