[time-nuts] Phase, One edge or two? (was Digital mixing with a D Flip Flop)

pablo alvarez pabloalvarezsanchez at gmail.com
Wed Nov 26 07:24:20 EST 2014

Hi Warren,

I arrive a bit late to this discussion, but I hope I can help. I guess the
reason for using only one edge is based on the fact that WR is originally
designed to measure the phase between a decoded data clock and a system
clock. The problem is that this decoded data clock is locked to the
incoming data by means of a PFD in the Spartan6/Virtex6 GTP. The PFD
normaly only looks at rising edges, so any change in the clock duty cycle
will translate in a phase change in the falling edge and not in the rising
edge. I am not sure this is really the case, but we certainly had this
discussion at the time, but I don't remember if there was any real
measurement made.



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