[SI-LIST] Re: Power planes
- From: "Tabatchnick, Justin" <justin.tabatchnick@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 24 Jul 2003 10:06:59 -0700
Ray;
Since the effective dielectric constant is a function of the reference
ground plane distance and the trace width, ground plane distance does
effect velocity.
Justin
Intel , Sacramento
-----Original Message-----
From: Ray Anderson [mailto:Raymond.Anderson@xxxxxxx]=20
Sent: Thursday, July 24, 2003 9:28 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Power planes
>
>This is quite a general question.
>
>---------------------------------------------
>
>If I place the GND plane too close to the track wouldn't it affect the
velocity=20
of signal on track ?
>
>Possible reason is the capacitance b/w track and GND will increase
which will=20
cause the delay in changing signal(rising edges) as it will need more
time to=20
charge the increased capacitor value.Geoff just told us that placement
of GND=20
affects the velocity of Microstrip and Not Strip Line. How far is it
true ?
>
>=20
The distance between a signal trace and a reference plane in a
stack-up does not effect the velocity of the signal propagating=20
on the signal trace. It can effect the impedance of the signal
trace. The velocity of propagation is dependent only on the effective
dielectric constant (Er) or electric permittivity of the substrate
material.
=09
=09
Yes, there will be more distributed capacitance between the signal
trace and the plane for small spacings, but this does not effect
the velocity of propagation as the PUL inductance of the signal
trace will decrease as well.
some relevant equations:
------------------------
=09
Velocity =3D C/sqrt(Er) <=3D velocity is a function of Er
(where C is speed of light in this equation)
=09
Velocity =3D 11.8/sqrt(Er) inches/nSec <=3D numeric version of
above
=09
Velocity =3D 1/sqrt(L*C) hence:
L =3D (delay^2)/C and C =3D (delay^2)/L
=20
=20
=09
-Ray Anderson
Sun Microsystems
------------------------------------------------------------------
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 archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages=20
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 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
Other related posts:
