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Discussion Groups | Comp.DSP | butterworth filter on pcb?


There are 5 messages in this thread.

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butterworth filter on pcb? - Russ - 2007-07-05 07:42:00

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


Re: butterworth filter on pcb? - Scott Seidman - 2007-07-05 08:35:00

Russ <r...@tva.gov> 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


Re: butterworth filter on pcb? - Jerry Avins - 2007-07-05 09:43:00

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.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯


Re: butterworth filter on pcb? - Clay - 2007-07-05 09:54:00

On Jul 5, 7:42 am, Russ <rwpatter...@tva.gov> 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


Re: butterworth filter on pcb? - Vladimir Vassilevsky - 2007-07-05 10:59:00

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