Datasheet

AD8276/AD8277 Data Sheet
Rev. C | Page 16 of 20
APPLICATIONS INFORMATION
CONFIGURATIONS
The AD8276/AD8277 can be configured in several ways (see
Figure 42 to Figure 46). All of these configurations have excellent
gain accuracy and gain drift because they rely on the internal
matched resistors. Note that Figure 43 shows the AD8276/AD8277
as difference amplifiers with a midsupply reference voltage at
the noninverting input. This allows the AD8276/AD8277 to be
used as a level shifter, which is appropriate in single-supply
applications that are referenced to midsupply.
As with the other inputs, the reference must be driven with a
low impedance source to maintain the internal resistor ratio. An
example using the low power, low noise OP1177 as a reference
is shown in Figure 41.
INCORRECT
V
CORRECT
AD8276
OP1177
+
–
V
REF
AD8276
REF
07692-037
Figure 41. Driving the Reference Pin
40kΩ
2
3
5
1
6
40kΩ
40kΩ 40kΩ
–IN
OUT
+IN
V
OUT
= V
IN+
− V
IN−
07692-038
Figure 42. Difference Amplifier, Gain = 1
40kΩ
2
3
5
1
V
REF
= MIDSUPPLY
6
40kΩ
40kΩ 40kΩ
–IN
OUT
+IN
V
OUT
= V
IN+
− V
IN−
07692-039
Figure 43. Difference Amplifier, Gain = 1, Referenced to Midsupply
40kΩ
2
3
5
1
6
40kΩ
40kΩ
40kΩ
IN
OUT
V
OUT
= –V
IN
07692-040
Figure 44. Inverting Amplifier, Gain = −1
40kΩ
5
1
2
3
6
40kΩ
40kΩ 40kΩ
OUT
IN
V
OUT
= V
IN
07692-041
Figure 45. Noninverting Amplifier, Gain = 1
40kΩ
2 5
6
40kΩ
IN
OUT
3
1
40kΩ
40kΩ
V
OUT
= 2V
IN
07692-042
Figure 46. Noninverting Amplifier, Gain = 2
DIFFERENTIAL OUTPUT
Certain systems require a differential signal for better perfor-
mance, such as the inputs to differential analog-to-digital
converters. Figure 47 shows how the AD8276/AD8277 can
be used to convert a single-ended output from an AD8226
instrumentation amplifier into a differential signal. The internal
matched resistors of the AD8276 at the inverting input maximize
gain accuracy while generating a differential signal. The resistors at
the noninverting input can be used as a divider to set and track
the common-mode voltage accurately to midsupply, especially
when running on a single supply or in an environment where
the supply fluctuates. The resistors at the noninverting input
can also be shorted and set to any appropriate bias voltage. Note
that the V
BIAS
= V
CM
node indicated in Figure 47 is internal to
the AD8276 because it is not pinned out.
07692-043
AD8276
AD8226
V
REF
+IN
–IN
R
R
R
R
V
S
–
V
S
+
–OUT
+OUT
V
BIAS
= V
CM
Figure 47. Differential Output With Supply Tracking on Common-Mode
Voltage Reference