| Author |
Message |
Viram
Guest
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 Posted:
Fri Feb 11, 2005 5:05 pm Post subject:
Low pass filter, cut off 500 Hz, short response time... |
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I'm trying to design a LP-filter with a cut off at around 500 Hz. My
problem is getting a short response time and low/no resonance peak. What
order should the filter be? I'm currently trying with a simple
LC-filter...
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lloyd
Guest
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| Posted:
Fri Feb 11, 2005 6:54 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
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Viram escribió:
| Quote: | I'm trying to design a LP-filter with a cut off at around 500 Hz. My
problem is getting a short response time and low/no resonance peak. What
order should the filter be? I'm currently trying with a simple
LC-filter...
When you design a LP filter, actually you are limiting the response |
time. For 500Hz the time constant is about 0.3 msec.
If you want to limit the resonance peac, you can share the capacitor in
some smaller parallel units and put one resistor in series with one of
them. |
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Don Pearce
Guest
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| Posted:
Fri Feb 11, 2005 7:02 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
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On Fri, 11 Feb 2005 13:54:34 +0100, lloyd <me@private.net> wrote:
| Quote: | Viram escribió:
I'm trying to design a LP-filter with a cut off at around 500 Hz. My
problem is getting a short response time and low/no resonance peak. What
order should the filter be? I'm currently trying with a simple
LC-filter...
When you design a LP filter, actually you are limiting the response
time. For 500Hz the time constant is about 0.3 msec.
If you want to limit the resonance peac, you can share the capacitor in
some smaller parallel units and put one resistor in series with one of
them.
|
No, the resonance peak is down to the style of filter. Generally a
Chebyshev will be bad, a Butterworth somewhat better and a Gaussian
has no peak. You pay a price for the lack of resonance in a droopier
response around the corner frequency.
d
Pearce Consulting
http://www.pearce.uk.com
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Guest
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| Posted:
Fri Feb 11, 2005 8:35 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
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Viram wrote:
| Quote: | I'm trying to design a LP-filter with a cut off at around 500 Hz. My
problem is getting a short response time and low/no resonance peak.
What
order should the filter be? I'm currently trying with a simple
LC-filter...
|
You need to get hold of a decent text on filter design - I use the
"Electronic Filter Design Handbook" by Arthur B. Williams and Fred J.
Taylor - ISBN 0-07-070434-1. Since then there has been a third edition
(ISBN 0-07-070430-9) which is supposed to be even better, but it seems
to be out of print - www.amazon.com offers three second hand copies for
about $130. You should be able to find it - or something very like it -
in a university library.
The usual choice for what you seem to want to be doing is a
"linear-phase" or "Bessel filter", though a "synchronously tuned"
filter (consisting of identical multiple poles) actually gives fastest
settling for a given number of poles, with the step getting to better
than 99% after five time constants. Adding more poles makes the step
steeper at the 50% point, and pushes the 50% point back from around one
time constant at one pole to closer to three at ten poles.
A simple LCR filter is two poles ...
---------
Bill Sloman, Nijmegen |
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Don Lancaster
Guest
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| Posted:
Fri Feb 11, 2005 10:11 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
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bill.sloman@ieee.org wrote:
| Quote: | Viram wrote:
I'm trying to design a LP-filter with a cut off at around 500 Hz. My
problem is getting a short response time and low/no resonance peak.
What
order should the filter be? I'm currently trying with a simple
LC-filter...
You need to get hold of a decent text on filter design - I use the
"Electronic Filter Design Handbook" by Arthur B. Williams and Fred J.
Taylor - ISBN 0-07-070434-1. Since then there has been a third edition
(ISBN 0-07-070430-9) which is supposed to be even better, but it seems
to be out of print - www.amazon.com offers three second hand copies for
about $130. You should be able to find it - or something very like it -
in a university library.
The usual choice for what you seem to want to be doing is a
"linear-phase" or "Bessel filter", though a "synchronously tuned"
filter (consisting of identical multiple poles) actually gives fastest
settling for a given number of poles, with the step getting to better
than 99% after five time constants. Adding more poles makes the step
steeper at the 50% point, and pushes the 50% point back from around one
time constant at one pole to closer to three at ten poles.
A simple LCR filter is two poles ...
---------
Bill Sloman, Nijmegen
|
Do it digitally.
Distortionless digital filters are superb because they can look
backwards as well as forwards in time.
More on my website.
But if you must go analog, use my Active Filter Cookbook.
--
Many thanks,
Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com
Please visit my GURU's LAIR web site at http://www.tinaja.com |
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Tam/WB2TT
Guest
|
| Posted:
Fri Feb 11, 2005 10:22 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
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|
"Viram" <sorry@.no.spam> wrote in message
news:4c1688b723a5876fcffea18db84efe0f@localhost.talkaboutelectronicequipment.com...
| Quote: | I'm trying to design a LP-filter with a cut off at around 500 Hz. My
problem is getting a short response time and low/no resonance peak. What
order should the filter be? I'm currently trying with a simple
LC-filter...
Unless you like inductors the size of tuna cans, use an active filter. |
(Except if you are building a speaker crossover filter).
Tam |
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Guest
|
| Posted:
Fri Feb 11, 2005 11:40 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
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Don Lancaster wrote:
| Quote: | bill.sloman@ieee.org wrote:
Viram wrote:
I'm trying to design a LP-filter with a cut off at around 500 Hz.
My
problem is getting a short response time and low/no resonance peak.
What
order should the filter be? I'm currently trying with a simple
LC-filter...
You need to get hold of a decent text on filter design - I use the
"Electronic Filter Design Handbook" by Arthur B. Williams and Fred
J.
Taylor - ISBN 0-07-070434-1. Since then there has been a third
edition
(ISBN 0-07-070430-9) which is supposed to be even better, but it
seems
to be out of print - www.amazon.com offers three second hand copies
for
about $130. You should be able to find it - or something very like
it -
in a university library.
The usual choice for what you seem to want to be doing is a
"linear-phase" or "Bessel filter", though a "synchronously tuned"
filter (consisting of identical multiple poles) actually gives
fastest
settling for a given number of poles, with the step getting to
better
than 99% after five time constants. Adding more poles makes the
step
steeper at the 50% point, and pushes the 50% point back from around
one
time constant at one pole to closer to three at ten poles.
A simple LCR filter is two poles ...
---------
Bill Sloman, Nijmegen
Do it digitally.
Distortionless digital filters are superb because they can look
backwards as well as forwards in time.
More on my website.
But if you must go analog, use my Active Filter Cookbook.
Please visit my GURU's LAIR web site at http://www.tinaja.com
|
Don Lancaster's Active Filter Cookbook has many fans. Williams and
Taylor cover a wider range of filters and filter types.
-------
Bill Sloman, Nijmegen |
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| Back to top |
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Joel Kolstad
Guest
|
| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
|
|
"gwhite" <gwhite@deadend.com> wrote in message
news:420EABF3.37522B34@deadend.com...
Zverev is a great book, certainly, but it's really not a good 'introductory'
tome on the subject. I think the poster would be better off with Don
Lancaster's old book, or perhaps "Analog and Digital Filter Design" by
Winder.
Noble Publishing is also the home of Randy Rhea, whose book "HF Filter
Design and Computer Simulation" is quite good as well. Rhea's a very
practical kind of guy... (although if you look at the price of his
publications, he wants to make a pretty darned good living at it too!)
---Joel |
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gwhite
Guest
|
| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
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|
bill.sloman@ieee.org wrote:
| Quote: |
Don Lancaster wrote:
bill.sloman@ieee.org wrote:
Viram wrote:
I'm trying to design a LP-filter with a cut off at around 500 Hz.
My
problem is getting a short response time and low/no resonance peak.
What
order should the filter be? I'm currently trying with a simple
LC-filter...
You need to get hold of a decent text on filter design - I use the
"Electronic Filter Design Handbook" by Arthur B. Williams and Fred
J.
Taylor - ISBN 0-07-070434-1. Since then there has been a third
edition
(ISBN 0-07-070430-9) which is supposed to be even better, but it
seems
to be out of print - www.amazon.com offers three second hand copies
for
about $130. You should be able to find it - or something very like
it -
in a university library.
The usual choice for what you seem to want to be doing is a
"linear-phase" or "Bessel filter", though a "synchronously tuned"
filter (consisting of identical multiple poles) actually gives
fastest
settling for a given number of poles, with the step getting to
better
than 99% after five time constants. Adding more poles makes the
step
steeper at the 50% point, and pushes the 50% point back from around
one
time constant at one pole to closer to three at ten poles.
A simple LCR filter is two poles ...
---------
Bill Sloman, Nijmegen
Do it digitally.
Distortionless digital filters are superb because they can look
backwards as well as forwards in time.
More on my website.
But if you must go analog, use my Active Filter Cookbook.
Please visit my GURU's LAIR web site at http://www.tinaja.com
Don Lancaster's Active Filter Cookbook has many fans. Williams and
Taylor cover a wider range of filters and filter types.
|
If you want the bible of filters...:
http://www.amazon.com/exec/obidos/tg/detail/-/0471986801/
The time plots--which is what the OP cares about--are all there.
I don't have the following, but it too has focus on the time domain and is less
expensive:
http://www.noblepub.com/shopexd.asp?id=6
Don's book works great where the needs are straightfoward and the frequency is
not very high. It is a fast path to getting done, and that says something. |
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| Back to top |
|
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Guest
|
| Posted:
Sun Feb 13, 2005 5:00 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
|
|
gwhite wrote:
| Quote: | bill.sloman@ieee.org wrote:
Don Lancaster wrote:
bill.sloman@ieee.org wrote:
Viram wrote:
I'm trying to design a LP-filter with a cut off at around 500
Hz.
My
problem is getting a short response time and low/no resonance
peak.
What
order should the filter be? I'm currently trying with a simple
LC-filter...
You need to get hold of a decent text on filter design - I use
the
"Electronic Filter Design Handbook" by Arthur B. Williams and
Fred
J.
Taylor - ISBN 0-07-070434-1. Since then there has been a third
edition
(ISBN 0-07-070430-9) which is supposed to be even better, but
it
seems
to be out of print - www.amazon.com offers three second hand
copies
for
about $130. You should be able to find it - or something very
like
it -
in a university library.
The usual choice for what you seem to want to be doing is a
"linear-phase" or "Bessel filter", though a "synchronously
tuned"
filter (consisting of identical multiple poles) actually gives
fastest
settling for a given number of poles, with the step getting to
better
than 99% after five time constants. Adding more poles makes the
step
steeper at the 50% point, and pushes the 50% point back from
around
one
time constant at one pole to closer to three at ten poles.
A simple LCR filter is two poles ...
---------
Bill Sloman, Nijmegen
Do it digitally.
Distortionless digital filters are superb because they can look
backwards as well as forwards in time.
More on my website.
But if you must go analog, use my Active Filter Cookbook.
Please visit my GURU's LAIR web site at http://www.tinaja.com
Don Lancaster's Active Filter Cookbook has many fans. Williams and
Taylor cover a wider range of filters and filter types.
If you want the bible of filters...:
http://www.amazon.com/exec/obidos/tg/detail/-/0471986801/
The time plots--which is what the OP cares about--are all there.
|
Williams and Taylor cite Zverev very frequently, and include time plots
for every filter type - both step response and impulse response. I
imagine that Zverev presents the theory better - Williams and Taylor
just direct you to the relevant bit of the literature - but Williams
and Taylor is very much a book for working enegineers.
| Quote: | I don't have the following, but it too has focus on the time domain
and is less
expensive:
http://www.noblepub.com/shopexd.asp?id=6
Don's book works great where the needs are straightfoward and the
frequency is
not very high. It is a fast path to getting done, and that says
something. |
Williams and Taylor is handy when the situation gets more complicated -
I once ran into a situation where we needed a fast-settling filter, but
couldn't start the filter chain with a high-Q stage because of the risk
of clipping, and was able to find a "linear phase with equiripple
error" filter which did the job.
The electron microscope involved ended up being loaded on the truck at
eleven in the evening under the eye of the managing director, so I
scored a few brownie points on that one.
-------
Bill Sloman, Nijmegen |
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Rob Gaddi
Guest
|
| Posted:
Mon Feb 14, 2005 10:57 pm Post subject:
Re: Low pass filter, cut off 500 Hz, short response time... |
|
|
Tam/WB2TT wrote:
| Quote: | "Viram" <sorry@.no.spam> wrote in message
news:4c1688b723a5876fcffea18db84efe0f@localhost.talkaboutelectronicequipment.com...
I'm trying to design a LP-filter with a cut off at around 500 Hz. My
problem is getting a short response time and low/no resonance peak. What
order should the filter be? I'm currently trying with a simple
LC-filter...
Unless you like inductors the size of tuna cans, use an active filter.
(Except if you are building a speaker crossover filter).
Tam
I'll second that one. If you head over to TI's site and check their |
analog knowledge base for a program called FilterPro it'll design RC
active filters for you up to 10 poles with either MFB or Sallen-Key
topologies. Though in my opinion they're far too conservative on the
gain-bandwith requirements of the op-amps. |
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