Cinematronics vector generator...

Hi everybody.

I was playing with the Cinematronics vector generator last night in
Electronics Workbench (a spice simulator).

I have a couple questions that maybe someone knows the answers to.
Otherwise I'm going to try to measure it with a DSO over the weekend...
;-)

 From playing with my (fairly) realistic model, it looks like the time
for the output to react to a change in voltage at the DAC is about 1us.
Does this sound realistic? Seemed kinda fast to me. (I think this is
while in "DRAW" mode-- voltage going through the 10K+5Kpot series
current limiter. Maybe I screwed up and had it in "INIT" mode... Hmmm.)

Do any of you know what the "clipping" (z blank) timing is? For
example-- when watching the output on the "virtual scope" in Electronics
Workbench it looks like the linear portion of each charging curve starts
about 50ns after the new voltage is applied. From there it's pretty
linear out to about 150ns or so. Is z-blanking software controlled?
Seems like 50ns is pretty tight timing to keep, but since it's also the
period of the 20MHz clock it seemed like a strange number to show up
"accidentally". (I'm wondering if the clipping is done in hardware and
starts automatically one clock tick after the DAC is loaded and lasts
for two clock ticks after it.)

Anyway, it just seemed really fast, so I'm hoping for a reality check.
(This might be explained if I had the thing running with the "INIT"
switch closed instead of "DRAW"... Up too late-- don't remember.)

I also put in that weird-ass bridge rectifier-resistor *thing* in the
feedback loop of the output Op-amp. It looks like it kinda flattens out
the charge curve of the cap, but it also looked like it was screwing up
the discharge curve shape. Maybe I had it wired wrong (or it confused
SPICE, which really shouldn't happen)...

-Clay

Clayton N. Cowgill Engineering Manager
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Received on Fri Apr 3 09:19:06 1998