Hmm. My recollection from high school physics was that the speed of propagation along a wave guide was around 90% the speed of light - presumably limited by the dielectric. Signals along a plain old wire, on the other hand, were more like 1/3 the speed of light. Now I'm going to have to double-check that for the first time in over 40 years!
On Sunday, December 27, 2020 at 2:20:06 PM UTC-5 Chuck wrote: > 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? >> >> -- >> You received this message because you are subscribed to the Google Groups >> "neonixie-l" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/1bbc978e-4883-4b0e-920f-d5f3ff4c4c2cn%40googlegroups.com >> >> <https://groups.google.com/d/msgid/neonixie-l/1bbc978e-4883-4b0e-920f-d5f3ff4c4c2cn%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/bbe8ae0a-bb3c-4f4a-98f6-9f56bc1e1805n%40googlegroups.com > > <https://groups.google.com/d/msgid/neonixie-l/bbe8ae0a-bb3c-4f4a-98f6-9f56bc1e1805n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/480dcaf7-ce2b-45be-b8cc-bb1ee79bc5a2n%40googlegroups.com.
