The input impedance of a differential probe is a core parameter for evaluating its performance, typically equivalent to a parallel combination of a 1 MΩ resistor and several picofarad capacitors. This structure directly influences the load effect the probe imposes on the circuit under test.

In DC and low-frequency measurements, the input resistance plays a dominant role. Higher input impedance reduces the current drawn from the circuit under test, minimizing voltage drop at high-resistance nodes and ensuring accurate measurement of DC parameters like static operating points.

In high-frequency measurements, however, input capacitance becomes the critical limiting factor. This capacitance combines with the signal source impedance to form a low-pass filter, causing signal rise time delays, edge distortion, and even ringing in severe cases. Lower input capacitance yields superior high-frequency response performance.

Probe design often involves trade-offs between input resistance and capacitance. Achieving lower input capacitance typically requires specialized dielectric materials and precision assembly techniques, contributing significantly to the higher cost of high-performance probes. When selecting probes, prioritize models with lower input capacitance based on the frequency components of the signal under test.

Furthermore, proper operating procedures are equally critical. Measures such as performing calibration before use and minimizing ground lead length to reduce loop inductance can effectively suppress the probe's load effect, thereby enhancing measurement authenticity and accuracy.