Re: gEDA-user: opamp slew rate limiting

[gene glick <carzrgr8@xxxxxxxxxxxxx>]

Mark Rages wrote:
> 
> I thought the whole point
> of a Schmitt input was to give the input a little "snap" and therefore
> increase the rise/fall times. 
It will.

In my setup, 2 channels each setup as I described.  The relative phase 
from one channel to the other remained pretty much constant throughout 
the various stages (which I require), including the slow-edge opamp 
circuit.  It all fell apart going through the schmitt trigger. The 
faster edge into the schmitt trigger eliminated the phase/timing 
distortion.  All in all, and I think most people agree, this isn't the 
ideal circuit for the given application :)  I don't even want to 
describe the lousy asynchronous flip-flop design that follows the 
schmitt trigger for fear of a scolding :)  (not my design, I have to 
repeat that for my sanity)


  In fact, I've done something similar to
> what you're doing.  IIRC, it was like this: digital signal -> big long
> RC -> schmitt inverter -> 4000-series flip-flop clock.   And that
> circuit, inelegant as it was, worked fine.
yep.  You need the fast-ish edge for the clock.  The CD4000 logic don't 
require very fast edges (5uS rise, for example) to work. Anything slower 
and you cannot guarantee the timing specs.  That's what the scmitt 
trigger did in your case.


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