National Instruments PXIe-4467 - Page 15

Figure 8. PXIe-446x Analog Output Block Diagram
1.0 Ω
Output
Configuration
Relay
Output Enable
Relay
Differential
Amplifier
Attenuator
Gain = 0 dB
Gain = –10 dB
Gain = –20 dB
Gain = –30 dB
Low-Pass
Filter
Differential
DAC
5.2 kΩ 5.2 kΩ
50 Ω
1.0 Ω
+AOn
–AOn
Output Configuration Relay
Differential OFF
ONPseudodifferential
BNC Connector Mini-XLR Connector
–AOn
+AOn
–AOn
+AOn
–AOn
1
2
3
+AOn
–AOn
+AOn
Common-
Mode DAC
19.0 Ω
19.0 Ω
280 Ω
280 Ω
40/600 Ω Termination
Selection Relay
The PXIe-446
x output stage is a dierential amplifier. The output stage can be
configured to pseudodierential mode in soware, where the -AO terminal is
internally connected to chassis ground through a 50 Ω resistor. This connection
introduces a gain dierence in the output stage of -22.0 mdB, for which the soware
corrects automatically. Refer to the NI-DAQmx Help for more information about
terminal configuration.
The PXIe-446x output stage can also be configured to pseudodierential mode
by making an external connection between +AOn or -AOn to chassis ground. This
connection introduces a gain change in the output stage of -22.0 mdB, for which the
soware does not correct.
For most applications, configuring the PXIe-446x output stage in dierential mode
will yield the best performance. For improved common-mode noise rejection, it
is highly recommended to make a connection between the chassis ground of the
PXIe-446x and the input device ground. This connection is critical when the input
device is isolated; if this connection is not available, it may be better to configure the
PXIe-446x output stage in pseudodierential mode.
The following figures show the recommended output connections for both
connector types.
© National Instruments
15
PXIe-4466/4467/4468 Getting Started Guide