Hi Weston, Yes, this is a rather roundabout method to model a step function. My preference is to avoid using the UIC function. ------------------------------------------------ Tracy Barclay CAE Synopsys, Inc. -----Original Message----- From: Beal, Weston [mailto:Weston_Beal@xxxxxxxxxx] Sent: Friday, September 02, 2011 09:04 To: Tracy Barclay; David Banas Cc: 'si-list@xxxxxxxxxxxxx' Subject: RE: Impulse vs. Step Response? The step function is created in a roundabout fashion using the initial condition. The initial voltage on node -out- is set to 0V. Once the transient simulation starts, the voltage is allowed to rise up to its defined level of 1V. This method is defined by the .IC statement together with the UIC parameter on the .TRAN line. Weston -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Tracy Barclay Sent: Friday, September 02, 2011 8:00 AM To: David Banas Cc: 'si-list@xxxxxxxxxxxxx' Subject: [SI-LIST] Re: Impulse vs. Step Response? Hi David, For your transient analysis, I do not see a transient waveform defined in your netlist. The source Vin only defines a DC voltage and a AC voltage. I would expect to see something like: Vin in 0 DC 1 AC 1 PWL(0 1 0.05n 1 0.06n 0) Where the PWL definition defines the desired unit step. ------------------------------------------------ Tracy Barclay CAE Synopsys, Inc. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of David Banas Sent: Thursday, September 01, 2011 17:40 To: 'si-list@xxxxxxxxxxxxx' Subject: [SI-LIST] Impulse vs. Step Response? 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 ------------------------------------------------------------------ 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 ------------------------------------------------------------------ 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