Datasheet

ADAS3022 Data Sheet
Rev. B | Page 26 of 40
Fully Differential, Antiphase Signals with a
Nonzero Common Mode
For a pair of 5.12 V p-p differential antiphase signals with a
nonzero common mode (dc common-mode voltage of 7 V in
this example), the maximum differential voltage across the
inputs is 5.12 V (dc common-mode voltage is rejected), and
the PGIA gain configuration should be set to 010.
ADAS3022
INx
+
INx+
0V
5.12V p-p
5.12V p-p
INx–
INx–
V
CM
= 7V
V
CM
10516-010
Figure 57. Differential, Antiphase Inputs with a Nonzero Common Mode
Differential, Nonantiphase Signals with a
Zero Common Mode
For a pair of 10.24 V p-p differential nonantiphase signals with
a zero common mode, the maximum differential voltage across
the inputs is 10.24 V, and the PGIA gain configuration should
be set to 001.
ADAS3022
INx+
+5.12V
10.24V p-p
0V
INx–
–5.12V
10.24V p-p
10516-011
INx
+
INx–
Figure 58. Differential, Nonantiphase Inputs with a Zero Common Mode
Single-Ended Signals with a Nonzero DC Offset
(Asymmetrical)
When a 12 V p-p signal with a 6 V dc level-shift is connected to
one input (INx+) and the dc ground sense of the signal is
connected to INx− or COM, the PGIA gain configuration is set
to 000 for the ±24.576 V range because the maximum differential
voltage across the inputs is 12 V p-p and only half the codes
available for the transfer function are used.
ADAS3022
INx+
INx+
+12V
12V p-p
0V
V
OFF
V
OFF
INx–
INx–
10516-012
Figure 59. Typical Single-Ended Unipolar Input—Uses Only Half the Codes
Single-Ended Signals with a 0 V DC Offset (Symmetrical)
Compared with the example in the Single-Ended Signals with a
Nonzero DC Offset (Asymmetrical) section, a better solution
for single-ended signals, if possible, is to remove as much dc
offset as possible between INx+ and INx− to produce a bipolar
input voltage that is symmetric around the ground sense. In this
example, the differential voltage across the inputs is never greater
than ±0.64 V, and the PGIA gain configuration is set to 101 for
the 1.28 V p-p range. This scenario uses all of the codes
available for the transfer function, making full use of the
allowable differential input range.
ADAS3022
INx
+
INx+
+0.64V
1.28V p-p
–0.64V
INx–
INx–
10516-013
Figure 60. Better Single-Ended Configuration—Uses All Codes
Notice that the voltages in this example are not integer values
due to the 4.096 V reference and the PGIA scaling ratios.
Multiplexer
The ADAS3022 uses a high voltage, high performance, low
charge injection multiplexer and a total of nine inputs (IN[7:0]
and COM). Using the INx and COM bits of the configuration
register, the ADAS3022 is configurable for differential inputs
between any of the eight input channels (IN[7:0]) and COM or
for up to four input pairs. Figure 61 shows various methods for
configuring the analog inputs for the type of channel (single or
paired). Refer to the Configuration Register section for more
information.
The analog inputs can be configured as follows:
 Figure 61A: IN[7:0] referenced to a system ground.
 Figure 61B: IN[7:0] with a common reference point.
 Figure 61C: IN[7:0] differential pairs. For pairs, COM = 0.
The positive channel is configured with INx. If INx is even,
then IN0, IN2, IN4, and IN6 are used. If INx is odd, then
IN1, IN3, IN5, and IN7 are used, as indicated by the channels
with parentheses in Figure 61C. For example, for the IN0/IN1
pair with the positive channel on IN0, INx = 000
2
. For the
IN4/IN5 pair with the positive channel on IN5, INx = 101
2
.
Note that when the channel sequencer is used, as detailed in
the Channel Sequencer Details section, the positive channels
are always IN0, IN2, IN4, and IN6.
 Figure 61D: inputs configured in a combination of any of
the preceding configurations (showing that the ADAS3022
can be configured dynamically).