THS4140 Datasheet, PDF (12/33 Pages) Texas Instruments – HIGH SPEED FULLY DIFFERENTIAL I/O AMPLIFIERS

THS4140
THS4141
SLOS320F – MAY 2000 – REVISED JANUARY 2006
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APPLICATION INFORMATION (continued)
DATA CONVERTERS
Data converters are one of the most popular applications for the fully differential amplifiers. Figure 22 shows a
typical configuration of a fully differential amplifier attached to a differential ADC.
0.1 µF
V_CC
5V
V_IN
+-
V_OCM
-+
-5 V
V_CC-
V_DD
AV_DD DV_DD
A_IN1
A_{IN2 AVSS}
V_ref
Figure 22. Fully Differential Amplifier Attached to a Differential ADC
Fully differential amplifiers can operate with a single supply. V_OCM defaults to the midrail voltage, V_CC/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.
0.1 µF
V_CC
5V
V_IN
+-
V_OCM
-+
V_DD
AV_DD DV_DD
A_IN1
A_{IN2 AVSS}
V_ref
Figure 23. Fully 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.
0.1 µF
V_CC
R_f V_CC
R_PU
R_g
5V
V_IN
+
V_{P VOCM}
-
R_g
R_PU
V_CC
-+
R_f
V_DD
V_OUT
AV_DD
A_IN
DV_DD
V_OUT ^{AIN AVSS}
V_ref
Figure 24. Circuit With Improved Common-Mode Input Voltage
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