On Sun, Feb 27, 2022 at 07:49 AM, Dave McGuire wrote:
As Harke said a few minutes ago, look at probe grounding. This is
often dismissed as one of those "That can't happen!" things, but it's a
very common and widely-misunderstood problem.
Always connect your probe's ground as close to the monitored circuit
node as possible, and keep the probe's ground wire as short as possible.
Jinxie,
Your spikes do sound a lot like what you'd see from excessive probing inductance caused by a large loop area from the ground lead. One simple test I often do to determine whether my probing is creating high-frequency content in the measured signal is to manually decrease the loop area by pushing the ground lead wire up against the oscilloscope probe body (basically, you want to minimize the area created by the main part of the probe and ground lead). If this decreases the amplitude of the spikes, that's a good indication that the high-frequency content is a result of poor probing and not a signal present in the DUT.
Matt
