Common-Mode Rejection - Tektronix P6246 Mode D'emploi

Operating Basics
+ Input
Ground
- - Input
Figure 3: Typical probe input model
As the impedance of the signal source on an input increases, the
more the probe loads the source and reduces the signal amplitude.
The frequency of the signal also affects signal measurement. As the
frequency of the signal increases, the input impedance of the probe
decreases. The lower the impedance of the probe relative to that of
the source, the more the probe loads the circuit under test and
reduces the signal amplitude. For a graph of frequency versus input
impedance, refer to Figure 9 on page 29.

Common-Mode Rejection

The common-mode rejection ratio (CMRR) is the specified ability of
P6246 and P6247 differential probes to reject signals that are
common to both inputs. More precisely, CMRR is the ratio of the
differential gain to the common-mode gain. The higher the ratio, the
greater the ability to reject common-mode signals.
Common mode rejection decreases as the input frequency increases.
Figure 8 on page 28 is a plot of typical CMRR of the probe versus
input frequency. For a more extended discussion of CMRR, see
page 21.
18
1.5 pF
1.5 pF 0.25 pF
100 kΩ
100 kΩ
P6246 & P6247 Instructions