[time-nuts] Ugly Frequency Dividers

Tim Shoppa shoppa at trailing-edge.com
Wed Aug 9 05:27:51 EDT 2006


Normand Martel <martelno at yahoo.com> wrote:
> It was part of a Marconi (damn, i don't remember the
> model number, but it was an OOOOOLD model), more
> precisely the 600 MHz divide by ten prescaler.
>
> The input divider was based on two tunnel diodes that
> acted as a div. by two divider followed by the really
> most bizarre divide by five unit i ever saw: Fifteen
> discrete NPN transistors arranged in a star (or
> pentagon (Helloooo Echelon!! ) ) topology with the
> input placed at the center of the star. The 15
> transistor were in a symmetrical loop of 5 three
> transistor units working in a closed loop.
>
> Years later, i've made searches to find the schematic
> of this prescaler, but without the model number, this
> is quasi-impossible.
>
> If one of this forum's members has this schematic, i
> would be pleased to ask for a copy!

I would make a very straightforward guess that the pentagon was
simply a divide-by-five ring counter. Each shift register is
two transistors... third transistor might be for clock buffering, or maybe
(would require a slight break in symmetry) initialization to a
known state?

Too many people seem to neglect the ring counter and go straight
to binary counters. Not sure if this is a defect of the educational
materials replicated throughout the decades or what. The ring
counter is not a one-trick-pony, instead it solves (AUTOMATICALLY)
all the glitches encountered with decoding states from binary counters.

Tim.



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