ADLINK cPCI-9116 - Manual (Page 27)

Signal Connections
• 17
Differential input mode
The differential input mode provides two inputs that respond to signal voltage
differences between them. If the signal source is ground- referenced, the
differential mode can be used for common-mode noise rejection. Figure 5
shows the connection of ground-referenced signal sources under differential
input mode.
AIxH
AIxL
x = 0, ..., 31
Ground
Referenced
Signal
Source
To A/D
Converter
AGND
+
-
Instrumentation
Amplifier
V
cm
Common-
mode noise &
Ground
potential
+
-
Input Multipexer
Figure 5: Ground-referenced source and differential input
Fig 6 shows how to connect a floating signal source to the 9116 card in
differential input mode. For floating signal sources, a resistor is required on
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, simply connect the negative side of the signal to AGND as well
as the negative input of the Instrumentation Amplifier, without any resistors. In
differential input mode, less noise is coupled into the signal connections than in
single-ended mode.
AIxH
AIxL
x = 0, ..., 31
Ground
Referenced
Signal
Source
To A/D
Converter
AGND
+
-
Instrumentation
Amplifier
+
-
Input Multipexer
Figure 6: Floating source and differential input