[SI-LIST] Re: inductance of differential stripline
- From: "Mark Burford" <Mark_Burford@xxxxxxxxxxx>
- To: <weirsi@xxxxxxxxxx>
- Date: Tue, 8 Feb 2005 10:42:25 -0000
Dear Sirs, Many thanks for your input.
I can say that I tried the link supplied by Joe and found there to be a
significant difference in the results of the link's calculator and my
equations obtained from various sources. Lists below are the equation
set I am using and where I obtained them from, comments welcome.
National Semiconductor's LVDS guide
z0_single =3D (60.0/SQRT(Er))*log((1.9*b)/((0.8*width_ic)+height_ic));
z0_diff =3D 2.0*Z0_nat*(1.0-0.748*exp(-2.9*(line_sep/h1)));=20
delay_of_line =3D 1.0/(C/SQRT(Er)); --secs/m
l_line =3D delay_line*Z0_diff;
l_mut =3D l_line*(1.0/(1.0+(line_sep/h1)^2)); --sigcon.com
I noted that the link supplied by Joe did not take account of Er however
this has no effect on the inductance as it is a factor of both impedance
and delay of the line and the effects cancel. The link uses this for
coplanar traces, there is no mention of a ground plane between which my
traces are sitting, would this affect the inductance by increasing or
decreasing it? Depends on distance to gnd plans I suppose? The
equation above accounts for dist to gnd plane (h1)
Many thanks
Mark
Southampton
UK
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Steve Weir
Sent: 08 February 2005 07:35
To: joepaulm@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: inductance of differential stripline
That is correct it is lower than 2X. Istvan only offered the
description=20
as an approximation to help with Mark's intuitive understanding.
Steve
At 12:12 PM 2/8/2005 +0550, Joe Paul wrote:
>Sir,
>
>Excuse me and Correct me if I am wrong
>
>I feel that the inductance of the differential line measured by
applying a=20
>differential signal on a
>pair of differential traces, will be less than the twice the inductance
>measured by applying a
>single ended signal on a trace , as the magnetic field formed due to=20
>current in one traces aiding
>the current flow other.
>
>i.e differential inductance will be, equlaent to 2 single ended=20
>inductances in series and their
>mutual inductance between them in parallel.
>
>I don't know about the accuracy the tool Iused , but Inductance
calculated=20
>shows that the mutual
>inductance are not that small to be ignored.
>(as per Inductance calculator at http://emcsun.ece.umr.edu/new-induct/
)
>
>My assumptions are
>* Single ended inductance measured with no other lines in its vicinity.
>* Differential inductance measured with no other lines other than
them.
>
>
>
>Joe
>Ordyn,India.
>
> > Mark,
> >
> > Welome to the si-list forum.
> >
> > In a very simplistic way we can say that the differential impedance
> > is twice the single-ended impedance because we connect two
> > transmission lines in series. Series impedances add, similarly
> > series-connected inductances add. You can use the same
> > formula of Zo*delay, just have to substitute the correct terms:
> > differential impedance and differential (odd-mode) delay.
> > You can find very good tutorials on the subject on the TDA
> > Systems website. http://www.tdasystems.com/
> >
> > Regards,
> >
> > Istvan Novak
> > SUN Microsystems
> >
> > Mark Burford wrote:
> >
> > >Hi guys, just subscribed.
> > >I understand the inductance of stripline to be Z0*delay_of_line
> > >Could anyone tell me what the inductance is for differential odd
mode
> > >stripline please? Does it change? I know Z0 for differential
stripline
> > >is near double that of single stripline, but does this affect
> > >inductance?
> > >
> > >Many thanks
> > >
> > >Mark Burford
> > >Mburford AT xyratex DOT com
> > >
> > >
> > >
> > >
> >
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