Yes. In fact, I was really just paraphrasing what Howard Johnson and Martin Graham relate in Appendix B of their book, "High-Speed Digital Design - A Handbook of Black Magic" (Prentice Hall, New Jersey, 1993). Sorry, Drs., I should have given you credit originally. -db > -----Original Message----- > From: Asbenson, Lyndell L [mailto:lyndell.l.asbenson@xxxxxxxxx] > Sent: Monday, May 07, 2007 5:41 PM > To: David Banas > Subject: RE: [SI-LIST] Re: Rise time bandwidth relation >=20 > WOW, Is there any book that describes this? Thanks Lyndell >=20 > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of David Banas > Sent: Monday, May 07, 2007 3:25 PM > To: rohitsharma@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Rise time bandwidth relation >=20 > If you start with the assumption that your observed edge is the result > of an ideal edge having moved through some composite channel with a > Gaussian shaped impulse response, g(t), with "-3dB" bandwidth, B, then > your observed edge, s(t), will be the integral of that impulse response: >=20 > s(t) =3D3D Integral{g(t) dt} (1) >=20 > If: >=20 > G(w) =3D3D exp{-(a * w)^2} (2) >=20 > Then: >=20 > g(t) =3D3D exp{-(t/2a)^2} / 2*sqrt{pi * a} (3) >=20 > B is found by setting G(w) =3D3D 0.707. We get: >=20 > B =3D3D .0937 / a. (4) >=20 > The "error function" (ERF() in Excel) is defined as: >=20 > ERF(z) =3D3D (2/sqrt(pi)) * Integral_0-z{exp(-u^2) du} (5) >=20 > and gives the area under the Gaussian curve from -z to +z, normalized to > 1. (That is, ERF(Infinity) =3D3D 1.) ERF() can be used to find the =3D > integral > of g(t) by substituting "t/2a" from (3) in for "u" in (5). The "10-90%" > rise time of s(t) can be found by setting ERF(z) =3D3D 80%, solving = for =3D > "u", > and then setting: >=20 > risetime/2a =3D3D 2u (6) >=20 > (This works because g(t) is symmetric about its peak, and the 20% of its > area that we're leaving out of the integral is precisely divided in > half: 10% before the integrated portion and 10% after, yielding the 10% > and 90% points in s(t), respectively. We have to double "u", due to the > way ERF() is defined. (i.e. - ERF(z) integrates over the range > [-z,+z].)) We get: >=20 > u =3D3D 0.9 (7) >=20 > rise-time =3D3D 2u * 2a =3D3D 3.6 * a (8) >=20 > and, using (4), >=20 > rise-time =3D3D 0.337 / B (9) >=20 > -db >=20 > > -----Original Message----- > > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx] > > On Behalf Of Rohit Sharma > > Sent: Monday, May 07, 2007 8:01 AM > > To: si-list@xxxxxxxxxxxxx > > Subject: [SI-LIST] Re: Rise time bandwidth relation > >=3D20 > > Hi All, > > Can somebody help me in understanding the derivation of the > following > > formula for digital signals:- > > Bandwidth =3D3D 0.35/Rise time. > >=3D20 > > Regards, > > Rohit > >=3D20 > >=3D20 > >=3D20 > > -- > >=3D20 > > Message Classification :- > > [ ] Public > > [x] Freescale Internal Use Only > > [ ] Freescale Confidential Proprietary > >=3D20 > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >=3D20 > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > >=3D20 > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >=3D20 > >=3D20 > > List technical documents are available at: > > http://www.si-list.net > >=3D20 > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > >=3D20 > >=3D20 >=20 >=20 > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field >=20 > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list >=20 > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field >=20 >=20 > List technical documents are available at: > http://www.si-list.net >=20 > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu >=20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu