[time-nuts] Zero-Crossing Detector Design?

[Michael Tharp]

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