[SI-LIST] Re: The crosstalk of transmission line when it is completelymatched
- From: "Zhiping Yang" <zhiping@xxxxxxxxx>
- To: <mherndon@xxxxxxxxx>, <zhang_kun@xxxxxxxxxx>
- Date: Mon, 9 Dec 2002 12:11:36 -0800
Hi Matthew,
For the relationship between self and mutuak inductane/capacitance, it is
always true for stripline because it is completely surrounded by homogeneous
media. For the microstrip, the surrounding media is inhomogeneous, so the
equation doesnot hold. Thanks.
Zhiping
----- Original Message -----
From: "Matthew Herndon" <mherndon@xxxxxxxxx>
To: <zhang_kun@xxxxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Sent: Monday, December 09, 2002 11:52 AM
Subject: [SI-LIST] Re: The crosstalk of transmission line when it is
completelymatched
>
> Zhangkun -
>
> Your question is timely for me: on Friday, I submitted a paper for
> January's DesignCon on the topic of Near-end crosstalk (NEXT), so I
> have been thinking about these issues.
>
> When I run the circuit in your first posting (Dec 5, 2002), I do indeed
> get puzzling results - FEXT looks the same as NEXT, except delayed. To
> check things out, I terminated each node of the transmission line
> individually. When I did so, I got the results I (and the textbooks)
> expect. See the PS below for exact details.
>
> I am not familiar with the termination scheme you used on the far end.
> Perhaps you (or someone on the list) can explain it to me, but I think
> it is the problem.
>
> On your question about FEXT: both inductive and capacitive coupling
> cause crosstalk. These factors add for NEXT and subtract for FEXT. Good
> references on this topic are: Hall, Hall and McCall "High-Speed Digital
> System Design" and Young "Digital Signal Integrity". The relevant
> formulas are (see PPS below for a definition of the symbols):
>
> Vpeak(NEXT) = (Vin/4)*(Lm/L + Cm/C)
> Vpeak(FEXT) = -(Vin*Tf/Tr)*(Lm/L - Cm/C)
>
> In your case, Lm/L is 0.1868 and Cm/C is 0.1875, so FEXT is (nearly) 0.
> I have been playing around with this phenomenon some. I only did a few
> simulations, but the property holds for all stripline cases I tried. I
> varied er, trace impedance, and even tried an asymmetrical stackup.
>
> Does anyone know if this property holds for all stripline, and if so
> why?
>
> BTW, the property does not hold for microstrip.
>
> -matt
> Matt Herndon
> ECAD Group
> Apple Computer, Inc.
>
> PS - Exact details and results of termination changes I made: I
> terminated out1 with a 47.69 Ohms to ground, and did the same with
> out2, and (taking Scott's suggestion) put a 47.69 Ohm resistor between
> the source and in1. The results from this circuit are more what I (and
> the textbooks) expect: Looking at in2 at the first NEXT pulse, which
> starts at the same time as the agressor pulse (1000psec), we see it has
> a rise time which is the same as the agressor (1000psec), then stays
> flat ("saturated") until two flight times have elapsed from the start
> of the agressor pulse (i.e., 1700 psec have elapsed), then returns to
> zero after another 1000psec . The pulse has the same polarity as dV/dt
> on the agressor. We see the same thing repeated on the downward
> transition 1300psec later. If anyone wants my netlist, I can send it.
>
> PPS - Symbols in the equations: Vin is the amplitude of the agressor
> pulse (assumed PWL), Tf is the flight time, Tr is the rise time of the
> aggressor pulse (assumed triangular), Lm is the inductive coupling of
> the traces (6.40120e-08 in your rlgc file), L is the self-inductance
> of the line (3.42622e-07), Cm is the capacitive coupling (2.82540e-11)
> and C is the (total?) capacitance (I believe you can use 1.50678e-10
> for this, there is some confusion about whether this number in HSPICE
> is total capacitance or self-capacitance - perhaps someone can
> clarify). Lm, L, Cm, and C are per unit length, of course.
>
> On Sunday, December 8, 2002, at 06:53 PM, Zhangkun wrote:
>
> >
> > Hi McMorrow
> >
> > I do not agree with you. Please try the following netlist. The far-end
> > crosstalk is zero.
> >
> > match_1.sp
> > the simple diff transmissionline
> > .options list node post
> > .op
> > .tran 0.5n 100n
> > *driver
> > vp in1 gnd pulse 0 5 1n 1n 1n 3n 8n
> > *vn in2 gnd pulse 10 0 1n 1n 1n 3n 8n
> > *transmission line
> > Wcable in1 in2 gnd out1 out2 gnd RLGCfile=diffline.rlgc n=2 l=5000mil
> > *receiver
> > rin2 in2 gnd 47.69
> > rout1 out1 gnd 47.69
> > rout2 out2 gnd 47.69
> > .end
> >
> > The difference is the terminal at the farend. There is no difference
> > at near end.
> >
> > Best Regards
> > Zhangkun
> > 2002.12.09
> >
> > ----- Original Message -----
> > From: Scott McMorrow <scott@xxxxxxxxxxxxx>
> > To: <zhang_kun@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > Sent: Friday, December 06, 2002 11:38 AM
> > Subject: Re: [SI-LIST] The crosstalk of transmission line when it is
> > completelymatched
> >
> >
> >> Zhangkun,
> >>
> >> You are getting reflected reverse crosstalk off of the driver. You
> >> will
> >> need to match the driver impedance to the transmission line impedance
> >> to
> >> eliminate this reflection. Since the driver is a perfect source, your
> >> reflection coefficient is -1.
> >>
> >> scott
> >>
> >> --
> >> Scott McMorrow
> >> Teraspeed Consulting Group LLC
> >> 2926 SE Yamhill St.
> >> Portland, OR 97214
> >> (503) 239-5536
> >> http://www.teraspeed.com
> >>
> >>
> >>
> >>
> >>
> >>
> >> Zhangkun wrote:
> >>
> >>> Hi all:
> >>>
> >>> This morning, I do some crosstalk simulation. I find something
> >>> interesting. The following is what I do.
> >>>
> >>> 1. Create diffline.rlgc from rlgc.sp
> >>> 2. Calculate the Z_diff and Z_comm from diffline.rlgc
> >>> 3. Match the diffline and simulate it by match_2.sp
> >>>
> >>> I find the near end crosstalk and the far end crosstalk are equal.
> >>> This is not same to the general crosstalk theory. I want to know >>>
why.
> >>>
> >>> rlgc.sp
> >>> .OPTION PROBE POST
> >>> VIMPULSE in1 gnd PULSE 0v 5v 5n 2n 2n 20n
> >>> W1 in1 in2 gnd out1 out2 gnd FSmodel=cond2_sys N=2 l=1000mil
> >>> Rin2 in2 gnd 49
> >>> Rout1 out1 gnd 49
> >>> Rout2 out2 gnd 49
> >>> .MATERIAL diel DIELECTRIC ER=4.5
> >>> .SHAPE rect RECTANGLE WIDTH=7mil, HEIGHT=2mil,
> >>> .LAYERSTACK stack1,
> >>> +LAYER=(PEC,20mil), LAYER=(diel,22mil),
> >>> +LAYER=(PEC,20mil)
> >>> .FSOPTIONS opt1 PRINTDATA=YES
> >>> .MODEL cond2_sys W MODELTYPE=FieldSolver,
> >>> +LAYERSTACK=stack1, FSOPTIONS=opt1
> >>> +RLGCFILE=diffline.rlgc
> >>> +CONDUCTOR=(SHAPE=rect, ORIGIN=(0,30mil)),
> >>> +CONDUCTOR=(SHAPE=rect, ORIGIN=(14mil,30mil))
> >>> .TRAN 0.5n 100n
> >>> .PROBE v(out1)
> >>> .END
> >>>
> >>> diffline.sp
> >>> *SYSTEM_NAME : cond2_sys
> >>> *
> >>> * ------------------------------------ Z = 0.0015748
> >>> * //// Top Ground Plane //////////////
> >>> * ------------------------------------ Z = 0.0010668
> >>> * diel H = 0.0005588
> >>> * ------------------------------------ Z = 0.000508
> >>> * //// Bottom Ground Plane ///////////
> >>> * ------------------------------------ Z = 0
> >>>
> >>> * N (number of signal conductors)
> >>> *********************************
> >>> 2
> >>>
> >>> * Lo (H/m)
> >>> *********************************
> >>> 3.42622e-07
> >>> 6.40120e-08 3.42622e-07
> >>>
> >>>
> >>> * Co (F/m)
> >>> *********************************
> >>> 1.50678e-10
> >>> -2.82540e-11 1.50678e-10
> >>>
> >>>
> >>> * Ro (Ohms/m)
> >>> *********************************
> >>> 0.00000e+00
> >>> 0.00000e+00 0.00000e+00
> >>>
> >>>
> >>> * Go (S/m)
> >>> *********************************
> >>> 0.00000e+00
> >>> -0.00000e+00 0.00000e+00
> >>>
> >>> match_2.sp
> >>> the simple diff transmissionline
> >>>
> >>> .options list node post
> >>> .op
> >>> .tran 0.5n 100n
> >>>
> >>> *driver
> >>> vp in1 gnd pulse 0 5 1n 1n 1n 3n 8n
> >>> *vn in2 gnd pulse 10 0 1n 1n 1n 3n 8n
> >>> rin2 in2 gnd 47.69
> >>>
> >>> *transmission line
> >>> Wcable in1 in2 gnd out1 out2 gnd RLGCfile=diffline.rlgc n=2 l=5000mil
> >>>
> >>> *receiver
> >>> rout1 out1 node1 39.4598
> >>> rout2 out2 node1 39.4598
> >>> rcon node1 gnd 9.0864
> >>>
> >>> .end
> >>>
> >>> Z_diff=78.9195 Z_comm=28.8163
> >>> rou1=rout2=Z_diff/2
> >>> rcon=(2*Z_comm-Z_diff/2)/2
> >>>
> >>> Best Regards
> >>> Zhangkun
> >>> 2002.12.06
> >>>
> >>>
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> >>
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