[SI-LIST] Re: What to do with "isolation" conductors in ribbon cable?
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: <stephen.blake@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 2 Oct 2007 17:46:31 -0700
Thanks Stephen,
This agrees with my simulation results (deck below) - I think grounding
the conductors at both ends offers the best isolation (unless someone
can find a fault in my sim). (Change the value of
R_isolation_in/R_isolation_out to 50 to test the "terminate at Z0"
case).
_______________________________
Ribbon Cable isolation investigation w/ 0 ohm at isolation
.param ribbon_L=3D2.5
.param vhi=3D2
.param tr =3D35p
.param pw=3D5n
.param per=3D1000n
=20
.AC Lin 800 30K 20G
.tran 1p 10n
******* Internal Field Solver Stuff **********
.MATERIAL fr4 DIELECTRIC ER=3D4.2 LOSSTANGENT=3D.018
.MATERIAL copper METAL CONDUCTIVITY=3D4.2E07
.FSOPTIONS myoptions ACCURACY=3DHIGH PRINTDATA=3DYES=20
+ COMPUTEG0=3DYES COMPUTEGD=3DYES COMPUTER0=3DYES
COMPUTERS=3DYES
** solve for G0, Gd, R0, Rs
*** ribbon cable ***
.LAYERSTACK ribbon_stack
+ LAYER=3D(fr4,'.0254*40e-3'), $ FR4 insulator, 1 mm (per
mechanical dwg, rounded from 39.37 to 40 for simplicity)
+ LAYER=3D(air, '.0254*199e-3'), $ separate gnd and conductors
by 200 mils
+ LAYER=3D(PEC,'.0254*1e-3'), $ GND plane, 1mils
* NOTE: center of conductor should be at 220
.SHAPE s1_cond CIRCLE RADIUS=3D'.0254*10e-3' $ 10 mil radius
.MODEL s1_Tline W MODELTYPE=3DFieldSolver LAYERSTACK=3Dribbon_stack
+ FSOPTIONS=3Dmyoptions RLGCFILE=3Ds1_Tline.rlgc
+ CONDUCTOR=3D(SHAPE=3Ds1_cond,=20
+ ORIGIN=3D('.0254*0'
,'.0254*220e-3'),
+ MATERIAL=3Dcopper)
+ CONDUCTOR=3D(SHAPE=3Ds1_cond,=20
+ ORIGIN=3D('.0254*40e-3'
,'.0254*220e-3'),
+ MATERIAL=3Dcopper)
+ CONDUCTOR=3D(SHAPE=3Ds1_cond,=20
+ ORIGIN=3D('.0254*80e-3'
,'.0254*220e-3'),
+ MATERIAL=3Dcopper)
**** ribbon stimulus at port 1
V_src N_src GND PULSE (0 vhi 0N tr tr pw per) AC =3D vhi
R_src N_src N_p1 R=3D50
R_isolation_in N_ribbon_isolation_in GND R=3D0.0001
R_victim_in N_ribbon_victim_in GND R=3D50
T_src N_p1 GND N_ribbonag_in GND Z0=3D50 TD=3D180p
W_ribbon N_ribbonag_in N_ribbon_isolation_in N_ribbon_victim_in GND
N_ribbonag_out N_ribbon_isolation_out N_ribbon_victim_out GND
+ FSmodel=3Ds1_Tline N=3D3 L=3D'.0254*ribbon_L'
T_out N_ribbonag_out GND N_load GND Z0=3D50 TD=3D180p
R_isolation_out N_ribbon_isolation_out GND R=3D0.0001
R_victim_out N_ribbon_victim_out GND R=3D50
R_load N_load GND R=3D50
.END
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of stebla01
Sent: Tuesday, October 02, 2007 12:44 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: What to do with "isolation" conductors in ribbon
cable?
I've simulated this situation to look at the effect of inductively
coupled noise into the ribbon cable. Each signal conductor was adjacent
to a spare conductor. The result of the simulation was that the spare
conductors should be tied to ground at both ends and that the
inductively coupled noise was smallest on the signal conductors nearest
the centre of the ribbon cable. However, in my case the inductive noise
was at 20kHz and so the cable much less that a wavelength so I did not
model the ribbon cable as a transmission line. However, it seems to me
that the idea is to use the spare conductors to try to approximate a
ground plane made out out a mesh of discrete wires; hence connecting the
spare conductors to ground would still make sense at higher frequency.
Stephen
=20
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=20
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