[SI-LIST] Re: Finding Er (Permitivity)
- From: V S <for_si2003@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 18 Jul 2003 15:08:09 -0700 (PDT)
Seems like , my earlier message was messed up , so
resending
Venu does not have any board detail.
If you have a high frequency Scope we can calculate
the Er as follows. Find a visible PCB track on the top
layer ( call it microstrip ). Feed a fast rising edge
on one end of it and observe the rising edge at the
two end of known length ( L) of the microstrip. Find
the skew between the two signal.
the propogation delay in ps of microstrip is roughly
t = L * 85 * sqrt ( 0.475 * Er +0.67 ) ps , L is in
inch
For example, if L = 4 inch
skew t = 570 ps
Then , Er = [ ( t/ 85*L)^2 - 0.67 ] / 0.475
= 4.3
TDR can also be used.
Thanks
Vikas Shukla
jeff_latourrette@xxxxxxxxxxx wrote:
Venu:
One other tiny issue with microstrip is that in
addition to frequency dependence, the effective
dielectric constant is also very geometry dependent,
on width and to a smaller extent the thickness:
epsilon(eff) = (epsilon(r)+1)/2 +
[(epsilon(r)-1)/2]*f(W/h) -
[(epsilon(r)-1)/4.6]*(t/h)/sqrt(W/h)
where,
epsilon(eff) = effective dielectric constant
epsilon(r) = dielectric constant
f = frequency
W = microstrip line width
h = height (of dielectric between ground and line)
t = microstrip line thickness
from Bahl & Bhartia "Microwave Solid State Circuit
Design"
Basically the wider and thinner the microstrip line,
the more of the field is contained in the dielectric,
beneath the trace and the higher the delectric and
slower the velocity of propagation. High impedance
(narrow) microstrip lines have more of their field in
the air, which also makes them more susceptible to
crosstalk.
Cheers,
Jeff LaT
-----Original Message-----
From: Tim Hochberg [mailto:tim.hochberg@xxxxxxxx]
Sent: Friday, July 18, 2003 7:06 AM
To: cclewell@xxxxxxxxxxxxxx; 'Peterson, James F
(FL51)';
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Finding Er (Permitivity)
Another issue is that, for microstrip, this is going
to give you the
effective dielectric constant, not the actual
dielectric constant. If
you can use stripline instead, this won't be a
problem, otherewise your
going to need to try to recover the dielectric
constant from the
effective dielectric constant. This will be a little
bit approximate
since the effective dielectric constant is frequency
dependant. However,
the dependence is week, and there are effective
dielectric calculators
floating around on the web, so you should be OK.
Regards,
Tim
Clewell, Craig wrote:
>Jim,
>
>I've got a big bat .
>
>You are correct...sorry about that.
>
>Thanks for the clarification.
>
>Craig
>
>-----Original Message-----
>From: Peterson, James F (FL51)
[mailto:james.f.peterson@xxxxxxxxxxxxx]
>Sent: Friday, July 18, 2003 9:25 AM
>To: cclewell@xxxxxxxxxxxxxx; 'kamal_elx@xxxxxxxxxxx'
>Cc: si-list@xxxxxxxxxxxxx
>Subject: RE: [SI-LIST] Re: Finding Er (Permitivity)
>
>
>craig,
>
>it might be a pretty big ballpark!!
>you would have to square the equation to get Er.
>
>Vp(m/s)= 3e8(m/s)/sqrt(Er)
>so
>Er = (3e8(m/s)/Vp(m/s))^2
>
>regards,
>Jim
>
>-----Original Message-----
>From: Clewell, Craig [ mailto:cclewell@xxxxxxxxxxxxxx
> ]
>Sent: Friday, July 18, 2003 8:40 AM
>To: 'kamal_elx@xxxxxxxxxxx'
>Cc: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Finding Er (Permitivity)
>
>
>Venu,
>
>If the board is a Microstrip you can do a quick
measurement of the delay and
>
>use this value to calculate the E'r.
>
>Use E'r = 3e8(m/s) / vp(m/s)
>
>where vp = propagation velocity = inverse of the
delay. This should get you
>
>in the ballpark
>
>Regards,
>
>Craig
>
>-----Original Message-----
>From: Kamal EC [ mailto:kamal_elx@xxxxxxxxxxx
>]
>Sent: Friday, July 18, 2003 7:25 AM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Finding Er (Permitivity)
>
>
>Hello Everybody,
>
>I am having a PCB Board for which I want to calculate
the Permitivity. I
>don't know what material is used for the pcb.
>I don't have any details of the board, except the
fabricated board.
>
>Is there any method by which i can calculate.
>
>Regards,
>Venu
>
>_________________________________________________________________
>It's new, it's here! It's full of fun!
>http://server1.msn.co.in/sp03/messengerpromo/index.asp
> MSN Messenger V6.0
>
>
>------------------------------------------------------------------
>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
>
>------------------------------------------------------------------
>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
>
>
>
>
>------------------------------------------------------------------
>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
>
>
>
>
>
------------------------------------------------------------------
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
------------------------------------------------------------------
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
---------------------------------
Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!
------------------------------------------------------------------
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
__________________________________
Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!
http://sbc.yahoo.com
------------------------------------------------------------------
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:
