i'm new to pcb design and i'm wondering that starting from which frequency range we need to apply the high speed PCB design rules and techniques ?
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\$\begingroup\$ This pretty much a duplicate of electronics.stackexchange.com/questions/236415/… \$\endgroup\$le_top– le_top2016-06-11 13:21:48 +00:00Commented Jun 11, 2016 at 13:21
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A fairly simple and useful rule of thumb: -
Problems will start to manifest when the track length gets longer than about one tenth of the wavelength of the useful harmonic content of the signal being routed.
This is to avoid reflections affecting digital transmission of data and clocks i.e. to avoid data corruptions.
More or less the same for analogue but you can probably get a bit longer on tracks in some circumstances. All this is governed by this: -
A track that is a quarter wave long feeding an open circuit or high impedance load will look broadly like a short circuit at the sending end at that frequency.
This is the primary concern so try and understand this first. Look up quarter wave impedance transformers for additional reading.
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1\$\begingroup\$ Note that Andy talks about "usefull harmonic content", NOT about frequency, as many poeple often seem to assume. For digital signals, this more or less boils down to the raise and fall times. Even a 1 Hz signal can get you into trouble when the edges are sharp and what happens at the edges is important to you. (for instance for a clock line) \$\endgroup\$Wouter van Ooijen– Wouter van Ooijen2016-06-11 11:41:13 +00:00Commented Jun 11, 2016 at 11:41
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\$\begingroup\$ In addiition to Andy's answer, sometimes (for logic devices) some guidance may be found from the IBIS model (most modern parts have these available). Look for the ramp definition within the file. \$\endgroup\$Peter Smith– Peter Smith2016-06-11 14:00:09 +00:00Commented Jun 11, 2016 at 14:00
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\$\begingroup\$ The wavelength on the PCB is not determined by the (full) vacuum speed of light but only the speed for electric waves on that PCB. Instead of 0.3 m per nanosecond only about 0.2 m per ns. \$\endgroup\$Uwe– Uwe2016-06-13 14:56:48 +00:00Commented Jun 13, 2016 at 14:56