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4-11
Connecting an Analog Input Signal to a Differential Input
For differential input configurations, you must provide a bias current
return path. If at least one channel is unused or configured for
single-ended input, use the negative side of that channel as the low-level
analog common; otherwise, use the digital common.
Figure 4-10 illustrates how to connect an analog input signal to
differential analog input channel 0 on a DAS-8PGA board for output
resistances both less than and greater than 100
Ω
. Since analog input
channel 7 is not used, the bias current return path is connected to the
negative side of channel 7.
Figure 4-10. Differential Input
Note:
For output resistances greater than 100
Ω,
it is recommended that
the sum of the resistors used be at least 5,000 times greater than the
source output resistor.
+
−
Voltage
Source
+
−
Pin 37
Chan 0(+)
Pin 19
Chan 0(
−
)
DAS-8/PGA Board
Pin 12
Chan 7(
−
)
+
−
Voltage
Source
+
−
Pin 37
Chan 0(+)
Pin 19
Chan 0(
−
)
DAS-8/PGA Board
Pin 12
Chan 7(
−
)
R
OUT
> 100
Ω
250 k
Ω
250 k
Ω
R
OUT
< 100
Ω
250 k
Ω
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