PGA281
SBOS664A –MARCH 2013–REVISED JUNE 2013
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Output Filter
The PGA281 uses a chopper-stabilized architecture for excellent dc stability over temperature and life of
operation. The device also removes 1/f frequency (flicker) noise, and therefore enables both high resolution and
high repeatability for dc measurements. Although the chopper noise components are internally filtered, a minimal
residual amount of high-frequency switching noise appears at the signal outputs. Placing an external, passive,
low-pass filter after the output stage is recommended to remove this switching noise; Figure 42 shows two
examples. This filter can also be used to isolate or decouple the charge switching pulses of an ADC input.
R1
R3
50 W
100 W
VOP
VON
VOP
VON
C1
R2
R4
10 nF
50 W
100 W
C2
10 nF
C3
10 nF
Figure 42. Typical Examples of Recommended Output Filters
Single-Ended Output
The output stage of the PGA281 is designed for highest precision. The fully-differential output avoids grounding
errors and noise, and delivers twice the signal amplitude compared to single-ended signals. However, if desired,
a single-ended output (VOP or VON) can be measured, referred to the voltage at the VOCM pin. The output
stage errors now relate to half the signal amplitude and half the signal gain. Figure 43 shows how the unused
output is unconnected, but not disconnected from error detection. The usable voltage range for the VOCM input
is specified in the Electrical Characteristics and must be observed; that is, the output swing (of both outputs)
should not saturate to the supply. Separate specifications for offset voltage and drift indicate higher offset voltage
at lower gains because some error sources are not cancelled in the output stage connected in single-ended
mode. Note that the gain is one-half of the gain set in reference to the gain table (see Table 1).
15 V
+5 V
In
+
2.5 V
ADC
PGA281
-15 V
Figure 43. Single-Ended Connection Example
18
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