[time-nuts] DMTD mixer question

[Bruce Griffiths]

pablo alvarez wrote:
> Hi,
>
> I have been looking at several Dual Mixer Time Difference designs. As
> far as I know the basic architecture is based on generating a tone
> with an small frequency offset respect to the nominal clocks
> frequency, analogue mixing of the clocks, low pass filtering, then a
> slow zero crossing detector and finally a time interval counter or
> time stamp unit.
>
> I have this naïf question: would not it be better and simpler to use
> directly an ECL D flip-flop as a mixer instead of an analogue one? I
> suppose analogue mixers are preferred because they provide with a
> better "differential tempco", but using ECL logic can provide also
> with a good tempco.
>
> What is your experience?
>
>
> Cheers
>
> Pablo
>
>   
Pablo

Flipflop mixers tend to produce glitches at the beat frequency transitions.
A digital PFD in a PLL doesnt produce a beat frequency output when
locked so such glitches arent a problem,

Bruce