[SI-LIST] Re: characteristic impedance at DC
- From: mohammad haaeri <haaeri@xxxxxxxxx>
- To: "Oh, Dan" <doh@xxxxxxxxxx>
- Date: Tue, 10 Apr 2012 08:07:43 -0700
Hi Dan,
I agree about considering loss at DC and calculating it correctly for DC to
have a good time-domain simulation.
I don't agree with what you calculated for characteristic impedance going
to 0.
Thanks,
mohammad
On Mon, Apr 9, 2012 at 9:27 PM, Oh, Dan <doh@xxxxxxxxxx> wrote:
> Hi Mohammad,
>
> My name is Dan Oh and I am one of the coauthors of that paper.
> Yes, you have correctly pointed out that we did not consider the TDR cable
> frequency dependence nor its loss. However, I believe it's contribution
> should be minimal.
> I just wanted to clarify why the loss frequency value is very important as
> we pointed out in our paper. The low frequency eventually dictates the
> static-state behavior. Although it does not affect the transient region
> which contains lots dynamics, the static value is very important for
> digital signals. I guess you would understand this since you read our paper.
> Like Howard mentioned in the later email, if you have set G to be zero,
> you will see RC line behavior which reaches to the static value extremely
> slowly. You can try this using HSPICE with realistic PCB trace models which
> typically have very small G values at low frequency. In most PCB or package
> traces, this type of behavior does not make sense as measurements show
> otherwise. We used TDR measurement to fix this issue and shows good
> correlation. This demonstrates that TDR loss or frequency dependence were
> very small.
> There are several other papers which talks about low frequency modeling
> issues besides our paper. They all demonstrate severe issues. I can forward
> a few references. If you would like to discuss further, please send me a
> separate email. I am very interested to discuss this over with you. FYI, I
> have been developing a RLGC solver and transmission line models for many
> years :).
> Best,
>
> -Dan Oh
>
> ___________________________________________
> Dan (KyungSuk) Oh, Ph.D.
> Technical Director of Signal and Power Integrity
> Rambus Inc.
> (B) 408-462-8363
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of mohammad haaeri
> Sent: Monday, April 09, 2012 5:34 PM
> To: shlepnev@xxxxxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: characteristic impedance at DC
>
> Thanks Yuriy for your response, it makes sense.
> I think what's been calculated for characteristic impedance at low
> frequencies in "Implementation of Broadband transmission line models with
> accurate low-frequency response for high speed system simulations" in
> DesignCon 2006 is not correct (although it has improved the time domain
> simulation results!). They are assuming only the transmission line under
> test is frequency dependent and calculate its limit going to low
> frequencies not the TDR cable (which is another transmission line and it
> doesn't have 50ohms going to zero). (page 11, equation (5)). That's the
> reason they are coming up with a characteristic of 25.7ohms at DC for a
> transmission line!
>
>
>
>
>
> On Mon, Apr 9, 2012 at 5:15 PM, Yuriy Shlepnev <shlepnev@xxxxxxxxxxxxx
> >wrote:
>
> > Mohammad,
> >
> > See my answers below.
> >
> > Best regards,
> > Yuriy
> >
> > Yuriy Shlepnev, Ph.D.
> > President, Simberian Inc.
> > 3030 S Torrey Pines Dr. Las Vegas, NV 89146, USA Office
> > +1-702-876-2882 Cell +1-206-409-2368
> > Skype: shlepnev
> > www.simberian.com
> >
> >
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On
> > Behalf Of mohammad haaeri
> > Sent: Monday, April 09, 2012 3:31 PM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] characteristic impedance at DC
> >
> > Hi,
> > What is the characteristic impedance of a transmission line at DC? If
> > you are saying Z0=sqrt(Rdc/Gdc) at DC, since Gdc=0, and Rdc is not
> > zero, therefore Z0 is infinite. Is it correct?
> > YS: Yes, this is correct for a lossy line that does not have
> > conductive losses in the admittance per unit length (technically in
> dielectric).
> > Though, there is no waves at DC, for TEM mode we can calculate
> > asymptotes of the impedance and admittance per unit length and the
> > characteristic impedance at DC.
> >
> > How does behavior of L, R, G, and C (line parameters) change vs.
> > frequency (at low and DC, and at very high frequency)?
> > YS: It obviously depends on a transmission line type. See analysis for
> > a microstrip line in this app note
> > http://www.simberian.com/AppNotes/MicrostripImpedanceAndTDR_2009_04.pd
> > f Impedance grows at lower frequencies if dielectric model has only
> > polarization losses. In reality, there are some conductive losses in
> > dielectric and thus the asymptote of the characteristic impedance ad
> > DC is not infinity. As someone already noted, the low-frequency growth
> > of the impedance has small impact on overall behavior of the line. It
> > should also not be confused with the conductor resistance that is more
> > important to account at DC. For a microstrip line, the impedance also
> > grows at very high frequencies.
> >
> > Can Z0=sqrt(R+jwl/G+jwc) be used for all frequencies?
> > YS: Yes, as long as the impedance (R+jwL) and admittance (G+iwC) per
> > unit length are appropriately defined. The formula does not have
> > limitations neither at low nor at high frequencies, though this is
> > relatively complicated subject for a short posting.
> >
> > Thanks,
> > mohammad
> >
> >
> > ------------------------------------------------------------------
> > 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 forum is accessible at:
> > http://tech.groups.yahoo.com/group/si-list
> >
> > 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 forum is accessible at:
> http://tech.groups.yahoo.com/group/si-list
>
> 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 forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
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
Other related posts:
