[time-nuts] sine to square wave circuits - performance data?

Bob kb8tq kb8tq at n1k.org
Wed Oct 4 16:51:23 EDT 2017


Hi


> On Oct 4, 2017, at 11:21 AM, Mark Sims <holrum at hotmail.com> wrote:
> 
> Wenzel says an HC device tends to work better than an AC device in squarer applications.  

That’s not the case for broadband phase noise or for close in jitter. The issue with the older 
AC parts is the crummy lead frame pinout. Setting them up so they did not oscillate was not
as easy as it should have been. More modern single gate packages no long have those issues.

There is always an … except … If you do a “feedback resistor” bias, forget about any sort of 
fast gate. Bias it with two resistors on the input and it should be fine. If the second resistor blows
your budget then yes, it’s a issue.

Bob


> 
> My calibrator board has a place for the feedback resistor so that I can implement the second LPRO circuit (or add hysteresis to the squarer gate.
> 
> ----------------
> 
>> I find it interesting that a simple 74AC04 performs so well (given enough
> input power) compared to even an LT1016.
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