Measurement Principles
R&S
®
RT-ZPR20
R&S
®
RT-ZPR40
24
User Manual 1800.5035.02 ─ 03
5
Measurement Principles
The R&S
RT-ZPR20/40 power-rail probe provides an electrical connection
between the DUT and the oscilloscope. The probe transfers the voltage of the
electrical signal tapped off the DUT to the oscilloscope, where it is displayed
graphically.
Although a probe has a wide variety of specifications, these specifications can be
grouped into two classes of basic requirements:
●
High signal integrity of the transferred signal: With an ideal probe, the output
signal that is transferred to the base unit would be identical to the input signal
between the probe tips. Furthermore, signal integrity would be extremely high.
Every real probe, however, transfers the input signal in altered form. A good
probe causes only minimum alterations. How the probe can fulfill this require-
ment is mainly determined by its bandwidth.
●
Low loading of the input signal: Every probe is a load for the signal to be mea-
sured. This means that the signal to be measured changes as soon as the
probe is connected. A good probe should cause only a minimum change to
the signal, so that the function of the DUT is not adversely affected. How well
the probe can fulfill this requirement is mainly determined by its input impe-
dance.
The parameters of a probe are usually specified for a minimized connection
between the probe and the DUT. With longer connections, the connection induc-
tance has a significant effect on the measurement. The high-frequency behavior
of the power rail probe is typically characterized with 0 Ω source impedance.
shows the R&S
RT-ZPR20/40 power-rail probe that is connected to the
DUT.
Figure 5-1: Equivalent circuit model of the R&S
RT-ZPR20/40 probe
