This paper mainly introduces the influence of different grounding methods of oscilloscope probe on the measurement signal. Good grounding can make the measurement more accurate.

The probe and oscilloscope constitute a test equipment with a certain input resistance and input capacitance, and the measured signal is equivalent to a source with a certain internal resistance and working load. The equivalent model of theoretical measurement is shown in the figure below:

The equivalent model of alligator clamp measurement used in actual measurement is shown in the figure below:

Because the ground wire is a wire, it has a certain number of distributed inductors. The longer the wire is, the greater the inductance is. In the conventional measurement method, the crocodile line will introduce the distributed inductance, which will interact with the probe capacitance and form resonance at a certain frequency point determined by LG and CP values, resulting in the phenomenon of amplitude reduction oscillation.

The influence of resonance point is different in frequency domain and time domain. The time domain response measured by longwire is similar to that measured by conventional (crocodile line). The longer the ground wire is, the larger the inductance will be. It will form a resonance frequency point with the capacitance of the probe, which will produce obvious overshoot and amplitude reduction oscillation on the fast edge pulse. Therefore, when measuring high-frequency signal, the shorter the probe ground wire is, the better. There are two kinds of oscilloscope grounding wires: alligator clip and grounding spring. When using alligator clip, the area of grounding loop must be minimized.

Editor in charge: GT