Probably the Q is too high. BPF designs can make very good oscillators. ----- Original Message ----- From: "Mike Hord" To: Sent: 07 May 2003 15:27 Subject: [EE]: Oscillatory behaviour in a BPF > It boggles the mind. > > I have a program called FilterFree. It purports to take the grunt work out > of designing low-order analog filters. I'm trying to design a 1st order > Butterworth BPF, centered at 60 kHz with BW +/- 2kHz. When I add in the 3rd > stage of the filter design (which looks okay to me) provided by FilterFree, > instead of a BPF, I get a BEAUTIFUL (I mean, you could market this thing) 57 > kHz sine wave, regardless of the input to the filter. > > My op-amps seem to be working (at least, I can implement simple voltage > follower and amplifier circuits with them), and I was wondering if anyone > else has ever encountered this problem, or has any opinion about FilterFree. > > No, I'm not going to try to ASCII art the circuit. It's a little more than > I want to attempt. If anyone really wants to see it, let me know and I'll > post it on my website tomorrow. It really is a good sine wave generator; > the sine wave it generates is actually a bit more stable than the one my > signal generator is coming up with. > > Mike H. > > _________________________________________________________________ > Help STOP SPAM with the new MSN 8 and get 2 months FREE* > http://join.msn.com/?page=features/junkmail > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads