Especially as the inverting gates have independent source and/or drain
connections - series resistors can be used to lower even more the
consumption when biased in the linear region...
On 6/28/2013 7:20 AM, Don Latham wrote:
Maybe the old 4007 cmos would be better...
Don
paul swed
Yes it makes a very fine 35 Mhz oscillator and reasonably stable.
Been there and done that.
Hey the systems done. May remod it one day but bigger fish to fry with
the
d-psk-r
Regards
Paul
WB8TSL
On Thu, Jun 27, 2013 at 6:41 PM, David McGaw
<[email protected]>wrote:
Lower gain is better as long as it oscillates. The 74HCU04 is
unlikely to
drive spurious responses. The 74HC04 is OK as long as you keep the
feedback gain low - sometimes a series resistor from the output to the
resonant circuit is required. A 74HC14 is the WRONG part for the job
as it
can and will oscillate without the crystal controlling it - just try
it
with a resistor for feedback and a capacitor to ground at the input,
no
crystal.
David N1HAC
On 6/27/13 6:30 PM, paul swed wrote:
I will say the fact is the 74hc14 is a bit of a power pig we are
talking
12
ma. The rcvr is something much less like 100 ua. At least for the
moment
it
all works but 12 ma is a pig.
Especially when you take the signal out and knock it down to 100-200
uv.
Regards
Paul.
On Thu, Jun 27, 2013 at 5:37 PM, ed breya<[email protected]> wrote:
Still having email problems - here we go again. This is second try,
please
excuse if both show up.
Hal Murray said:
They make 74xU04 for many values of x. The U is for Unbuffered.
They
have
lower gain in the linear region.
I thought they were intended to be used for things like this, but I
don't
understand that area. Can anybody give me a quick lesson or point
me at
a
good URL?<
I always thought the unbuffered "U" versions were preferred for ring
oscillators mostly to save power - you don't want the high-drive
output
stages to be cooking away in linear mode if not needed. The
propagation
delay can also be less since the U ones have only one stage instead
of
three (the building block is the totem-pole inverter stage), but
they
can't
drive very much load anyway. I think that most MSI and LSI parts
that
have
built-in ring/crystal oscillator sections use the U topology, but I
don't
think there's anything special about it - it's the simplest thing
that
works.
I've made quite a few CD4000 and 74HC oscillators, and never worried
too
much about U versions or not, except for battery-run items where
power is
critical (or you can run the oscillator at lower voltage). Often
they are
made from inverting gates that are part of a shared package, where
you
wouldn't want puny drive capability in the other gates anyway. They
are
relative power hogs though, whenever linear biasing is needed.
Except in
the 4000 series, I don't know if U versions are available in
anything but
the '04 hex inverter, but I suppose it's possible. I think the
Schmitt-trigger types like HC14 are necessarily buffered, so have
three
stages, since you need a non-inverted version of the signal for the
positive feedback to the input.
I've never tried making one in 74AC - I don't know if it's even
possible
to bias one up that way without it burning up. I'm working on some
related
circuits now, so maybe I'll set up an experiment to see how much
current
it
would take for one inverter - I've often wondered about this.
I read about this years ago in various CMOS application notes, so I
may
be
missing some key points - there should be plenty of info online. The
older
generation (when CMOS was fairly new) info may provide more detail
about
the guts than that related to the newer, higher performance
families.
Ed
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