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®
R&S
RT-ZD40
5.1.3
CMRR
The CMRR is very good for low-frequency signals, but it continuously decreases
for higher frequencies. Therefore, the CMRR is usually specified as a function of
frequency.
The
figure 5-5
shows a typical CMRR for an R&S RT-ZD40 differential probe with
a very symmetrical connection to the DUT. An asymmetrical connection to the
test point can decrease the CMRR. To achieve the best possible CMRR, the con-
nection to the DUT should always be as symmetrical as possible.
Fig. 5-5: Typical CMRR of the R&S RT-ZD40 probe as a function of frequency
5.2
Signal Loading of the Input Signal
The previous section explained the transfer function and step response of the
probe. This section describes how the probe influences the input signal. The input
signal loading caused by the probe is determined by its input impedance. In gen-
eral, the probe causes only low signal loading because its input impedance is
usually much greater than the source impedance of the test circuit.
User Manual 1410.5363.02 ─ 03
Measurement Principles
Signal Loading of the Input Signal
39
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