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MATCHING PROBES
Precision measurements start at the probe tip. The probe’s bandwidth must
match that of the oscilloscope (the ‘five times rule’ again), and must not
overload the Device Under Test (DUT).
What you need
 Probes actually become a critical part of the circuit, introducing resistive, capacitive
and inductive loading that alters the measurement. To minimize the effect it’s best to
use probes from the same manufacturer as the scope, forming an integrated solution.
 Loading is critical. Resistive loading of standard passive probes is usually an
acceptable 10 M or better. Capacitive loading of 10, 12 or even 15 picoFarads (pF)
at high frequencies is a real problem though.
 When selecting a mid-range scope choose probes with capacitive loadings of
< 10 pF. The best passive probes offer 1GHz bandwidth with a capacitive load <4 pF.
Probing for answers: Do you plan to measure voltage,
current or both? What frequency is your signal? How
large is the amplitude? Does the DUT have low or high
source impedance? Do you need to measure the signal
differentially? What you want to do determines the probes
you need.
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12 THINGS TO CONSIDER WHEN CHOOSING AN OSCILLOSCOPE
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INTRO