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Chef Jeff , 07-11-2024, 03:21 AM

Hello PCBers,

Video: https://www.youtube.com/watch?v=vALt6Sd9vlY ```
Time stamp: 40:47, slide 26 says "NOT Necessary to Split Ground above 20kHz!"

What is happening below 20kHz that would require you or be a very good idea
for you to split ground planes? I missed it in the video and I can't seem to find the time stamp on it where he explains exactly why.

Thank you!
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Chef Jeff , 07-11-2024, 04:05 AM

wait is it becasue the current would travel through the ground planes on all layers so it would be better to isolate the ground in this case so the current only travels on one gnd layer? Is that the argument?

QDrives , 07-11-2024, 07:44 PM

Rick Hartley talks about ultra sensitive circuits (uV). He also states that is the circuits are separated enough (>= 20H) it does not give a problem, even for those circuits.

User , 07-11-2024, 08:15 PM

I am curious to know what exactly happens when return current from sensitive analog and digital cross each other, how exactly do they interfere with each other?

QDrives , 07-11-2024, 08:21 PM

Sensitive analog cannot interfere with digital -- that is like your hand interfering a wall when you kill a mosquito.
Digital or high power analog can interfere with sensitive analog. Like Rick mentioned, your ADC may give incorrect (spurious) results.

Chef Jeff , 07-12-2024, 01:31 AM

I get all that but what I am more concerned with is the bullet point that states “not necessary to split grounds above 20kHz”. You are saying he said this bullet point is basically wrong in the video? I am sorta suspicious with how you answered my question lol.

QDrives , 07-12-2024, 10:15 PM

The lower the frequency, the 'wider' the return path.
As often shown, return currents do not flow in a direct line from load to source. However, that is at 'higher' frequencies. Not so for DC. So at frequencies below 20kHz, you may get return currents flowing in the ground return path of your sensitive analog circuit.
However, if you look here: https://youtu.be/nPx2iqmVAHY?t=90 you see current flowing all over the board. That is at 1MHz. How much of it is also design/layout...???

Chef Jeff , 07-12-2024, 11:49 PM

Yup I get it now. Thank you for taking the time to follow up on this post.