[sdiy] Frequecy Divisor Question (TTL pulse stretcher needed)

[The Old Crow]

  The rules for UHF/microwave circuit design probably share a lot of those 
rules.  Boards have to be laid out in a specific manner to avoid/minimize 
RF-specific problems.

  Take a look at a modern computer motherboard.  The timing between RAM, 
CPU and the chipset has gotten so tight that the boards must be generated 
by an autorouter; looking at a board you'll see all sort of "squiggled" 
traces (particularly near the RAM sockets) as the design requires the 
signals appear exactly simultaneously.  The squiggles in this case assure 
that the trace lengths are all the same for each address/dats bit, etc.  
Typically electrons travel 30cm in 1 nanosecond through a copper trace, 
and when the 'valid data widnow' is 2ns wide, traces of various lengths 
would skew the arrival times of the dozens of signals such that the valid 
window would come and go before all the lines were stable.

  Never had this problem with a 4MHz Z-80A twenty years ago... ;)


Crow
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On Sat, 1 Nov 2003, David Cornutt wrote:

> things like differential pairs of traces for clock lines.  I worked on a
> team that designed and maintained a special board router package that
> obeyed all kinds of special rules, like minimizing corners to reduce
> stray induction.  A trick that the designers used to do was to make
> inductors on the board itself by running a squiggle trace of a specified
> length and spacing.  It came out looking like a little potato masher on
> the board.