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Question regarding filters?

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mohideen

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Hi all,

Must I use a bandpass filter for a base-band signal?

Thanks in advancer.
 

band pass filter is obviously combination of LPF and HPF,so,you can design these with required SPECifications for base band signals.
Anyway,Why you are looking for other than band pass filter?
 

Hi Hohideen,

you shuold be more specific. What type of baseband signal have you? What is the goal of filter that signal?
At first glance, it seems that the answer at your question should be "no", but it depends upon the situation.

@ immadi.jagadish: it is wrong that "band pass filter is obviously combination of LPF and HPF". Think in the diagrams of poles & zeros of selective passband filters and you will see that they are not a cascade of low-pass and high-pass.

Regards

Z
 

Well, sorry for being not specific.
My goal is to pass through signals between 0-3KHz.
I believe a 2nd order sallen-key low pass filter would be the best solution.
However I was thinking should i consider a bandpass filter or stick with my initial idea which is the sallen key filter?

Thanks.
 

The band of your signal starts from 0 Hz.
A bandpass filter would reject low frequencies in this band.
Why do you think a passband filter can be good?
Regards

Z
 
If you are trying to filter audio then you would normally exclude very low frequencies below say 300Hz or 100Hz.

Keith
 

In that case, if I am to exclude frequencies up to 300 Hz, I have to use a bandpass filter right?
 

mohideen said:
In that case, if I am to exclude frequencies up to 300 Hz, I have to use a bandpass filter right?
Click to expand...

Yes, and for your information and clarification: Sallen&Key is the name for an active filter structure based on opamps with finite gain that can be used to realize lowpass AND bandpass responses as well.
 

Know the application is important to aid decision.

For instance, for telephony, it is acceptable to cut low band frequencies by a bandpass filter.
However, to high fidelity applications ( i.e. music ) should be better to choose lowpass filter.


+++
 

Well, I have to filter 0-3KHz (Voice) and feed it into an audio amplifier... Which filter can be the best solution, low pass or band pass and why?
Thanks.
 

More generally, in order to decide not only the type of filter but also its characteristics, it is necessary to say: why do you need to filter the signal?
You could feed directly the amplifier without filtering, right?

Do you need to suppress high-frequency noise? Do you need to suppress low-frequency spurious signals? Do you need to limit the band for ADC coversion? etc...
Regards

Z
 

Hi mohidden,
I think all is there. It's up to you.
But for cost reason I would use in this case a low pass filter (a 1st order passive RC filter) plus a hi-pass filter (an other 1st order passive RC) separated by a one gain (or more) op-amp.
Of course it depends how fast you want to cut unwanted frequencies...

good luck
 

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