Ok, I know bandpass filters or bandstop filters are normally made with a capacitor and inductor in series or parallel, but would it be possible to make one with 2 RC filters? One would be highpass, the other would be lowpass. This seems like an extremely elegant solution, so the fact that i don't see it often tells me there's probably some really fundamental error that i'm missing. what is it?

 

Hello,

Here is a PDF on filter design with opamps.
In there is a comparisson of band filters with high/low pass combinations.
With opamps you will hardly use inductors.

Greetings,
Bertus

 

Hello,

Here is a PDF on filter design with opamps.
In there is a comparisson of band filters with high/low pass combinations.
With opamps you will hardly use inductors.

Greetings,
Bertus

i've done active filters, i'm looking for a passive filter. and i would like to understand WHY this particular one is not used.

 

i've done active filters, i'm looking for a passive filter. and i would like to understand WHY this particular one is not used.

Design one and plot the response curves. I think it will be clear why it isn't done.

 

Design one and plot the response curves. I think it will be clear why it isn't done.

I would've done that already, however i do not have any simulation software, nor do i have any tangible frequency response measurement devices. Maybe you could point me in the right direction with regards to software (free, preferably)?

 

You might try LT Spice:

http://www.linear.com/designtools/software/ltspice.jsp

 

You might try LT Spice:

http://www.linear.com/designtools/software/ltspice.jsp

thanks. just downloaded it

now i'm tryin to overcome this learning curve b/f i can get anything useful done

 

This would be a good opportunity for you to learn how to analyze the circuit you propose without using simulation software. It is a valuable skill to learn if you have an interest in comparing different filter topologies.

There was a time when there was no simulation software. Once you have analyzed a filter yourself you will have a deeper appreciation for filters as well as simulation software.

hgmjr

 

Hello,

When connecting RC low and highpass filters together you will find out that the second filter acts as a frequency dependend load to the first one.
In other words they interact with eachother and give an other frequency curve as expected.
A great deal of this interaction can be solved by placing buffers between the filters.
This can be transistors or opamps.

Greetings,
Bertus