User Manual

Measurement Principles
R&S
®
RT-ZS10E/10/20/30
34User Manual 1410.3531.02 ─ 07
0
50
100
150
200
250
300
350
0 100 200 300 400 500 600 700 800 900 1000
Input voltage in mV
Time in ps
Vs
Vin
τ3
V
init
)(
SRFin
RRC

 
RF
S
RF
Sinit
RR
R
VV



where
Figure 4-9: Signal loading caused by the R&S RT ‑ ZS10/20/30 probe at an effective source
impedance 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 (< 100 kHz). A low input resistance can potentially disturb measure-
ments of high-frequency signals as it influences the DC operating point of active
components. This effect is negligible for most applications involving the
R&S RT‑ZS10/20/30 probe due to the high input resistance of the probe (1 MΩ).
4.2.1.2 Input Capacitance
The input capacitance C
in
causes the input impedance to decrease in the
medium-frequency range (100 kHz to 1.0 GHz). Thus, the measurement result
depends on the source impedance of the DUT. The input capacitance affects the
settling time 3τ of the input voltage for fast transients, see Figure 4-9.
Signal Loading of the Input Signal