| Electronics > Projects, Designs, and Technical Stuff |
| Active filter design : 2nd order sharp roll-off |
| (1/6) > >> |
| Rutherberg:
Hello, All is in the subject, I have a hard time to design a non-inverting 2nd order high pass with a sharp roll-off. I would like to keep the -40db/decade, but with a sharper roll-off. With a classic 2nd order, the roll-off is too slow. What type of filter should I use for these results ? Thanks |
| Conrad Hoffman:
2nd order is only good for so much. You need a higher order filter. |
| T3sl4co1l:
Yeh... how sharp are you looking for? Consider this: you only gave one number, and it's not even the property you're trying to optimize! That doesn't give us much to go on. How much peaking can you tolerate? That's the only variable you have control over. To get a sharper cutoff, you need a higher order filter, even if you don't need the cutoff attenuation that gives. If you can afford an elliptical filter, it can be much sharper, but it will likely take more parts, or more order (there's hardly such a thing as an elliptical 2nd order), though it can still have the same asymptote. Mind that, if this is an active filter, the attenuation may level off anyway, due to the amp's finite gain. Tim |
| Benta:
Look into Chebyschev filters. They have a sharper initial rolloff, but end at -40 dB/decade. Downside is, you'll have ripple/peaking in the pass band. |
| Rutherberg:
Ok thanks, I may have found a hint of what I try to achieve. Attached, an op amp circuit with a transistor gyrator. The curve of the peak is what I want. The idea now is to keep same gain at peak frequency after the peak frequency, to make a high pass filter, thus the roll-off will be fast. I don't know if I'm clear. How can I achieve this ? |
| Navigation |
| Message Index |
| Next page |