"You are not driving your transient with a step" Why do you say that? -db -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir Sent: Thursday, September 01, 2011 6:40 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Impulse vs. Step Response? As long as the frequency / time domain conversions cover a wide enough frequency range the FD response and the FFT of the unit impulse should match. You are not driving your transient with a step so there should not be a need to consider U(w) = H(w)/jw Steve. On 9/1/2011 5:40 PM, David Banas wrote: > Hi all, > > I've got a puzzler. I'm using this HSpice deck: > > .TITLE AC Sweep vs. Transient Correlation > > .OPTION > + POST > + PROBE > + RUNLVL = 5 > > Rin in out r=1K > Cout out 0 c=1pF > Rout out 0 10MEG > > Vin in 0 DC 1 AC 1 > > .IC V(out) = 0 > > .AC DEC 10 1 1G > .TRAN 0.05n 1u 0 0.05n UIC > > .PROBE AC V(in) V(out) > .PROBE TRAN V(in) V(out) > > .END > > to get both the transfer function, H(w), (.AC command) and the unit step > response, u(t), (.TRAN command) of a simple RC LPF. > > Then, I take the FFT of the .TRAN output and compare it to the .AC output. > And they match! > > I wasn't expecting a match, since all my textbooks say there's a `jw' factor > relating the impulse response and the step response. That is: > > U(w) = H(w)/jw > > So, when I compared the 2 spectra, I was expecting the FFT of my .TRAN output > to have an extra 6dB/octave roll-off, as compared to the .AC output, due to > the `w' in the denominator, above. > > Can anyone shed some light on this? > > Thanks, > > David Banas > Sr. Member Technical Staff > Altera > +1-408-544-7667 - desk > > Did you know Altera offers over 150 free online technical training courses? > Take one today! > > > Confidentiality Notice. > This message may contain information that is confidential or otherwise > protected from disclosure. If you are not the intended recipient, you are > hereby notified that any use, disclosure, dissemination, distribution, or > copying of this message, or any attachments, is strictly prohibited. If you > have received this message in error, please advise the sender by reply > e-mail, and delete the message and any attachments. Thank you. > > ------------------------------------------------------------------ > 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 > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > -- Steve Weir IPBLOX, LLC 150 N. Center St. #211 Reno, NV 89501 www.ipblox.com (775) 299-4236 Business (866) 675-4630 Toll-free (707) 780-1951 Fax ------------------------------------------------------------------ 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 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu Confidentiality Notice. This message may contain information that is confidential or otherwise protected from disclosure. If you are not the intended recipient, you are hereby notified that any use, disclosure, dissemination, distribution, or copying of this message, or any attachments, is strictly prohibited. If you have received this message in error, please advise the sender by reply e-mail, and delete the message and any attachments. Thank you. ------------------------------------------------------------------ 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 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu