[time-nuts] Sub Pico Second Phase logger

[Bruce Griffiths]

> Warren
>
> Another potential issue is crosstalk between flipflops in the same
> package, in particular between the 2 clock signals.
> Such effects will not be evident when using a single clock source to
> evaluate the system noise.
> Using fully differential logic such as ECL will reduce such coupling at
> the expense on increased power dissipation and relatively high logic
> level tempcos.
> Dithering one or both of the clocks may help.
>
> Bruce
>
>   
The effect of cross coupling between the clocks will be more significant
as the phase shift between the clocks approaches 0 or 180 degrees (for
50% duty cycle clocks).
Dividing the input frequencies by 4 to produce quadrature phase outputs
wont help.
You would need to actually use a pair of phase shifted clocks from one
of the input sources feeding separate dividers so that clock transitions
of the 2 clocks within a chip do not coincide.
Either a selected length of coax or a quadrature hybrid would suffice
for producing the 2 clocks with a near 90 degree phase shift.

Bruce