Owner's manual

Signal Connections 21
3.2.2 Input Connect Configurations - Differential Input
Mode
Figure 3-1: Ground-referenced Source and Differential Input
The differential input mode provides two inputs that respond to
signal voltage difference between them. If the signal source is
ground-referenced, the differential mode can be used for the com-
mon-mode noise rejection. Figure 3-1 shows the connection of
ground-referenced signal sources under differential input mode.
Figure 3-2 shows how to connect a floating signal source to the
PXI-2020/2022 card in differential input mode. For floating signal
sources, you need to add a resistor at each channel to provide a
bias return path. The resistor value should be about 100 times the
equivalent source impedance. If the source impedance is less
than 100ohms, you can simply connect the negative side of the
signal to AIGND as well as the negative input of the Instru-menta-
tion Amplifier without any resistors. In differential input mode, less
noise couples into the signal connections than in single-ended
mode.
A
Ix
H
A
IxL
x
= 0, ..., 31
G
round
Referenced
S
ignal
S
ource
To A/D
Converter
A
IGND
+
-
Instrumentation
A
mplifier
V
cm
Common-
mode noise &
Ground
potential
+
-
Input Multiplexer