Subject: Re: [IBIS-Users] LVDS RECEIVER TERMINATION Question
From: Kevin Fisher (kfisher@sisoft.com)
Date: Fri Jul 26 2002 - 18:29:10 PDT
All,
One technique we have used for terminated LVDS receivers is to model
the differential termination behavior in the power clamp and ground
clamp curves themselves. The setup for this technique is similar to a
popular technique for LVDS drivers: tie the sweeping DC voltage source
(v_sweep) to the p-pad, tie a VCVS equal to v_sweep and a gain of -1 on
the n-pad (v_sweep_bar) and bias both pads at the desired common mode
voltage.
Modeling termination using this approach can also be applied to
single-ended receivers that have termination on-die. We have had success
using IBIS models generated with this technique in various simulators
because it uses only basic IBIS syntax. As Hazem points out though, IBIS
models generated for a certain Vcm is limited to nets where the common
mode voltage doesn't vary from the one used to model the receiver.
We are currently looking into other possible solutions that are portable
across multiple simulators and don't have the Vcm limitation.
Hope this helps.
-- Kevin M. Fisher Consultant Signal Integrity Software Inc. 6 Clock Tower Place, Suite 250 Maynard, MA 01754 Phone: (978) 461-0449, ext 11 http://www.sisoft.comHegazy, Hazem wrote: > Hi, > Yes, it's not supported in SOME simulators but not all. > The Rdiff/2 to certain CM voltage might be a good solution if the common > mode voltage itself doesn't change with different loads. I've seen a lot > of LVDS driver with common mode voltage changes with the differential > load value. I don't see if this applicable in the receiver case or not, > I'm just saying the one should be careful. > > BR, > > > -----Original Message----- > From: rob.mataheroe@philips.com > To: Hegazy, Hazem > Cc: 'Hassan Ali '; 'ibis-users@server.eda.org '; > owner-ibis-users@server.eda.org; 'Peter LaFlamme ' > Sent: 7/25/02 4:10 PM > Subject: RE: [IBIS-Users] LVDS RECEIVER TERMINATION Question > > Hello All, > > R Series appears to be not supported by the Ibis simulators, which is a > shame, since it has been prepared so well in Ibis 3.2 > > What do you think about the following approach: > Use a resistor of Rdiff/2 to a fixed point at the level of the desired > common mode voltage. > This could be achieved by using the model Terminator and using Rgnd and > Rpower. > > Looking forward to your reactions, > > Rob > ________________________________________________________________________ > __ > Rob Mataheroe > Philips Semiconductors bv > P.G. Logic Product Group PD&S > Building AM1.108 > Senior Design Modeling Engineer > Gerstweg 2 > Tel. ++31 (0)24 353 2370 > 6534 AE Nijmegen > Fax. ++31 (0)24 353 2820 > The Netherlands > Email: Rob.Mataheroe@philips.com > Seri: matahero@nyhp04 > > > > > > > > > "Hegazy, Hazem" > > <hazem_hegazy@mentor To: "'Peter > LaFlamme '" <plaflamm@amcc.com> > > g.com> "'Hassan Ali '" > <Hassan.Ali@fidus.ca> > Sent by: cc: > "'ibis-users@server.eda.org '" <ibis-users@server.eda.org> > > owner-ibis-users@ser (bcc: Rob > Mataheroe/NYM/SC/PHILIPS) > > ver.eda.org Subject: RE: > [IBIS-Users] LVDS RECEIVER TERMINATION Question > > > Classification: > > 07/23/02 11:01 PM > > > > > > > > > > Hi, > I've a solution...I didn't test it yet but, I suggest that based on an > old solution of mine for 100 terminated LVDS DRIVERS in IBIS summit Jan > 2001 "hegazy.pdf or zip on IBIS home page". > > > In the driver case, I consider the internal termination as a part of the > buffer itself, I could not take it away "In some cases we can" so, I > want to get the I-V characteristics based on this. > > > What are the I-V characteristics? Simply, it's the steady state solution > of the voltage and current at all possible loads. > > > So, I put a resistor between P node and N node and measure "steady state > voltage and current" now, vary the resistor value from zero to infinity > (open circuit) and do the same extraction to complete your I-V table. > You will have the actual behavior of the > buffer (Interactive) on all possible loading conditions. This is > verified with a lot of LVDS buffers for very famous customer. > > > For the receiver we can't do that as there is no source of current like > in the driver case to measure the I and V. > So, my suggestion is to put a voltage source between the p and n nodes > (differential voltage source). Vary the voltage source value in normal > DC analysis and measure the P voltage with the current through the > voltage source to form the I-V table with the > interaction of the n node inherited inside it. > > > I'll try this solution with some validation and keep you all informed. > I might have goofed!! > > > BR, > > > > > > -----Original Message----- > From: Peter LaFlamme > To: Hassan Ali > Cc: ibis-users@server.eda.org > Sent: 7/23/02 6:52 PM > Subject: Re: [IBIS-Users] LVDS RECEIVER TERMINATION Question > > > Hi Hassan, > Thanks alot for the comments and information. I have done the same thing > previously in simulations. I have also received input models that had > the internal termination modeled as a dynamic clamp. In comparisons > between dynamic clamp modeled terminations > and your method, I found that (just in my case) there was not real good > correlation. > > > Regards, > Peter > > > Peter LaFlamme > > > Applied Micro Circuits Corp. > System Applications Engineer > 200 Minuteman Rd, 3rd Floor > Andover, MA 01810 > > > 978-247-8470 phone > 978-623-0055 Fax > > > > > > Hassan Ali wrote: > > > > Hi Peter, > > > > I had the same situation a few months ago and I only had to go with an > > adhoc solution. > > > > Yes indeed most simulators do not have good support for differential > > models with [R Series] termination. I ended up creating a single-ended > > input buffer model (same for the P and N side) with no termination > > between P and N sides. This only captured the clamping function. > > > > In my simulation I had to recreate the terminated differential input > > buffer by using two single-ended buffers (one for the P and one for > the > > N pin) with a termination resistor tied between them. The package > > parasitics were also tied to the two pins. I manually changed the > values > > of the termination resistor and package parasitics to cover their > > variation in the typical, minimum and maximum corners. > > > > Probably there is a better solution, but that's what I did as a > > quick-and-dirty work-around. > > > > Regards. > > > > Hassan. > > > > Hassan Ali, Ph.D. > > Signal Integrity Specialist -Talented, innovative designers > > Fidus Systems Inc. -Highly competitive rates > > Tel: (613) 828-0063 Ext.342 -Fixed-price business model > > Fax: (613) 828-3113 -State-of-the-art design tools > > http://www.fidus.ca -Customer-friendly attitude > > > > -----Original Message----- > > From: Peter LaFlamme [mailto:plaflamm@amcc.com] > > Sent: Tuesday, July 23, 2002 9:01 AM > > To: ibis-users@eda.org > > Subject: [IBIS-Users] LVDS RECEIVER TERMINATION Question > > > > Hi All, > > I am tasked with creating an IBIS model for an LVDS receiver cell that > > has an internal 100 ohm termination between the P and N nodes. I had > > asked Bob Ross about this a while ago and as usual he was very > helpful. > > >From his response I used the following > > implementation: > > > > |**************************************************************** > > | Component: LVDSRCV > > |**************************************************************** > > | > > [Component] LVDSRCV > > [Manufacturer] AMCC > > | > > | > > | > > [Package] > > | variable typ min max > > R_pkg 1E-3 NA NA > > L_pkg 1E-9 NA NA > > C_pkg 1E-12 NA NA > > | > > [Pin] signal_name model_name R_pin L_pin C_pin > > 1 PAD lvdsrcv NA NA NA > > 2 PADN lvdsrcv NA NA NA > > | > > [Series Pin Mapping] pin_2 model_name function_table_group > > 1 2 rterm_100 > > > > | > > [Diff_pin] inv_pin vdiff tdelay_typ tdelay_min > > tdelay_max > > | > > 1 2 0.2 0 0 > 0 > > > > [Model] rterm_100 > > C_comp 0.1pF 0.1pF 0.1pF > > > > Model_type Series > > |variable R(typ) R(min) R(max) > > [R Series] 100 80 120 > > > > [Temperature Range] 25.00 125.00 0.00 > > [Voltage Range] 1.800 1.650 1.950 > > > > > ************************************************************************ > > **************** > > > > I was able to get the model past the IBIS checker but my simulations > did > > not show the 100 ohm terminator. I was using a tool which I believe > does > > not support this implementation (no need to mention names). I have > seen > > other implementations where I believe > > > > a "Dynamic clamp" is used to model the termination behavior, but I am > > unsure. Can anyone guide me to some reference material or weigh in > with > > your experience or help. > > > > Thanks alot, > > Peter > > > > > > > > -- > > Peter LaFlamme > > > > Applied Micro Circuits Corp. > > System Applications Engineer > > 200 Minuteman Rd, 3rd Floor > > Andover, MA 01810 > > > > 978-247-8470 phone > > 978-623-0055 Fax > > |------------------------------------------------------------------ > > |For help or to subscribe/unsubscribe, email majordomo@eda.org > > |with just the appropriate command message(s) in the body: > > | > > | help > > | subscribe ibis <optional e-mail address, if different> > > | subscribe ibis-users <optional e-mail address, if different> > > | unsubscribe ibis <optional e-mail address, if different> > > | unsubscribe ibis-users <optional e-mail address, if different> > > | > > |or email a written request to ibis-request@eda.org. > > | > > |IBIS reflector archives exist under: > > | > > | http://www.eda.org/pub/ibis/email_archive/ Recent > > | http://www.eda.org/pub/ibis/users_archive/ Recent > > | http://www.eda.org/pub/ibis/email/ E-mail since 1993 > > > -- > > > > > > > > > |------------------------------------------------------------------ > |For help or to subscribe/unsubscribe, email majordomo@eda.org > |with just the appropriate command message(s) in the body: > | > | help > | subscribe ibis <optional e-mail address, if different> > | subscribe ibis-users <optional e-mail address, if different> > | unsubscribe ibis <optional e-mail address, if different> > | unsubscribe ibis-users <optional e-mail address, if different> > | > |or email a written request to ibis-request@eda.org. > | > |IBIS reflector archives exist under: > | > | http://www.eda.org/pub/ibis/email_archive/ Recent > | http://www.eda.org/pub/ibis/users_archive/ Recent > | http://www.eda.org/pub/ibis/email/ E-mail since 1993 >
-- Kevin M. Fisher Consultant Signal Integrity Software Inc. 6 Clock Tower Place, Suite 250 Maynard, MA 01754 Phone: (978) 461-0449, ext 11 http://www.sisoft.com
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