[time-nuts] Re: [tacgps] IC for Clock Input?

John Kolb jlkolb at cts.com
Mon Sep 6 23:53:19 EDT 2004

On Mon, 6 Sep 2004, Brooke Clarke wrote:

> I'm trying again to make a clock that will use the output from a
> precision frequency standard (1, 5 or 10 MHz) as it's heartbeat.
> At first I was going to use the 74HCT4046, like was done by Brooks
> Shera, but I've discovered that the through hole version of this part is
> out of production.  Brooks' has them in stock to support his board, but
> I would like to find a new part.
> In my case all the input IC needs to do is convert the input RF sine
> wave into a clean TTL drive for the microprocessor.
> Can I just use a Schmitt gate like the 74HCT14N?  To center the A.C.
> coupled input a 68 Ohm resistor to ground and a 200 Ohm resistor to +5
> Volts will bias the gate to the center of it's hysteresis and any
> excursion greater than about 1 Volts (about 20 mw) will cause it to
> switch.

That should work as long as you have a low impedance source
driving it. I would probably use a fast op-amp, however, to
insure there's enough gain to square up the sine wave well.
One of the op-amps that runs on a +5V supply only, and let
it bang into the stops.


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