keith1200rs said:The easiest way is with some design software, particularly if you want to check the sensitivity of the design to component tolerances. I don't know of any free software that will do 7th order, although there may be some. I use Nuhertz Filter Solutions which is pretty good (but expensive). I may have useful data in my filter design books if you give me the passband ripple you want.
Keith.
LvW said:However, one exception just comes into my mind: Filter solutions (Nuhertz tech.) is able to design active ladder structures.
keith1200rs said:Yes, that is why I bought the software! I assume this is the sort of design you are looking for?
Keith.
abbey said:Thank you very much!They were really flexible about the ripple and cut-off frequency.So I can choose any of these.I do have a spice simulator so I could run any schedule.However,i chose to use a sallen-key topology.I hope that it's not a bad choice.
marcovaldo2000 said:@ FvM
I agree. But I concern about the ability to simulate the parasitic impedance with PSPICE, plus I also need to incorporate a gain stage right after that. I was thinking using active filter that may simplify the design.
By the way, that is for a 0.3dB p-p ripple LPF.
keith1200rs said:marcovaldo2000 said:@ FvM
I agree. But I concern about the ability to simulate the parasitic impedance with PSPICE, plus I also need to incorporate a gain stage right after that. I was thinking using active filter that may simplify the design.
By the way, that is for a 0.3dB p-p ripple LPF.
Pspice has the ability to simulate it, the tricky part is creating all the models for all the parts!
Sallen Key is not the way to go. The bandwidth requirements are crazy.
Here is a GIC Ladder implementation.
I have to say though, I agree with other comments that you should look at passive. I have used quite a few 1GHz to 2GHz opamps but I have never tried making filters with them and I'm not sure they would be ideal. Still, you could easily simulate it first.
I have done 5 & 6 pole Cheby LP with LC and they have worked fine. I seem to remember the tricky bit is the inductor series resistance can be a problem so you may need to tweak some values to get back to the right response. And you have to watch out for tolerances of course, but that is true for any high order filter.
Keith.
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