Hi I think I'd call that a limiter rather than a zero crossing detector, that is indeed a bit picky.
I think you will have better luck with a fixed bias on the input to the first inverter rather than with the 1 meg feedback resistor. With the feedback resistor the inverter tends to self oscillate. The self biased stage tends to go to one or the other state when the input is removed. With either approach, you will get the best performance when the AC signal is almost over-driving the input. Bob On Jul 19, 2012, at 8:23 PM, Michael Tharp wrote: > On 07/19/2012 07:36 PM, Al Wolfe wrote: >> Chris, >> The simplest zero crossing detector would be to feed your 1 volt, 10 >> mHz from the XL-DC into the input of an IC with schmidt trigger inputs. >> You would need to provide a series coupling cap and probably some DC >> bias from a pot to adjust symmetry of the output. I would also think >> that if you ran the four or six inverters of a schmidt trigger inverter >> chip in series that you would get a pretty good square wave out the end. > > One circuit I was recommended when I was looking for ideas uses a 1M resistor > to feed the output of the inverter back to the input to self-bias, like this: > > http://partiallystapled.com/~gxti/circuits/2012/07/06-beanpole.png > > I'm also trying a discrete approach based on the TADD-2 / T2-mini: > > http://partiallystapled.com/~gxti/circuits/2012/07/06-tadpole.png > > The latter has definitely been used successfully in timing applications but > the simplicity of the inverter approach is very appealing, so I'm giving both > a test, along with some other miscellaneous GPSDO components, before > proceeding with a full GPSDO. > > -- m. tharp > > _______________________________________________ > 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. _______________________________________________ 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.
