ADLINK PXI-2208 - Manual (Page 43)

Signal Connections 31
Differential Input Mode
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 3-3 shows the connection of
ground-referenced signal sources under differential input mode.
Figure 3-3: Ground-referenced Source and Differential Input
Ground-referenced Source and Differential Input
Figure 3-4 shows how to connect a floating signal source to the
DAQ-/DAQe-/PXI-2204/2205/2206/2208 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 Instrumentation Amplifier with-
out any resistors. In differential input mode, less noise couples
into the signal connections than in single-ended mode.
Figure 3-4: Floating Source and Differential Input
AIxH
AIxL
x = 0, ..., 31
Ground
Referenced
Signal
Source
To A/D
Converter
AIGND
+
-
Instrumentation
Amplifier
V
cm
Common-
mode noise &
Ground
potential
+
-
Input Multipexer
AIxH
AIxL
x = 0, ..., 31
Ground
Referenced
Signal
Source
To A/D
Converter
AIGND
+
-
Instrumentation
Amplifier
+
-
Input Multipexer