[time-nuts] crunching numbers from XOR phase detector

Chris Albertson albertson.chris at gmail.com
Wed Jan 4 17:21:06 UTC 2012


On Wed, Jan 4, 2012 at 12:58 AM, Hal Murray <hmurray at megapathdsl.net> wrote:

>
> Neat.  Thanks for sharing.
>
> With a XOR, you can't tell which input is higher frequency.  I think you
> can
> fix that with a second XOR and a delay line.


I think you can build a PFD or Phase Frequency Detector with three or four
flip flops.  This avoid using the delay line and works over a wide range.

If I'm not mistaken there is a PFD inside the 74HC4046.   It uses flip
flops.  Be sure to look at the 74HC type not the cd4046.   The 75hc type
works up to 18MHz.


Chris Albertson
Redondo Beach, California


More information about the time-nuts mailing list