[time-nuts] Input filter for data logger

[Mark Sims]

Here are Wenzel's input circuits:
http://www.wenzel.com/documents/waveform.html

The TAPR TICC uses a slightly modified version of the two transistor circuit.

Also check out the LPRO-101 manual for their versions of the single CMOS gate squarer.  One thing they do is add an RC filter to the CMOS gate power supply.  

I use this version (with a 74HC86 as the input gate) on my HP-531xx time interval calibrator circuit.  Wenzel says an HC gate works  better than AC logic if you don't need to handle higher freqs.  It provides surprisingly good performance for such a simple circuit.