Passive Differential Voltage Probes - HBM Genesis GEN5i User Manual

GEN5i
D.2.4

Passive differential voltage probes

Passive differential voltage probes are used in front of differential amplifiers and
divide down a differential input signal by a specific factor.
Figure D.11: Typical example of a passive differential voltage probe
Passive differential voltage probes are – in theory – just a pair of "normal"
voltage probes.
They add passive in-line resistors in front of both the positive as well as 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
front of the amplifier itself gets divided down. 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 itself
needs to "match" as closely as possible, as otherwise the two input terminals
are divided down differently.
Therefore the probes are typically manufactured (and sold) in pairs and called
"matched".
By selecting higher resistance probes the divider ratio gets bigger, so that pretty
large input ranges are possible.
Passive differential voltage probes typically decrease the overall accuracy and
the CMRR of the system.
520 I2679-4.0 en