Measurement Principles
R&S
®
RT-ZS60
34
User Manual 1418.7342.02 ─ 04
Figure 4-9: Signal loading caused by the R&S
RT-ZS60 probe at an effective source impe-
dance of 25 Ω
4.2.1.1
Input Resistance
The input resistance R
in
determines the loading of the DUT at DC and low fre-
quencies (<
4
kHz). A low input resistance can potentially disturb measurements
of high-frequency signals as it influences the DC operating point of active compo-
nents. This effect is negligible for most applications involving the R&S
RT-ZS60
probe due to the high input resistance of the probe (1
MΩ).
4.2.1.2
LF Capacitance
The LF capacitance C
LF
causes the input impedance to decrease in the low fre-
quency range (4
kHz to 20
MHz). The LF capacitance affects the settling time of
the loaded input voltage for fast transients, see
Figure 4-9
.
Signal Loading of the Input Signal
