Author Topic: Long low speed traces signal integrity  (Read 2264 times)

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Offline newtekuserTopic starter

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Long low speed traces signal integrity
« on: December 23, 2024, 07:14:01 pm »
My 16x2 LCD is connected to the MCU using pretty long traces with the longest being 4cm. To mitigate SI issues I am using a ground pour connected to the adjacent GND plane underneath using stitching vias spaced about 1cm apart on the perimeter and along the traces.
Do I even need to be concerned about this considering that when I had the LCD connected using a much longer ribbon cable, I did not encounter any issues? Being a noob at this technique I'm worried that I'm going to introduce parasitic inductance with the big pour.

Attached is my layout.

 

Online thm_w

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Re: Long low speed traces signal integrity
« Reply #1 on: December 23, 2024, 10:15:01 pm »
Do you need to be concerned? No.
But this is still a good layout, good practice, so why not.

The plane will add parasitic capacitance not inductance, which won't be an issue at the low speeds the LCD is driven at.
It will also shield the noise from transferring between traces (since you put space between them).

https://www.protoexpress.com/blog/how-to-reduce-parasitic-capacitance-pcb-layout/
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Offline newtekuserTopic starter

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Re: Long low speed traces signal integrity
« Reply #2 on: December 23, 2024, 11:19:32 pm »
Do you need to be concerned? No.
But this is still a good layout, good practice, so why not.

The plane will add parasitic capacitance not inductance, which won't be an issue at the low speeds the LCD is driven at.
It will also shield the noise from transferring between traces (since you put space between them).

https://www.protoexpress.com/blog/how-to-reduce-parasitic-capacitance-pcb-layout/

Thank you! Meant to say capacitance and wrote inductance  |O
 

Online Smokey

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Re: Long low speed traces signal integrity
« Reply #3 on: December 23, 2024, 11:41:09 pm »
properly designed ribbon cables will alternate important signals with grounds, which is about the best you can do when sending multiple signals on a cable.
« Last Edit: December 24, 2024, 11:07:11 am by Smokey »
 

Offline David Hess

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Re: Long low speed traces signal integrity
« Reply #4 on: December 24, 2024, 10:08:59 am »
It will reduce the inductance and increase the capacitance, lowering the impedance of the traces.  If the circuit was sensitive to impedance then this could matter, but when driving an LCD?

Power consumption driving the higher capacitance lower impedance lines will be higher because more charge is being moved around.  In a micropower application this could matter, but then the ground plane would be relieved as well.
 


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