Re: [SI-LIST] : HSTL termination

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From: Ken Church (kchurch@amcc.com)
Date: Thu Oct 26 2000 - 14:25:28 PDT


It sounds like you have used a single high current power supply for all
of your 0.75V requirements. If the 0.75V supply was close to ideal,
then it would have to sink current as well as source it. Was this the
case in your design? Have you ever used some kind of regulator to
terminate into 0.75V? I haven't seen a regulator that was 0.75V and/or
that could sink current. Maybe I can find one somewhere. Either that
or design one myself, but I'd like to avoid that.

Ken

P.S. We're not using IBM's HSTL I/O pads on this project.

Bo wrote:
>
> Hi Ken,
>
> I have used several different hstl I/O pads. Depending on the quality of I/O
> pads you are using you might be able to get away with series termination on the
> driver. I have used several HSTL technologies that could not do series
> termination in the worst case conditions. The recommended way is to use 50 Ohm
> parallel termination at the receiver(this will typically give you a good clean
> signal). Try other values for the resistor that will change your power supply
> requirements (which may help you to get your power supply cicruit to work).
> One other note, make sure that your 0.75V power supply is really clean. This
> power supply will go to the comparator inside of the pad. You can imagine what
> will happen if this voltage is not constant(I had this problem on my chip that
> was using HSTL pads).
> Regards,
> Bo
>
> p.s. From what I can guess you are probably using IBM's HSTL I/O pads(those are
> commonly used by people at your company). Am I correct?
>
> --- Ken Church <kchurch@amcc.com> wrote:
> > Hey,
> >
> > Does anybody have any experience with HSTL Class 1 termination? The
> > problem is determining a method of generating a good .75V source that
> > can source and sink current. Has this typically been a problem? Or is
> > there already a neat and cleaver way that is commonly used?
> >
> > Regards,
> >
> > Ken Church
> >
> >
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