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I have a circuit in that GPIO_1 (yellow trace) is generating repeating signals to control an NMOS and GPIO_2 (green trace) is controlling an LED driver (buck DC/DC) load via an NMOS switch.

When a occasion that if GPIO_1 is pull-high (or low) at the same time when GPIO_2 is outputting signal, GPIO_1's voltage will slightly increase by 500 mV or so and then drops back when GPIO_2 is not output signal.

Both the load and the MCU are supplied by the same power source though. But I do realize that the 3V3 LDO (supplies the MCU) is also having the same behavior as well. What is happening here?

enter image description here

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    \$\begingroup\$ Could be that the regulator is struggling to provide enough current, or that you have ground currents or noise passing through the ground plane. Or simply that your oscilloscope probe is poorly grounded even. Without a schematic it is all speculation. \$\endgroup\$
    – Lundin
    Commented Mar 26 at 10:12
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    \$\begingroup\$ A schematic is needed along with links to relevant data sheets. Possibly a PCB layout might be required. Details of how you probe the nodes and where you connect the oscilloscope earth point are also useful. \$\endgroup\$
    – Andy aka
    Commented Mar 26 at 10:19
  • \$\begingroup\$ @Andyaka Looks like it only happens when the ground probe of the oscilloscope connects the GND before the Common Mode Choke on the board, it disappears when the ground probe is probing GND net after the CMC. \$\endgroup\$
    – Travis Su
    Commented Mar 26 at 10:33
  • \$\begingroup\$ Well there you go then - always suspect poor probe ground. Some probes come with a mechanical part where you can attach a ground near the tip itself. Quite handy, if you can only find a good ground source near where you are measuring. \$\endgroup\$
    – Lundin
    Commented Mar 26 at 10:37
  • \$\begingroup\$ @Lundin the regulator only supplies the MCU so it should be fine. I think you might be right about the grounding of the oscilloscope probe. \$\endgroup\$
    – Travis Su
    Commented Mar 26 at 10:38

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