8 ms·
Huh, article says not to worry about traces unless dealing with 100 MHz+ signal lines. Isn't that very common? Hell even the MSP430 is running at 25 MHz these
by krapht 7y ago
Huh, article says not to worry about traces unless dealing with 100 MHz+ signal lines.
Isn't that very common? Hell even the MSP430 is running at 25 MHz these days.
And for all the other reasons listed in the article, you should avoid sharp corners. It's lazy to do otherwise when mitred 45 degree bends or curves are so easy to generate in a CAD tool. It's the hardware version of a code smell - the board house (compiler) might not care, but it should be fixed - don't give up freely obtained manufacturing slack because you couldn't set up a trace bend rule.
I kind of feel like PCB layout ought to just be done by the antenna engineers for any serious product with wireless comms or high speed I/O.
- IshKebab 7y ago100 MHz in traces is very uncommon for typical DIY PCBs. The only place I can think you'd get that is in a microcontroller clock, but most people use modules or internal clocks.
- yetihehe 7y agoOr a 8mhz crystal and PLL in mcu.
- philpem 7y agoIt's not just the fundamental frequency that matters -- a square wave with fast edges will have harmonics which lead off to a surprisingly high frequency. Even on fairly slow signals they can be into the tens or hundreds of MHz.
- nitrogen 7y agoOr USB 2.0 if you are using a USB-capable microcontroller.
- IshKebab 7y agoUSB 2 High Speed support is still rare in microcontrollers. Most still only support Full Speed which is only 12 Mb/s. (If anyone is looking for this btw the best option I found is Atmel's SAM ARM microcontrollers, e.g. as used in the Arduino Due.)
- TickleSteve 7y agoOn microcontrollers nothing external to the processor is running at that sort of rate. Even the clock is typically multiplied up many times so you won't tend to see >100MHz lines. QSPI Flashes typically have ~50MHz line which is quite common, but not much else.
- crispyambulance 7y agoOK, but it's not just the clock rate that enters into the decision, one must also consider the rise-time of the edges. If you're using, for example, a fast logic family like LVC, fast edges on badly routed traces can radiate and interfere with other parts of the circuit, even if you're dealing with "low" clock rates or simple un-clocked logic.
- Junk_Collector 7y agoYes, the rule of thumb for low frequency square wave clocks (a few GHz or less) is that your trace, routing, and connectors should all support up to the 5th harmonic, or 5 times the clock frequency. At higher frequencies the 5th harmonic is to high to realistically achieve, and you start to see reliance on sine wave clocks or heavy use of equalization to remove clock distortion from the trace. This applies for digital buses as well. If anyone is curious about how traces impact data throughput, I highly recommend they look up eye diagrams.