Measurement Principles
R&S
®
RT-ZZ80
22
User Manual 1409.7689.02 ─ 02
2V
S
50 Ω
50 Ω
Circuit ground
Probe ground
R
in
500 Ω
C
in
0.3 pF
DUT
L
con
V
in
R
S
R
L
Fig. 4-1: Equivalent circuit model of the R&S
RT-ZZ80 probe
Table 4-1: Designations
Abbreviation
Description
V
S
Voltage at the test point without probe connected
V
in
Voltage at the test point with probe connected,
corresponds to the input voltage of the probe
R
S
Source resistance of the DUT
R
L
Load resistance of the DUT
R
in
Input resistance of the probe
C
in
Input capacitance of the probe
L
con
Connection inductance,
depends on the type of connection
In a 50 Ω system, the output resistance of the source, the load resistance of the
DUT and the characteristic impedance of all lines equal exactly 50 Ω. However,
the behavior of the probe in the circuit is determined by the effective source impe-
dance which is the impedance present in the DUT between the probe tip and
ground.
Effective source impedance:
25
||
L
S
S
R
R
R
