RE: [SI-LIST] : PECL TO LVPECL

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From: Degerstrom, Michael J. (degerstrom.michael@mayo.edu)
Date: Fri Apr 27 2001 - 10:44:48 PDT


Larry,

My recollection was that the voltage levels are about .9V
and 1.7V below VCC for HIGH and LOW levels, respectively.
This was true for PECL with VCC=+5 and +3.3 but it seemed
to me that there was some deviation of this rule of
thumb for VCC=2.5V.

Gary - I was able to generate (nearly) LVDS swings from a 3.3V PECL.
To do this I terminated the driving pin with an 80 ohm and
then a 100 ohm resistor to ground. The pcb trace tapped
between the two resistors and then connected the receiving
pin. There was no 50 ohm to VTT termination at the receiver pin.
If you use a 50 ohm pcb trace then the parallel combination
of the 100 ohm and the 80 ohm (adding several more ohms for
the emitter follower impedance) was quite adequate for
providing source impedance matching for your pcb trace. I never
really got a chance to build this but the simulations
were very promising.

At any rate I would think that using this same approach you
would be able to get 3.3V PECL levels from a 5V PECL part. You
will probably have to bump up the 100 ohm resistor while lowering the
80 ohm resistor so you don't pull too much current and over-
heat you driver. Probably a 180 and ~65 ohm combination
will do. Your swings will drop to about 650mv p-p and
your HIGH state will be around 3.3V. This will probably
work fine if you are driving 3.3V PECL if it is a bipolar
technology. But if you really need true 3.3V PECL levels
then you need a translator part or you can AC couple
if you data is DC balanced.

Mike

_______________________________________________________________
Mike Degerstrom Email: degerstrom.michael@mayo.edu
Mayo Clinic; 200 1st Street SW ; Rochester, MN 55905
Phone: (507) 538-5462 FAX: (507) 284-9171
WWW: http://www.mayo.edu/sppdg/sppdg_home_page.html
_______________________________________________________________

> -----Original Message-----
> From: Larry Miller [mailto:ldmiller@rhapsodynetworks.com]
> Sent: Friday, April 27, 2001 10:58 AM
> To: 'Steinkogler, Gary'; 'si-list@silab.eng.sun.com'
> Subject: RE: [SI-LIST] : PECL TO LVPECL
>
>
> I guess we have to assume that you are not able to
> capacitively couple the
> signals. The signal amplitudes are about the same for both
> flavors, but the
> DC levels differ. True?
>
> Larry Miller
>
> -----Original Message-----
> From: Steinkogler, Gary [mailto:gsteinkogler@opticalsolutions.com]
> Sent: Friday, April 27, 2001 6:53 AM
> To: 'si-list@silab.eng.sun.com'
> Subject: [SI-LIST] : PECL TO LVPECL
>
>
>
> Anybody know of 5V PECL to 3.3V LVPECL Translators - single or dual
> translator. I know ON Semi - MC100LVEL92 and Micrel -
> SY100EL92 make one,
> but these are triple translators.
>
> Gary
>
> Gary Steinkogler
> Optical Solutions
> 16305 36th Ave. North
> Suite 300
> Minneapolis, MN 55446-2698
> Phone: (763) 268-3633
> Fax: (763) 268-3301
> Main: (763) 268-3300
>
> email:gsteinkogler@opticalsolutions.com
>
>
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