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Chapter 2 Configuration and Installation
©
National Instruments Corporation 2-29 AT-MIO-16X User Manual
Common-Mode Signal Rejection Considerations
Figures 2-7 and 2-8, located earlier in this chapter, show connections
for signal sources that are already referenced to some ground point with
respect to the AT-MIO-16X. In these cases, the PGIA can reject any
voltage caused by ground potential differences between the signal
source and the AT-MIO-16X. In addition, with differential input
connections, the PGIA can reject common-mode noise pickup in the
leads connecting the signal sources to the AT-MIO-16X.
The common-mode input range of the AT-MIO-16X PGIA is defined as
the magnitude of the greatest common-mode signal that can be rejected.
The PGIA can reject common-mode signals as long as V+
in
and V–
in
are both in the range ±11 V. Thus, the common-mode range for the
AT-MIO-16X depends on the size of the differential input signal
(V
diff
= V+
in
– V–
in
). The exact formula for the allowed common-mode
input range is as follows:
V
cm-max
= ±(11 V – V
diff
/2)
With a differential voltage of 10 V, the maximum possible
common-mode voltage is ±6 V. The common-mode voltage is measure
with respect to the AT-MIO-16X ground and can be calculated by the
following formula:
where V+
in
is the signal at the positive (+) input of the PGIA and –
in
is
the signal at the negative (–) input of the PGIA. Both V+
in
and V–
in
are
measured with respect to AI GND.
Analog Output Signal Connections
DAC0 OUT is the voltage output signal for analog output Channel 0.
DAC1 OUT is the voltage output signal for analog output Channel 1.
EXTREF is the external reference input for both analog output
channels. Each analog output channel must be configured individually
for external reference selection in order for the signal applied at the
external reference input to be used by that channel. Analog output
configuration instructions are in the Analog Output Configuration
section earlier in this chapter.
V
cm actual–
V+
in
V–
in
+
()
2
-----------------------------------=