butterworth filter on pcb?

Started by Russ July 5, 2007
Hi:

I've built a simple 2-pole low-pass Butterworth filter (maximally flat
magnitude filter) with a cutoff frequency of 1kHz.  I built it out of
741 op-amps and capacitors/resistors.

What i want to know is this - can i buy a prefabricated filter like
this that i can plug into a printed circuit board?   I'd like to make
several of my circuits but i'd rather not totally rebuild the filter
each time if i can get a simple plug in module that will perform that
filter function satisfactorily.

thanks,
russ

Russ  wrote in news:1183635779.361297.79970@
57g2000hsv.googlegroups.com:

> Hi: > > I've built a simple 2-pole low-pass Butterworth filter (maximally flat > magnitude filter) with a cutoff frequency of 1kHz. I built it out of > 741 op-amps and capacitors/resistors. > > What i want to know is this - can i buy a prefabricated filter like > this that i can plug into a printed circuit board? I'd like to make > several of my circuits but i'd rather not totally rebuild the filter > each time if i can get a simple plug in module that will perform that > filter function satisfactorily. > > thanks, > russ > >
Yes. There are a number of approaches, depending upon what you need to do and what you're willing to spend. There are inexpensive clocked filters that often need some external passive components, but less than would be required by your op-amp design. They will be more accurate in cutoff, as the design won't depend on 20% tolerance capacitors. The drawback is there are still extra components, you need a clock generator, and there is usually clock feedthrough to worry about. There are also analog chips. Burr Brown used to make a bunch of them. I believe TI has picked up the line. Search for the TI UAF42, for example. These are more expensive than clocked filters, often, but still reasonable. There are also some high-pole analog filters available from places like Frequency Devices. I love them and use them, but they're >$100 each! -- Scott Reverse name to reply
Russ wrote:
> Hi: > > I've built a simple 2-pole low-pass Butterworth filter (maximally flat > magnitude filter) with a cutoff frequency of 1kHz. I built it out of > 741 op-amps and capacitors/resistors. > > What i want to know is this - can i buy a prefabricated filter like > this that i can plug into a printed circuit board? I'd like to make > several of my circuits but i'd rather not totally rebuild the filter > each time if i can get a simple plug in module that will perform that > filter function satisfactorily.
You can get switched-capacitor filters in small DIPs. Burr-Brown used to make them and may still. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
On Jul 5, 7:42 am, Russ  wrote:
> Hi: > > I've built a simple 2-pole low-pass Butterworth filter (maximally flat > magnitude filter) with a cutoff frequency of 1kHz. I built it out of > 741 op-amps and capacitors/resistors. > > What i want to know is this - can i buy a prefabricated filter like > this that i can plug into a printed circuit board? I'd like to make > several of my circuits but i'd rather not totally rebuild the filter > each time if i can get a simple plug in module that will perform that > filter function satisfactorily. > > thanks, > russ
Russ, Start here: http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1008,D4145 Clay

Jerry Avins wrote:


> > You can get switched-capacitor filters in small DIPs. Burr-Brown used to > make them and may still.
Maxim does it too. However the dynamic range of those filters is only about 70dB. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com

Jerry Avins wrote:


> > You can get switched-capacitor filters in small DIPs. Burr-Brown used to > make them and may still.
Maxim does it too. However the dynamic range of those filters is only about 70dB. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
On Jul 5, 7:42 am, Russ  wrote:
> Hi: > > I've built a simple 2-pole low-pass Butterworth filter (maximally flat > magnitude filter) with a cutoff frequency of 1kHz. I built it out of > 741 op-amps and capacitors/resistors. > > What i want to know is this - can i buy a prefabricated filter like > this that i can plug into a printed circuit board? I'd like to make > several of my circuits but i'd rather not totally rebuild the filter > each time if i can get a simple plug in module that will perform that > filter function satisfactorily. > > thanks, > russ
Russ, Start here: http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1008,D4145 Clay
Russ wrote:
> Hi: > > I've built a simple 2-pole low-pass Butterworth filter (maximally flat > magnitude filter) with a cutoff frequency of 1kHz. I built it out of > 741 op-amps and capacitors/resistors. > > What i want to know is this - can i buy a prefabricated filter like > this that i can plug into a printed circuit board? I'd like to make > several of my circuits but i'd rather not totally rebuild the filter > each time if i can get a simple plug in module that will perform that > filter function satisfactorily.
You can get switched-capacitor filters in small DIPs. Burr-Brown used to make them and may still. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Russ  wrote in news:1183635779.361297.79970@
57g2000hsv.googlegroups.com:

> Hi: > > I've built a simple 2-pole low-pass Butterworth filter (maximally flat > magnitude filter) with a cutoff frequency of 1kHz. I built it out of > 741 op-amps and capacitors/resistors. > > What i want to know is this - can i buy a prefabricated filter like > this that i can plug into a printed circuit board? I'd like to make > several of my circuits but i'd rather not totally rebuild the filter > each time if i can get a simple plug in module that will perform that > filter function satisfactorily. > > thanks, > russ > >
Yes. There are a number of approaches, depending upon what you need to do and what you're willing to spend. There are inexpensive clocked filters that often need some external passive components, but less than would be required by your op-amp design. They will be more accurate in cutoff, as the design won't depend on 20% tolerance capacitors. The drawback is there are still extra components, you need a clock generator, and there is usually clock feedthrough to worry about. There are also analog chips. Burr Brown used to make a bunch of them. I believe TI has picked up the line. Search for the TI UAF42, for example. These are more expensive than clocked filters, often, but still reasonable. There are also some high-pole analog filters available from places like Frequency Devices. I love them and use them, but they're >$100 each! -- Scott Reverse name to reply
Hi:

I've built a simple 2-pole low-pass Butterworth filter (maximally flat
magnitude filter) with a cutoff frequency of 1kHz.  I built it out of
741 op-amps and capacitors/resistors.

What i want to know is this - can i buy a prefabricated filter like
this that i can plug into a printed circuit board?   I'd like to make
several of my circuits but i'd rather not totally rebuild the filter
each time if i can get a simple plug in module that will perform that
filter function satisfactorily.

thanks,
russ