15.2.4
Passive, differential matched isolated voltage probes
Passive, differential matched isolated voltage probes are used in series with
differential amplifiers and divide a differential input signal by a specific factor.
10 x Udiff
Udiff
(+)
(-)
(-)
Passive probe
GND
Differential amplifier
9M
9M
900K
900K
10
0K
10
0K
(+)
(+)
(-)
Figure 15.10:
Typical example of a passive differential voltage probe
Passive, differential matched isolated voltage probes are – in theory – simply
a pair of “normal” voltage probes.
They add passive in
-
line resistors in series with both the positive and the
negative inputs of a differential amplifier. Together with the input resistor of the
amplifier, they form a voltage divider on each input side so that the voltage in
series with the amplifier itself is divided. As there is also a capacitive component
in this divider, the input capacitance of the amplifier and the so
-
called
“compensation range” of the probe need to match.
As two of these probes are used, one with each input terminal, the probes
themselves need to “match” as closely as possible. Otherwise, the two input
terminals are divided differently. Therefore, the probes are typically
manufactured (and sold) in pairs and called “matched”. By selecting higher
resistance probes, the divider ratio increases so that large input ranges are
possible. Passive, differential matched isolated voltage probes typically
decrease the overall accuracy and the CMRR of the system.
GEN3t
394
I3995-3.1 en HBM: public