---
Yeah, that's a good idea. With the spec's for the LED's Vf all over
the place and its tempco causing that Vf to drift, it's going to be
really likely that it's going to fit in just right between the
logic's Voh an Vol. Oh, well, though, you've got it covered with
that: "or something."
Given a cmos fpga running at 3.3 volts Vccio, the unloaded logic will
swing to microvolts of either rail. Do you really think that a visible
led couldn't be used to reliably bias the other side of the opamps, to
anywhere between, say, 0.1 and 3.2 volts? Why would tempco matter?
You are letting your emotions shut down your ability to think, just
because you need to find fault with everything I say. That's very bad
engineering.
---
---
If you're getting annoyed, then this _is_ real life.
Checking our stock records, it looks like LM358 (daul opamp) and LM393
(comparator) both cost us about 15 cents, duals in SO-8. Our placement
and inspection costs are high, so eliminating the pullups would be a
good deal for us. But we don't worry much about pennies of parts cost;
usually there's a bigger picture.
We seldom buy quads, because duals take up about the same space but
are a lot more flexible. The op wanted 6 channels, I think.
---
Certainly not, but that's not what I was talking about. What I
_was_ talking about was that since you said "we" in reference to the
design, then you must have been a part of it, which is in conflict
with your statement: "I didn't design this particular level
shifter,"
Of course I'm part of it. I work with all my engineers, and we
brainstorm circuits all the time... every day in fact; it's a sport,
actually. I think the fast opamp level shifter, and the overall pulser
architecture, came out of such a session, and I can't remember whose
idea it was. In a proper brainstorm session, you never really know,
and you don't keep score: the ideas are enough. I certainly didn't do
the detailed circuit design on this one... I let other people have
fun, too.
John
