Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Question regarding filters?

Status
Not open for further replies.

mohideen

Member level 2
Joined
Jan 19, 2011
Messages
45
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,580
Hi all,

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

Thanks in advancer.
 

immadi.jagadish

Member level 5
Joined
Dec 19, 2010
Messages
90
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,830
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?
 

zorro

Advanced Member level 4
Joined
Sep 6, 2001
Messages
1,131
Helped
356
Reputation
710
Reaction score
298
Trophy points
1,363
Location
Argentina
Activity points
8,903
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
 

mohideen

Member level 2
Joined
Jan 19, 2011
Messages
45
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,580
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.
 

zorro

Advanced Member level 4
Joined
Sep 6, 2001
Messages
1,131
Helped
356
Reputation
710
Reaction score
298
Trophy points
1,363
Location
Argentina
Activity points
8,903
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
 

keith1200rs

Super Moderator
Staff member
Joined
Oct 9, 2009
Messages
10,877
Helped
2,064
Reputation
4,128
Reaction score
1,597
Trophy points
1,403
Location
Yorkshire, UK
Activity points
57,276
If you are trying to filter audio then you would normally exclude very low frequencies below say 300Hz or 100Hz.

Keith
 

mohideen

Member level 2
Joined
Jan 19, 2011
Messages
45
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,580
In that case, if I am to exclude frequencies up to 300 Hz, I have to use a bandpass filter right?
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,835
Helped
1,740
Reputation
3,484
Reaction score
1,340
Trophy points
1,393
Location
Germany
Activity points
39,237
In that case, if I am to exclude frequencies up to 300 Hz, I have to use a bandpass filter right?
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.
 

andre_teprom

Super Moderator
Staff member
Joined
Nov 7, 2006
Messages
9,201
Helped
1,142
Reputation
2,303
Reaction score
1,119
Trophy points
1,403
Location
Brazil
Activity points
53,591
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.


+++
 

mohideen

Member level 2
Joined
Jan 19, 2011
Messages
45
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,580
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.
 

zorro

Advanced Member level 4
Joined
Sep 6, 2001
Messages
1,131
Helped
356
Reputation
710
Reaction score
298
Trophy points
1,363
Location
Argentina
Activity points
8,903
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
 

cent24.3

Member level 2
Joined
Jul 14, 2004
Messages
46
Helped
4
Reputation
8
Reaction score
3
Trophy points
1,288
Activity points
304
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
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,835
Helped
1,740
Reputation
3,484
Reaction score
1,340
Trophy points
1,393
Location
Germany
Activity points
39,237
Well, I have to filter 0-3KHz (Voice) ........
What does this mean? Passband between 0 and 3 kHz? What is the purpose of the filter (see Zorro's posting)?
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top