[time-nuts] What is a Time-Nut grade Zero Crossing Circuit?

Rick Karlquist richard at karlquist.com
Thu Jul 31 16:13:34 EDT 2008

Two things NOT to do:

1.  Do NOT use ECL.  CMOS is much lower jitter.

2.  Do NOT use a comparator to square up the sine wave.
Especially don't use a ultrafast ECL based comparator.


Some things that you should do:

Make all circuitry differential if possible.  Make your 10 MHz
source differential by putting a transformer on the output.

Band pass filter your 10 MHz source with an LC filter.
I recommend Coilcraft Unicoils or Maxicoils.

Rick Karlquist N6RK

Bob Paddock wrote:
> Can you point me to a Time-Nut grade Zero Crossing
> circuit that I can feed a Actel Igloo FPGA (It doesn't
> like sine waves)?
> For the sake of discussion the source signal
> is a ThunderBolt at 10 MHz.
> The FPGA is rated to 350 MHz, so no need to have
> a 5.0000000000000000 GHz Zero Crossing circuit. ;-)
> The FPGA has several interface styles,
> so we are not limited to just TTL or CMOS.
> Suggestions?
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