Hai, Is there any formula or general rule to set output width of FIR filter given its input ,coefficients width and number of taps.?? I red in some data sheet of FIR filter deisgn as: output width = input width+coefficient width+logN(base 2) In some other data sheet of FIR filter deisgn as: output width = 2*input width+logN(base 2) which of the above is correct??pls give some link for refernce doc explaining the general rule to set o/p width.. regards, faz
FIR filter O/p width
Started by ●May 27, 2008
Reply by ●May 27, 20082008-05-27
>Is there any formula or general rule to set output width of FIR filter >given its input ,coefficients width and number of taps.??There is no such Formula.>I red in some data sheet of FIR filter deisgn as: >output width = input width+coefficient width+logN(base 2) > >In some other data sheet of FIR filter deisgn as: >output width = 2*input width+logN(base 2)Both the formula are incorrect and most probably u would have read them in some FPGA white paper.
Reply by ●May 27, 20082008-05-27
On May 27, 5:39�pm, "bharat pathak" <bha...@arithos.com> wrote:> >Is there any formula or general rule to set output width of FIR filter > >given its input ,coefficients width and number of taps.?? > > There is no such Formula. > > >I red in some data sheet of FIR filter deisgn as: > >output width = input width+coefficient width+logN(base 2) > > >In some other data sheet �of FIR filter deisgn as: > >output width = 2*input width+logN(base 2) > > Both the formula are incorrect and most probably u would > have read them in some FPGA white paper.Hai, U cannot say it as incorrect because they are following some practical consideration as given below.. http://personal.rdu.bellsouth.net/~yatesc/fir.pdf pls go through the fixed point summation theorem in page 6.. All FPGA vendors like ALTERA,XILINX,ACTEL,ALDEC,LATTICE follow this formula for their FIR filter design generation...so how it can be incorrect... Still u are not convinced...then justify why it is wrong??and explain wat is the right way to calculate it?? regards, faz
Reply by ●May 27, 20082008-05-27
faz <fazulu.vlsi@gmail.com> writes:> On May 27, 5:39�pm, "bharat pathak" <bha...@arithos.com> wrote: >> >Is there any formula or general rule to set output width of FIR filter >> >given its input ,coefficients width and number of taps.?? >> >> There is no such Formula. >> >> >I red in some data sheet of FIR filter deisgn as: >> >output width = input width+coefficient width+logN(base 2) >> >> >In some other data sheet �of FIR filter deisgn as: >> >output width = 2*input width+logN(base 2) >> >> Both the formula are incorrect and most probably u would >> have read them in some FPGA white paper. > > Hai, > > U cannot say it as incorrect because they are following some practical > consideration as given below.. > > http://personal.rdu.bellsouth.net/~yatesc/fir.pdfHi Faz, I can't believe that link still works! I haven't had my internet service with Bellsouth for at least 3 years! (And that is an old version of the paper.) Please use the following link instead: http://www.digitalsignallabs.com/fir.pdf http://www.digitalsignallabs.com/fp.pdf> Still u are not convinced...then justify why it is wrong??and explain > wat is the right way to calculate it??Faz, Bharat, if I have made an error, please let me know. I will be watching this thread. -- % Randy Yates % "Bird, on the wing, %% Fuquay-Varina, NC % goes floating by %%% 919-577-9882 % but there's a teardrop in his eye..." %%%% <yates@ieee.org> % 'One Summer Dream', *Face The Music*, ELO http://www.digitalsignallabs.com
Reply by ●May 27, 20082008-05-27
Randy,
The output wordlength is briefly touched upon in fir.pdf
equations 86 and 87. It just talks about one part of the story,
and that part is overflow, which you have mentioned in your doc.
And maybe this is the reason why you are closely following the
discussion.
I will be sending you a mail shortly with all the details and
equations. Please hold on for sometime, as I am in middle of
some other time critical work.
Regards
Bharat
The World Is Flat: A Brief History of the Twenty-First Century
Reply by ●May 27, 20082008-05-27
On May 27, 7:10�pm, Randy Yates <ya...@ieee.org> wrote:> faz <fazulu.v...@gmail.com> writes: > > On May 27, 5:39�pm, "bharat pathak" <bha...@arithos.com> wrote: > >> >Is there any formula or general rule to set output width of FIR filter > >> >given its input ,coefficients width and number of taps.?? > > >> There is no such Formula. > > >> >I red in some data sheet of FIR filter deisgn as: > >> >output width = input width+coefficient width+logN(base 2) > > >> >In some other data sheet �of FIR filter deisgn as: > >> >output width = 2*input width+logN(base 2) > > >> Both the formula are incorrect and most probably u would > >> have read them in some FPGA white paper. > > > Hai, > > > U cannot say it as incorrect because they are following some practical > > consideration as given below.. > > >http://personal.rdu.bellsouth.net/~yatesc/fir.pdf > > Hi Faz, > > I can't believe that link still works! I haven't had my internet > service with Bellsouth for at least 3 years! (And that is an > old version of the paper.) > > Please use the following link instead: > > �http://www.digitalsignallabs.com/fir.pdf > �http://www.digitalsignallabs.com/fp.pdf > > > Still u are not convinced...then justify why it is wrong??and explain > > wat is the right way to calculate it?? > > Faz, Bharat, if I have made an error, please let me know. I will > be watching this thread. > -- > % �Randy Yates � � � � � � � � �% "Bird, on the wing, > %% Fuquay-Varina, NC � � � � � �% � goes floating by > %%% 919-577-9882 � � � � � � � �% � but there's a teardrop in his eye..." > %%%% <ya...@ieee.org> � � � � � % 'One Summer Dream', *Face The Music*, ELOhttp://www.digitalsignallabs.comhai, Your document describe consideration for fixed point number but for floating point number whether same condition M+N+log2(N) can be used?? regards, faz
Reply by ●May 27, 20082008-05-27
"bharat pathak" <bharat@arithos.com> writes:> Randy, > > The output wordlength is briefly touched upon in fir.pdf > equations 86 and 87. It just talks about one part of the story, > and that part is overflow, which you have mentioned in your doc.Well, I mention maintaining precision and avoiding overflow. In other words, there are at least two "parts of the story" there. Maybe you have more parts? -- % Randy Yates % "The dreamer, the unwoken fool - %% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..." %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Eldorado Overture', *Eldorado*, ELO http://www.digitalsignallabs.com
Reply by ●May 27, 20082008-05-27
Randy Yates wrote:> "bharat pathak" <bharat@arithos.com> writes: > >> Randy, >> >> The output wordlength is briefly touched upon in fir.pdf >> equations 86 and 87. It just talks about one part of the story, >> and that part is overflow, which you have mentioned in your doc. > > Well, I mention maintaining precision and avoiding overflow. In other > words, there are at least two "parts of the story" there. Maybe you have > more parts?How about the number of worthwhile (significant) bits? When I measure the diameter of a tree as 2 inches, it's naive to cite it's circumference as 6.283185307179586476925286766559 inches. For this kind of measurement, fractional Angstrom units don't mean much. When later truncation creates so little noise that the noise from the original quantization masks it, any more bits are simply wasted. jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 27, 20082008-05-27
Jerry Avins <jya@ieee.org> writes:> Randy Yates wrote: >> "bharat pathak" <bharat@arithos.com> writes: >> >>> Randy, >>> >>> The output wordlength is briefly touched upon in fir.pdf >>> equations 86 and 87. It just talks about one part of the story, >>> and that part is overflow, which you have mentioned in your doc. >> >> Well, I mention maintaining precision and avoiding overflow. In other >> words, there are at least two "parts of the story" there. Maybe you have >> more parts? > > How about the number of worthwhile (significant) bits? When I measure > the diameter of a tree as 2 inches, it's naive to cite it's > circumference as 6.283185307179586476925286766559 inches. For this > kind of measurement, fractional Angstrom units don't mean much. > > When later truncation creates so little noise that the noise from the > original quantization masks it, any more bits are simply wasted.If you can make some statistical assumptions about the input data, then perhaps you can get away with fewer bits. But of course in general, using any fewer bits would lose information. -- % Randy Yates % "Remember the good old 1980's, when %% Fuquay-Varina, NC % things were so uncomplicated?" %%% 919-577-9882 % 'Ticket To The Moon' %%%% <yates@ieee.org> % *Time*, Electric Light Orchestra http://www.digitalsignallabs.com
Reply by ●May 27, 20082008-05-27
Randy Yates wrote:> Jerry Avins <jya@ieee.org> writes: > >> Randy Yates wrote: >>> "bharat pathak" <bharat@arithos.com> writes: >>> >>>> Randy, >>>> >>>> The output wordlength is briefly touched upon in fir.pdf >>>> equations 86 and 87. It just talks about one part of the story, >>>> and that part is overflow, which you have mentioned in your doc. >>> Well, I mention maintaining precision and avoiding overflow. In other >>> words, there are at least two "parts of the story" there. Maybe you have >>> more parts? >> How about the number of worthwhile (significant) bits? When I measure >> the diameter of a tree as 2 inches, it's naive to cite it's >> circumference as 6.283185307179586476925286766559 inches. For this >> kind of measurement, fractional Angstrom units don't mean much. >> >> When later truncation creates so little noise that the noise from the >> original quantization masks it, any more bits are simply wasted. > > If you can make some statistical assumptions about the input data, then > perhaps you can get away with fewer bits. But of course in general, > using any fewer bits would lose information.It would lose something, but would what is lost be information? Would truncating the tree diameter from 6.283185307179586476925286766559 to 6.283, thus reporting it to the nearest thousandth of an inch, (or 25 microns) lose information? What is the meaning of 6.2831853071795864 +/- .001? It's like giving baking time to milliseconds when the oven temperature is known only within a few degrees. DSP is about numbers, and numbers can have any presumed precision. When those numbers are used to describe something, there is a limit to how precise the description can meaningfully be. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
