[SI-LIST] Re: output circuit for 68000 NMOS driver

Jim

The output driver uses nfets for both pull up and pull down.
Voh is not as good as using a depletion device due to the VT loss,
but it avoids the large current that a depletion pull up device
would waste when the output is low. The depletion mode devices
are used in the logic gates as a resistive pull up.

This is going way back in history, but as I remember
for 5V operation the levels looked like:

Vil 0.8V
Vih 2.0V

Voh 2.4V  (maybe at 200uA)
Voh 0.4V  (maybe at 1.6 mA)

Some signals had higher driver currents.
I hope this helps. What are you doing with NMOS devices?


Sandy Taylor
CMOS Solutions
Olga Wa



Peterson, James F (FL51) wrote:
> 
> Hello,
> 
> I have been looking for information on the drivers of an old 68000
> processor. The users manual says these outputs are NMOS technology but I
> don't have any information on the topology or circuit configuration of NMOS.
> Someone mentioned that it was "depletion mode NMOS".....
> 
> I'm looking for details of the outputs (circuit config., Voh (min, and typ),
> functional description, etc.). Anybody's help would be much appreciated.
> 
> Jim Peterson
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