Measurement Principles
R&S
®
RT-ZZ80
30
User Manual 1409.7689.02 ─ 02
4.2.2.1
Input Resistance R
in
The input resistance determines the loading of the DUT at DC and frequencies up
to 1
GHz. In this area, the input impedance is near-constant. For DC signals, the
input resistance is 500
Ω
.
4.2.2.2
Input Capacitance C
in
and Minimum Input Impedance |Z
min
|
The input capacitance C
in
causes the input impedance to decrease for high fre-
quencies above 1
GHz. C
in
is very low - typically under 300
fF. This low input
capacitance minimizes the load of high-frequency signals.
The minimum input impedance |Z
min
| mainly depends on the the connection
inductance and the connection type. An overview is given in
4.3
Attenuation Dependence on Source Impedance
The previous sections made clear that probes exert a load on the signal to be
measured and change its characteristic. The signal at the test point where the
probe makes contact (V
in
) is therefore different from the signal that was present
before the probe was connected (V
S
).
In contrast to most other probes, the load of the R&S
RT-ZZ80 is not negligible
for DC and low-frequency signals. Therefore, the attenuation of the probe
depends on the impedance of the signal source. The
ded and loaded input voltages as well as the output voltage of the probe in an
50
Ω
environment.
For the R&S
RT-ZZ80, the output signal is a good representation of the loaded
input signal. The loaded input signal differs from the unloaded signal mainly by a
lower voltage swing, while the shapes of both signals are almost identical.
Attenuation Dependence on Source Impedance
