regarding filters in vhdl

V

viswanath

Guest
Hi,
I have to design a low pass filter in VHDL. How can one go about
designing such a filter when the medium is event driven and time
domain based??
How should one decide on the filter characteristics if we just know
the symbol time rate.
If I am using standard VHDL and not AMS is it possible for me to
design such a filter which is used in the recovery loops of receiver?
Most of the references on filter and digital communications refer to
frequency domain analysis. How can I go around this problem?
If the input is a pulse then a low pass filter is an integrate and
dump. However if I have a sampled sine wave how could I design a low
pass filter? Could you please reply and let me know?
I would grealty appreciate your reply.
Looking forward to your replies,
Thanks
Viswanath
PS: I would be needing a filter after the mixing of two sine waves to
filter out the higher frequency components.
 
Your kidding, right?
Think shift register..
Thing sample rate..
Think FIR..
Think

"viswanath" <daita@eng.usf.edu> wrote in message
news:791e9679.0405171227.5608952@posting.google.com...
Hi,
I have to design a low pass filter in VHDL. How can one go about
designing such a filter when the medium is event driven and time
domain based??
How should one decide on the filter characteristics if we just know
the symbol time rate.
If I am using standard VHDL and not AMS is it possible for me to
design such a filter which is used in the recovery loops of receiver?
Most of the references on filter and digital communications refer to
frequency domain analysis. How can I go around this problem?
If the input is a pulse then a low pass filter is an integrate and
dump. However if I have a sampled sine wave how could I design a low
pass filter? Could you please reply and let me know?
I would grealty appreciate your reply.
Looking forward to your replies,
Thanks
Viswanath
PS: I would be needing a filter after the mixing of two sine waves to
filter out the higher frequency components.
Click to expand...
 
You could use a moving average to implement a low pass filter...

Create a circular buffer and place the input data "on the fly" into the
register pointed to by a resetable counter.
The more registers in the circular buffer, the lower the filter frequency
with the effect of more smoothing of the
data.

I would make a little RAM internally for the circular buffer...

Don Golding

"fabbl" <nospam@nospam.com> wrote in message
news:YRcqc.2300$dF.763@newssvr32.news.prodigy.com...
Your kidding, right?
Think shift register..
Thing sample rate..
Think FIR..
Think

"viswanath" <daita@eng.usf.edu> wrote in message
news:791e9679.0405171227.5608952@posting.google.com...
Hi,
I have to design a low pass filter in VHDL. How can one go about
designing such a filter when the medium is event driven and time
domain based??
How should one decide on the filter characteristics if we just know
the symbol time rate.
If I am using standard VHDL and not AMS is it possible for me to
design such a filter which is used in the recovery loops of receiver?
Most of the references on filter and digital communications refer to
frequency domain analysis. How can I go around this problem?
If the input is a pulse then a low pass filter is an integrate and
dump. However if I have a sampled sine wave how could I design a low
pass filter? Could you please reply and let me know?
I would grealty appreciate your reply.
Looking forward to your replies,
Thanks
Viswanath
PS: I would be needing a filter after the mixing of two sine waves to
filter out the higher frequency components.
Click to expand...
 
viswanath wrote:


I have to design a low pass filter in VHDL. How can one go about
designing such a filter when the medium is event driven and time
domain based??
Click to expand...
Remember, that Fourier Transform is closely related to Laplace Transform
and Z Transform.

For conversion from s-space (Laplace) to z-space (sampled data) use
bilinear transform.

In z-space filter coefficients are the same as the coefficients of
polynomials. Therefore just pick a polynomial, that provides your
desired frequence response (Butterworth, Chebychev...) and compute the
polynomial coefficients.
Maybe "Passive & Active Filters: Theory & Implementations" by Wai-Kai
Chen ( http://www.mathematicsbooks.org/047182352X.html ) or any other
book about digital filter design may be helpful.



Ralf
 
Hello,

For generation of digital filters, you can use ONEoverT with it's VHDL
module. It will produce easily readable,
well commented RTL vhdl which you can then keep and add to your VHDL
library.
www.tyder.com

Best Regards
Michael
"viswanath" <daita@eng.usf.edu> wrote in message
news:791e9679.0405171227.5608952@posting.google.com...
Hi,
I have to design a low pass filter in VHDL. How can one go about
designing such a filter when the medium is event driven and time
domain based??
How should one decide on the filter characteristics if we just know
the symbol time rate.
If I am using standard VHDL and not AMS is it possible for me to
design such a filter which is used in the recovery loops of receiver?
Most of the references on filter and digital communications refer to
frequency domain analysis. How can I go around this problem?
If the input is a pulse then a low pass filter is an integrate and
dump. However if I have a sampled sine wave how could I design a low
pass filter? Could you please reply and let me know?
I would grealty appreciate your reply.
Looking forward to your replies,
Thanks
Viswanath
PS: I would be needing a filter after the mixing of two sine waves to
filter out the higher frequency components.
Click to expand...
 
Whoa, back up! You should not be using VHDL to design the filter; it
should be used to implement the filter you have designed using more
appropriate tools. There are many filter design applications (matlab has
one, there is also low cost FIR filter package called ScopeFIR available
through DSP_guru.com). Use that to determine an appropriate filter
structure and coefficients, then use the VHDL or a generator such as the
xilinx core generator to generate the filter logic to implement that
filter. It sounds like you need to gather a bit more background in DSP
before delving into the nuts and bolts of the design.

Others have mentioned a moving average for low pass filtering. Such a
filter is not a very good low pass filter, it's frequency response is
sin(x)/x. It is fine for crude low pass, or as a pre-filter in a
multi-rate filter chain, but not very good as the only filter.

viswanath wrote:

Hi,
I have to design a low pass filter in VHDL. How can one go about
designing such a filter when the medium is event driven and time
domain based??
How should one decide on the filter characteristics if we just know
the symbol time rate.
If I am using standard VHDL and not AMS is it possible for me to
design such a filter which is used in the recovery loops of receiver?
Most of the references on filter and digital communications refer to
frequency domain analysis. How can I go around this problem?
If the input is a pulse then a low pass filter is an integrate and
dump. However if I have a sampled sine wave how could I design a low
pass filter? Could you please reply and let me know?
I would grealty appreciate your reply.
Looking forward to your replies,
Thanks
Viswanath
PS: I would be needing a filter after the mixing of two sine waves to
filter out the higher frequency components.
Click to expand...
--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email ray@andraka.com
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top