CMOS/TTL chip questions (was: Cmos Latch Octal)

[Arthur Harrison]

-----Original Message-----
From: Haible Juergen <Juergen.Haible at nbgm.siemens.de>
To: DIY <synth-diy at mailhost.bpa.nl>; Arthur Harrison
<theremin1 at worldnet.att.net>
Date: Friday, November 20, 1998 3:41 AM
Subject: AW: CMOS/TTL chip questions (was: Cmos Latch Octal)


> >The ideal part for an oscillator, in any case, is
> >the easily-obtained CD4069UBE.

>Yes, that's the one that always comes unbuffered, and it's great
>when you need a linear operating point (crystal oscillator with
>smooth rather than steep slope rectangle output, for example).

>For simple RC oscillators, my fav is a single schmitt trigger inverter
>(40106, I think), with RC lowpass feedback. Can't beat that in terms
>of efficiency, one gate, one resistor, one capacitor.
>When I have two ordinary
>gates left from the rest of the design, I build the 2-gate / 2-resistor /
>1-capacitor oscillator you described. Never ran into problems
>so far (with "B" type chips), but then again I have not built more
>than a handful of these oscillators yet.

Agreed, the 40106 hex-inverter Schmitt is a great osc., and if you use the
4093
quad-nand Schmitt, it's keyable via the extra input, too.  The minor
drawback
to these is a somewhat greater variation of F vs. PS voltage, and also a
larger
part-to-part F variation.  However, the output transitions are superbly
clean,
and never cause mis-triggering.

I wish they made the other flavor gates as Schmitts,
e.g., 4071, 4081, etc.  I asked Harris about this, but they weren't the
LEAST
bit interested.  (Maybe when T.I. buys the line, I'll ask them.)

Manufacturers aren't interested in these jelly-bean parts any more; anything
that isn't a giant "one chip" solution isn't profitable or glamorous enough
for
the stockholders.  I'm always amazed at how well op-amps have been doing,
despite this.

> >Buffered [B] CMOS devices are types in which the output "on"
>impedance
> >is independent of any and all valid input logic conditions, both
>preceding
> >and present.  All such CMOS product are designated by the suffix
>"B"
> >following the basic type number."

>I wouldn't dare to say that's wrong (in fact I don't know), but I would
>have expected exactly the contrary ! I thought "B" gates are more
>or less the same as "A" gates for the logical part, but with some
>extra inverters at the output. This should make the gain higher, the
>output slope steeper, and should provide *more*, not less, decoupling
>from the input voltages that "A" devices.

Yes, all that is true, I believe.  I don't think the RCA text is too
much to the contrary.

>At least for simple gates
>like 4001. Again, it seems you have done more research than I,
>but I feel puzzled because it's so against "common sense".

I spent hours looking at all the various RCA texts on these devices.
(They are my favorite logic for mixed-mode circuits; you can do
the linear stuff _and_ the CMOS at +/-6v).  The texts are full of
surprises, often not intuitive at all!

-Art