[time-nuts] DMTD - analog multiplier vs. diode mixer ?

Attila Kinali attila at kinali.ch
Sun Jan 10 10:21:23 UTC 2016

God morgon,

On Sat, 9 Jan 2016 23:01:31 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> > A D-Flipflop is a rather weird mixer. I have not done the calculation,
> > but i'm pretty sure that the output is not exactly what you'd expect
> > it from a normal mixer (namely having half the energy at the frequeny
> > difference and half at the sum).
> It's not that wierd. It's a sampler, and thus it acts like a mixer as if 
> the signal is spikes, which is just another interpretation of the 
> Nyquist frequency aliasing. Meta-stability however creates an 
> "interesting" aspect.

Ah right! That also explains my uneasy feeling about it :-)

It's relatively easy to get around metastabilitiy: just add another
couple of D-flipflops in series. Unfortunately, that will only fix
the metastable lingering in-between. It wont fix the edge being at
the wrong time.

> A third digital phase-detector is the SR flip-flop. It avoids the 180 
> degree phase property (really a triangle wave signal) of the XOR, but 
> give a 360 degree phase sawtooth. This can be helpful in certain lock-up 
> conditions.

SR-flipflop? Are you refering to the JK-FF phase detector or the PFD?

> The phase-frequency detector of the 4046 and the like has additional 
> flip-flops to remember slipped cycles and forcing the frequency to 
> regain that. Those provide a strong frequency lock mechanism with a 
> phase detector in one.

Interesting... i have to look into the old datasheets.

> > Single gate chips better than multi gate chips.
> > (no interference through the power supply of the different sub-parts)
> Well, you should wire the other parts into passive mode.

That would be a waste of good PCB space ;-)

				Attila Kinali

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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