Figure 1: Teledyne LeCroy's ZS2500
Ideally, an oscilloscope probe would make contact with the circuit under test and transmit its signal from the tip of the probe to the instrument's input with perfect fidelity. We would like to see the probe exhibit zero attenuation, infinite bandwidth, and linear phase characteristics at all frequencies.
The circuit under test has its particular electrical characteristics for a given signal, which are what we want to measure. Alas, the probe itself is a circuit with its own electrical characteristics. When the probe tip meets the circuit under test, their characteristics combine in a way that can affect the measurement results. The probe's input impedance will be introduced into the circuit. All probes present some amount of resistive, capacitive, and inductive loading that must be accounted for.
|Figure 2: Probe input equivalent circuit|
How can ground lead corruption be alleviated? One way is to raise the resonant frequency of the LC network by decreasing the inductance, the capacitance, or both. Realistically, because the input capacitance is already very low, the only option is to reduce the input inductance. This is achieved by using input and ground leads that are as short as possible.
Capacitive loading can be a difficult nut to crack, as it can affect rise-time, bandwidth, and delay measurements. At high frequencies, capacitive loading can affect the amplitude and waveshape of measured signals.