I have designed a GPS disciplined oscillator.

It's performance is nominal for the design, but the question I presently have is about conditioning the output for presentation to a front panel BNC jack.

At the moment, I have an NB3N551 1-4 fan-out buffer. 1 output of that clocks the controller and the other 3 go through 33 ohm resistors (the output is nominally 20 ohms impedance) to a 6 pin DIP header.

I've used this in a couple ways... I've viewed the output with a 10x scope probe (1M-ohm impedance on the scope input), and I've fed it to another circuit of mine with an AC coupled 50 ohm thevenin termination feeding a schmitt trigger buffer. Those work just fine.

What's not so great is if I look at the output on my scope with a 1x probe. It's not terribly square anymore. I haven't yet tried T-ing a 50 ohm terminator yet, but plan on it later on today (perhaps therefore this question is premature).

Is there a standard output/distribution circuit I should be using instead of or in addition to the NB3N551?

Keep in mind that while I don't really care about propagation delay in this application (as long as it's constant), adding tons of jitter would not be great.

  • \$\begingroup\$ Is there an intended receiver for this signal? Or what types of receivers will you support? \$\endgroup\$
    – Justin
    Commented Sep 2, 2015 at 18:17
  • \$\begingroup\$ This is intended to potentially feed lab equipment that has a reference clock input, but in general the desire is for it to be maximally useful without any degradation in the stability. \$\endgroup\$
    – nsayer
    Commented Sep 2, 2015 at 18:25

1 Answer 1


Turns out this was a red herring. When I finally got around to looking at it on a proper 50 ohm terminated scope with 50 ohm coax, the signal looks fine. It's around 1.5v from low to high and 10-90% rise and fall times are around 5 ns.


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