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

Richard (Rick) Karlquist richard at karlquist.com
Sun Jan 10 18:53:57 UTC 2016

Phase frequency detectors (starting with the legendary MC4044)
being made out of flip flops, had metastability and/or race
conditions.  Motorola showed a block diagram made of gates,
as if it were combinatorial logic, but because of the feedback,
it is actually a state machine, as described in the MC4044
data sheet.  It had a dead zone around zero phase that came
to light when Fairchild introduced the competing 11C44 PFD
using Eric Breeze's patent to fix the dead zone.  The
11C44 data sheet showed their dead zone, vs Brand M.
Even that improved chip still had a "funny" zone, it just
never went to zero gain.

Fast forward to today, we are now seeing PFD's made
with samplers.  They too have a bunch of issues with
phase noise floors.  None of them come close to a mixer.

In the 5071A, I used a mixer as a phase detector that
had some flip flops only used for acquisition, so they
were non players in terms of phase noise.  I still think
I would do that even if I had to do over 25 years later.

Rick Karlquist N6RK

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