Keysight Technologies N7020A, User Manual

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42 N7020A and N7024A Power Rail Probes User’s Guide
5
Using the Power Rail Probe
To the DC component of a supply voltage, the probe presents a high impedance
and thus low loading (about 50 k
Ω
). To the AC component of the supply voltage,
the probe presents a low 50 Ω impedance. This probe’s low input impedance,
reduces noise on the probe’s output to the oscilloscope thus increasing
measurement range and accuracy.
The following graph shows the probe’s input impedance versus frequency.
Figure 8 Input Impedance Versus Frequency, Z
in
Measured , Z
in
Modeled
(N7020A with N7022A Main Cable)
Minimize Probe Ground Impedance for the Best Signal Fidelity
The N7020A and N7024A probes are single-ended probes that are designed for
measuring small signals riding on large DC voltages. By using the oscilloscope’s
offset knob to offset the DC voltage, you can analyze a power rail using maximum
vertical sensitivity. With no added noise other than a 10% increase to the
oscilloscope channel's noise, due to low attenuation, these probes have very low
input noise. For example, at maximum sensitivity on an S-series oscilloscope, the
input-referred AC
rms
noise is 140 µV
rms
for N7020A.