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 <e...@telight.com> 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 > > > ______________________________**_________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.