[time-nuts] FTS 1050A

[Bruce Griffiths]

Max Robinson wrote:
> If you use a D flip flop as a mixer it will produce the difference 
> only. You have to get the D and clock signals right I forget which one 
> has to be the highest frequency to make that work.
>
> Regards.
>
> Max.  K 4 O D S.
>
Why?
A D flipflop works well as a mixer when either the D input frequency is 
higher than the clock frequency or vice versa.
A shift register makes a better mixer in that the probability of a 
metastable state occurring at the shift register output is much smaller 
than when a single flipflop (from the same logic family) is used.
For example clocking a 74HC164 at 5.000055MHz whilst driving its serial 
data input at 5MHz produces a 55Hz beat note output albeit with jitter 
of several 5.00055MHz clock periods.

Bruce