[SI-LIST] Re: [!! SPAM] Re: plane RLGC Debye model
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: Istvan Novak <istvan.novak@xxxxxxx>
- Date: Mon, 17 Nov 2008 09:30:53 -0500
I'm going to add to Istvan Novak's comments on causality of plane
structures. Even with time domain analysis, with all of the possible
signal, power, power-coupling coupling, via-plane coupling, and
signal-signal coupling paths, causality of the power plane pair
simulations is generally a non-issue. Signal traces do not follow the
minimum distance straight line route from Tx to Rx. Neither does
signal-signal coupling. But, via-power, power-power, coupling does
follow the minimum radial distance path between a Tx and an Rx. It is
therefore possible for coupled energy to arrive at the destination prior
to signal arrival, showing what appears to be non-causal Rx waveforms,
where noise occurs prior to the expected rising edge. This can occur
EVEN when there is only one signal measured or analyzed, and one power
plane pair, if the signal vias transition through the planes.
IMO non-causal variations in group delay, due to modeling of the planes,
is insignificant relative to all the other potential causal phase delay
variations of multiple sources in a real system.
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
Istvan Novak wrote:
> Hi Istvan,
>
> In my experience it has not yet been necessary to use full causal plane
> models for power distribution designs. If you want to characterize
> materials accurately, yes, it is needed.
>
> For successful PDN designs at most you need is the skin resistance and
> DC resistance. Capacitance, inductance and conductance also change with
> frequency, but if you ignore those frequency dependencies, a good PDN
> still will be fine. Reason: these frequency dependencies primarily
> impact resonance frequencies and time-of-flight parameters. In a good
> PDN you want to suppress resonances anyway, so their very exact
> frequency matters less. Time of flight would matter only if we wanted
> to simulate time-domain waveforms accurately; this, however, would
> require the accurate knowledge of time-domain excitation current data,
> which is seldom if at all is available.
>
> If for reasons of curiosity you are still interested in simulating
> frequency dependent plane models in free Berkeley SPICE, you can simply
> run SPICE in batch mode, create the frequency dependent parameters for a
> given frequency, run SPICE at that single frequency, read in the result,
> change frequency and repeat. That same solution also works if you want
> skin resistance only.
>
> Regards,
>
> Istvan Novak
> SUN Microsystems
>
> Istvan Nagy wrote:
>
>> hi
>>
>> thanks, this answers my question, but opens a new one.
>> "fit it with 3-4 real poles evenly distributed over you frequency band to
>> get rational approximation form"
>> -probably this would be the most difficoult part for me, i think. at least i
>> have no idea how to do it (theory, c program).
>> but probably its not a signal/power integrity problem already, but
>> mathematics.
>>
>> on chapter 7, you mean chapter 4.2.1.6, figure 4.6d ? ok, it doesnt matter.
>>
>> regards,
>> Istvan
>>
>>
>> ----- Original Message -----
>> From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
>> To: "'Istvan Nagy'" <buenos@xxxxxxxxxxx>; "'steve weir'" <weirsi@xxxxxxxxxx>
>> Cc: <si-list@xxxxxxxxxxxxx>
>> Sent: Saturday, November 15, 2008 7:48 PM
>> Subject: RE: [SI-LIST] Re: plane RLGC Debye model
>>
>>
>>
>>
>>> Istvan,
>>>
>>> If you have dielectric constant value at 1 MHz, dielectric constant at 20
>>> GHz may be about 10% smaller for a composite PCB material (as observed in
>>> multiple experiments). It may be not important for practical PDN design as
>>> Steve mentioned and simple 1-frequency approximation for G and C may work
>>> just fine. The same is valid for R and L. Though, in case of very closely
>>> spaces planes (with less than 5 mils distance), the effect of internal
>>> inductance of the metal planes in combination with the dielectric
>>> dispersion
>>> can cause significant shifts of resonances even at lower frequencies
>>> important for PDN design.
>>> If you want to build the lattice-type equivalent circuit model valid over
>>> 3-4 decades in frequency and accounting for frequency variations of
>>> dielectric constant and internal plane inductance, it can be done with the
>>> broadband transmission plane model (see my paper "Transmission plane
>>> models
>>> for parallel-plane power distribution system and signal integrity
>>> analysis"
>>> in proceedings of 22-nd ACES symposium, 2006, p. 382-389, also available
>>> at
>>> http://www.shlepnev.com/Publications/ACES2006c.pdf). The model is
>>> validated
>>> with experiments in I. Novak, J. Miller Frequency-domain characterization
>>> of
>>> power distribution networks - Artech House, 2007, chapter 7 and in J.
>>> Miller, G. Blando, B. Williams, I. Novak "Impact of PCB Laminate
>>> Parameters
>>> on Suppressing Modal Resonances" - DesignCon2008.
>>>
>>> Here are possible steps to build broad-band SPICE model for PDN:
>>> 1) Use equation (3) from the cited ACES paper for frequency-dependent
>>> admittance per square Ys and fit it with 3-4 real poles evenly distributed
>>> over you frequency band to get rational approximation form (9)
>>> 2) Use equation (11) for sheet impedance of the plane pair Zs and fit it
>>> with 3-4 real poles to get the rational approximation form (12)
>>> 3) Define cell size dx and dy for your equivalent lattice model
>>> 4) Compute admittance of one sell as Ys*dx*dy - the rational approximation
>>> from step 1 immediately gives you the second Foster form of GC or RC
>>> network
>>> for the cell node
>>> 5) Compute impedance of one sell as Zs*dx/dy for x-axis and as Zs*dy/dx
>>> for
>>> y-axis - the rational approximation from step 2 immediately gives you the
>>> second Foster form of RL network for the x and y branches of your cell
>>> 6) Combine cells into a 2D equivalent circuit of the plane pair
>>>
>>> Note that the final 2D model is similar to a lumped broad-band model for a
>>> transmission line.
>>>
>>> Best regards,
>>> Yuriy Shlepnev
>>> www.simberian.com
>>>
>>> -----Original Message-----
>>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>> On
>>> Behalf Of Istvan Nagy
>>> Sent: Saturday, November 15, 2008 4:45 AM
>>> To: steve weir
>>> Cc: si-list@xxxxxxxxxxxxx
>>> Subject: [SI-LIST] Re: plane RLGC Debye model
>>>
>>> hi
>>>
>>> the only thing what i have is the dielectric thickness, and Er@1MHz, as
>>> usual. i normally dont haave measurement data.
>>> the simple RLGC models dont take the frequency-dependeny of the Er into
>>> account, skin effect,...
>>> these can be described by simple equations, but how to kame a lumped model
>>> based on equations containing E^x... and similar things.
>>> at least these 2 effects should be included.
>>> Er(f)=Er(f0)*(jf/f0)^(-0.006366) this gives a frequency dependency for C
>>> and G
>>> R is dependent on f because of the skin effect.
>>> somehow L is also dependent on frequency?
>>>
>>> because it is for a unit-cell model, it shouldnt need more then very few
>>> parameters, like dielectric thickness, Er(f0), f, cell size.
>>>
>>> Istvan
>>>
>>> ----- Original Message -----
>>> From: "steve weir" <weirsi@xxxxxxxxxx>
>>> To: "Istvan Nagy" <buenos@xxxxxxxxxxx>
>>> Cc: <si-list@xxxxxxxxxxxxx>
>>> Sent: Saturday, November 15, 2008 12:29 PM
>>> Subject: [SI-LIST] Re: plane RLGC Debye model
>>>
>>>
>>>
>>>
>>>> Istvan what data do you have? Do you have measurements from material
>>>> samples?
>>>>
>>>> For most power work, it is sufficient to use a single value for tangent
>>>> loss. If you get the other parameters correct, then the models will
>>>> tend to show slightly higher peak impedances at the modal resonances
>>>> than measurements out above 1GHz, but the difference is typically not
>>>> great.
>>>>
>>>> Steve.
>>>> Istvan Nagy wrote:
>>>>
>>>>
>>>>> hi
>>>>> how can i calculate the Ri, Li, Gi, Ci parameters for a frequency
>>>>> dependent unit-cell Debye RLGC model for a power/gnd plane pair? 1st
>>>>> order or up to 3rd order Debye model would be good.
>>>>> are there any equations?
>>>>> (Debye models introduce additional RL and GC elements into the 4 element
>>>>> original RLGC model to reflect the frequency-dependency, and with
>>>>> staying
>>>>>
>>>>> with basic circuit elements, suitable for spice)
>>>>>
>>>>> i would like to make frequency dependednt spice 3f5 models (not
>>>>> w-element
>>>>>
>>>>> model, since its not compatible with most of the spices) from arbitrary
>>>>> power planes, with lumped-element grid.
>>>>> I found application notes where in the examples they just shown the
>>>>> calculated values, without describing the calculation.
>>>>>
>>>>> regards,
>>>>> Istvan Nagy
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> --
>>>> Steve Weir
>>>> Teraspeed Consulting Group LLC
>>>> 121 North River Drive
>>>> Narragansett, RI 02882
>>>>
>>>> California office
>>>> (866) 675-4630 Business
>>>> (707) 780-1951 Fax
>>>>
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>>>> (401) 284-1827 Business
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