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Measuring ground voltage.

Hi All,

I have a embedded system that includes CPU/RAM/FLASH/UART/Wireless
Chip... etc.

When I measured the voltage of ground:

Scope's gnd point to ground A, another point ( red, should I say
postive measuring point?) point to another ground - B ( but they should
be the same voltage )

When my system is running, decoding/transmitting ...etc, I can see the
voltage of ground is abruptly changing,..., not keep in the 0V.

Does it correct? and Why? should I add more circuit to stabilize it ?

Best regards,


Jan 1, 1970
In order for digital logic to operate correctly, a properly designed
power and ground system is required.

How is the ground in your system constructed? Are you using
'serpentine' traces or are you using a solid ground plane? What do you
have for bypass capacitors?

The high speed (frequency) components of your digital siganls, due to
the rise and fall of the signals, not the clock speed, follow the path
of least inductance compared to the lower speed portions which follow
the path of least resistance. A solid ground plane is usually required
to achieve a low inductance ground system. If you used serpentine
traces you may be very surprised at the paths taken by your ground

Measuring the noise on a ground system can be trickier. You will run
into problems with the loop inductance of your probe, especailly if you
attempt to use a probe cap on a 10x probe and a flying ground lead.