[sdiy] linear schottky TTL operation

[harrybissell]

Another problem might be the bias current... I bet it would fry if
you used it linear...  Maybe if you use only ONE gate and limit the supply
current.

H^) harry

"Roy J. Tellason" wrote:

> On Saturday 18 June 2005 11:50 am, anthony wrote:
> > Is it possible to use schottky based TTL gates in the linear mode? I
> > figured since the transistors don't saturate that they could. I guess a
> > better point to ponder is would there ever be a reason to want to? I was
> > thinking about using the 74LS121 that I have for a pulse/ramp generator but
> > I wouldn't need to run this in linear mode to do that at all. Using dual
> > monostables seems like a cool way to do this too. I was also thinking about
> > the 74LS06 and 74LS19 - used as oscillators they wouldn't need to be run in
> > linear mode either (well definitely with the '06 but I suppose its having
> > open collectors makes it special). And that led me to wonder about using
> > NAND gates or inverters in something like the Wasp filter?
> >
> > Having bucketloads of old TTL gates makes you think about stuff you
> > wouldn't normally think about.
>
> Schottky-based stuff ain't *old*,  7400 (without the "LS" in the middle of the
> number),  now _that's_ old...   :-)
>
> > And heck what have I got to lose? I don't care if I blow out a few chips. I
> > think I'll whip something together that I think /shouldn't/ work in both
> > schottky and non (I think I have some ceramic '04s). I'll check it out on
> > the 'scope. Sometimes I wonder if I spend too much time thinking about
> > things this way... but nah...
>
> Do you have a copy of Don Lanaster's TTL Cookbook?  It'd probably be worth
> your while to get one if not,  as he gets into that stuff somewhat.
>
> I've done very little experimenting along these lines.  I can say that the
> circuit given as some typical astable using a single schmitt inverter (or
> gate) didn't work right off when I tried it with TTL instead of the CMOS I
> was looking at in the schematic -- the impedances were all wrong,  and I had
> to go to a *way* lower value of resistor with correspondingly bigger value of
> capacitor to get the same effect.
>
> TTL also generates noise spikes,  trying to run it in any sort of linear mode
> is gonna be worse in this respect.