Re: LVDS models and s2ibis2

Hi,

Could you please specify the titles of the presentation you mentioned?
Where can I get them? Thanks.

Zhiping

"Hegazy, Hazem" wrote:

>
>
> Hi,
>
> As The presentation shows, we classify LVDS buffer into two
> categories:
>
> - Without internal termination: (If we are lucky)
> - This one I consider it just a normal differential
> buffer. No special setting for it, just the normal differential
> buffers settings.
>
> - With internal termination: (The usual received sub circuit)
> - If the internal termination (the resistance shunted
> between the +ve & -ve PADS) has a discrete value (and a linear one)
> then you can use the approach of decomposing the resistance behavior
> as shown in Munich summit meeting presentation.
>
> - If the termination is not linear or you can't specify
> its value then you can use the variable resistance approach in the
> presentation you already have.
>
> Regarding your questions:
>
> >>>> 1. If differential inputs or outputs
> switch between 1.1 and 1.3 volts, what
> range of voltages do you use for the I/V
> curves?
>
> The IBIS standard recommends the I-V curves extraction from -VDD to
> 2*VDD But if you have difficulties in that you can sweep in the active
> region only (from 0 to VDD) in this case you should expect bad
> validation out of the DC range (if you have some high reflection
> above/under VDD/zero respectively).
>
> >>>> 2. What load do you use on differential
> outputs to generate the V/T curves? (What
> are Rfix, Rref, Vref, ... and how are these
> plus the terminating resistor connected?)
> By the way, this has to be done in a way
> that HPSICE converges.
>
> The loads are normally 50 Ohm to the reference voltage. Apparently the
> reference voltage in your case is 1.2 volt as the wave form swings
> between 1.1 & 1.3 (i.e. around 1.2) .
>
> Rfix is the load you but while extracting the V-T tables, Rref&Vref
> are the value of the timing test loads stated in the data sheets of
> that buffer.
>
> BR,
>
> Hazem Hegazy
> Development Engineer
>
> Tel: (20 2) 4135458
> Fax: (20 2) 4186945
> Mobile: (+20) 105129341
> Email: hazem_hegazy@mentor.com
>
> -----Original Message-----
> From: Greg Haynes [mailto:haynes@utmc.aeroflex.com]
> Sent: Saturday, May 26, 2001 1:23 AM
> To: ibis-users@eda.org
> Subject: LVDS models and s2ibis2
>
> I'm trying to create IBIS models for some
> parts that we make using s2ibis2, and for
> single-output buffers it works pretty well.
> LVDS buffers are another story. In some
> cases I've had a little success, but I
> don't know if s2ibis2 is even supposed to
> be capable of creating the required SPICE
> decks for simulating LVDS buffers.
>
> From a previous post I was referred to
> a presentation on LVDS modeling by
> Hegazy and Korany, but it's just foils
> with no detailed explanations.
>
> Among my questions:
>
> 1. If differential inputs or outputs
> switch between 1.1 and 1.3 volts, what
> range of voltages do you use for the I/V
> curves?
> 2. What load do you use on differential
> outputs to generate the V/T curves? (What
> are Rfix, Rref, Vref, ... and how are these
> plus the terminating resistor connected?)
> By the way, this has to be done in a way
> that HPSICE converges.
>
> --
> Greg Haynes haynes@utmc.aeroflex.com
> Aeroflex UTMC Microelectronic Systems
> 4350 Centennial Blvd phone: 719 594-8197
> Colorado Springs, CO 80907 fax: 719 594-5541

--
   Zhiping Yang, Ph. D.
   Hardware Engineer
   Cisco Systems
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