From: sweir ([email protected])
Date: Fri Nov 05 1999 - 10:36:27 PST
Eric,
I was not proposing the GAL as a clock buffer, but as the MUX/FF
combination at 120MHz, for which it is still in its operational limits. I
don't know of any single-ended part that is going to do TTL at 240MHz.
Regards,
Steve.
At 10:30 AM 11/5/99 -0800, you wrote:
>Jason Zheng wrote:
> >
> > > Be careful if you intend to use an inverter as a clock buffer. The alvc
> > > stuff is pretty fast, but not nearly fast enough for your needs. That
> > > particular part is about 4nS spec into a heavy load, and a minimum
> Tpd spec
> > > of 1nS. At 240MHz Tpd alone is 50% of your cycle interval. That
> > > translates to linear amplifier. I don't know who did your ASIC's or the
> > > system design, but 240MHz at SSTTL is going to be very hard to do.
> >
> > Thank you for your help!
> >
> > Our ASIC is committed already. We are designing the prototype
> > board to bring it up. For now, it only needs to work at
> > room temperature (instead of the worst case conditions). If
> > the IDT74ALVC16244A part (or GAL16LV8) is not fast enough for
> > room temperature application, do you know of any other part that
> > might do? We will have adjustable delay lines to tune the skew
> > among ASICs, so the skew is not the prob. But it needs
> > to drive 100 or 50 ohm transmission lines for TTL/CMOS levels.
>
>Do *not* use the GAL16LV8D (3 ns tpd). I've tried this as a 44 MHz clock
>driver on a 50-ohm line, and it doesn't work. It's a very weak driver.
>Looking at the incident wave step, it looks like about a 90-ohm output.
>Lattice's (at the time) IBIS model shows a stronger driver that can drive a
>50-ohm line just fine in simulation.
>
>-Eric
>--
>
>Eric Goodill Cisco Systems M/S SJ-N2
>mailto:[email protected] 170 W Tasman Dr
>voice: (408) 527-3460 San Jose CA 95134-1706
>fax: (408) 527-3460 (yes, the same)
>
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