A handy way I use, to remember the approximate speed of light, which is
also the approximate
speed at which an electrical signal travels in a wire is just to think
of it
as 1 nanosecond per foot. Approximately.
---- Original Message ----
From: "gregebert" <[email protected]>
Sent: 12/27/2020 12:32:41 AM
To: "neonixie-l" <[email protected]>
Subject: Re: [neonixie-l] How close together do a controller and
crystal need to be?
I'm assuming you are routing the output signal of an oscillator, not
the crystal signals themselves.
The rise- & fall-times of the clock signal will determine how long the
trace can be without termination. Faster edge-rates, say in the 2-3nsec range,
will limit your trace to around 1 inch.
Signals propagate around 150psec/inch, and if the rise/fall times are
about 10x (or larger) longer than the flight-time, then reflections should not
have sufficient amplitude to cause false clocking.
In the example above, 1 inch of trace has a round-trip flight-time of
300psec. If the rise and fall delays are 3nsec or larger, you can safely use 1
inch of trace without using termination networks or controlled-impedance traces.
SPICE simulations are very helpful when deciding how to design clock
lines when you cant satisfy the above rule.
On Saturday, December 26, 2020 at 4:06:26 PM UTC-8 Bill van
Dijk wrote:
As long as there is not something very
noisy on the other side of the board you’ll be just fine.
Bill
From: [email protected]
[mailto:[email protected]] On Behalf Of Erick Anderson
Sent: Saturday, December 26, 2020 6:53
PM
To: neonixie-l
<[email protected]>
Subject: [neonixie-l] How close
together do a controller and crystal need to be?
I designed a board for the 6-digit All
Spectrum controller, which uses the Dallas TCXO chip. That's what goes in the
DIP-14 socket in the picture. Right now they're as close to each other as
possible. I'm thinking about redesigning the board to be a bit shorter, and
moving the socket into the empty space at the right of the board would help.
This would make the clock signal trace much longer, but is that actually a
problem?
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