Datasheet

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DATA CONVERTERS
V
IN
-
+
-
+
DV
DD
V
OCM
AV
SS
AV
DD
A
IN2
A
IN1
3.3 V
V
ref
3.3 V
V
DD
0.1 µF
V
DD
V
IN
-
+
-
+
DV
DD
V
OCM
AV
SS
AV
DD
A
IN2
A
IN1
V
ref
3.3 V
V
DD
0.1 µF
V
CC
R
PU
V
CC
R
PU
R
(g)
R
(g)
V
P
R
f
R
f
V
OUT
V
OUT
R
PU
+
V
P
– V
DD
ǒ
V
IN
– V
P
Ǔ
1
R
(g)
)
ǒ
V
OUT
– V
P
Ǔ
1
R
f
(2)
THS4120
THS4121
SLOS319D – FEBRUARY 2001 – REVISED OCTOBER 2004
APPLICATION INFORMATION (continued)
Data converters are one of the most popular applications for the fully differential amplifiers.
Fully differential amplifiers can operate with a single supply. V
OCM
defaults to the midrail voltage, V
DD
/2. The
differential output may be fed into a data converter. This method eliminates the use of a transformer in the
circuit. If the ADC has a reference voltage output (V
ref
), then it is recommended to connect it directly to the V
OCM
of the amplifier using a bypass capacitor for stability. For proper operation, the input common-mode voltage to
the input terminal of the amplifier should not exceed the common-mode input voltage range.
Figure 19. Differential Amplifier Using a Single Supply
Some single-supply applications may require the input voltage to exceed the common-mode input voltage range.
In such cases, the following circuit configuration is suggested to bring the common-mode input voltage within the
specifications of the amplifier.
Figure 20. Circuit With Improved Common-Mode Input Voltage
The following equation is used to calculate R
PU
:
11
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