THS4511_14 Datasheet, PDF (19/36 Pages) Texas Instruments – WIDEBAND, LOW-NOISE, LOW-DISTORTION FULLY-DIFFERENTIAL AMPLIFIER

THS4511
www.ti.com
SLOS471E – SEPTEMBER 2005 – REVISED NOVEMBER 2009
APPLICATION INFORMATION
APPLICATIONS
The following circuits show application information for
the THS4511. For simplicity, power-supply
decoupling capacitors are not shown in these
diagrams. For more detail on the use and operation
of fully-differential operational amplifiers refer to
application report Fully-Differential Amplifiers
(SLOA054).
Differential Input to Differential Output Amplifier
The THS4511 is a fully-differential operational
amplifier, and can be used to amplify differential input
signals to differential output signals. A basic block
diagram of the circuit is shown in Figure 43 (CM input
not shown). The gain of the circuit is set by R_F
divided by R_G.
Differential
Input
R_F
5V
Differential
Output
R_G
V_IN+
R_G
V_IN–
+–
THS4511
–+
V_OUT–
V_OUT+
R_F
Figure 43. Differential Input to Differential Output
Amplifier
Depending on the source and load, input and output
termination can be accomplished by adding R_IT and
R_O.
Single-Ended Input to Differential Output
Amplifier
The THS4511 can be used to amplify and convert
single-ended input signals to differential output
signals. A basic block diagram of the circuit is shown
in Figure 44 (CM input not shown). The gain of the
circuit is again set by R_F divided by R_G.
Single-Ended
R_G
Input
R_G
R_F
5V
+–
THS4511
–+
Differential
Output
V_OUT–
V_OUT+
R_F
Figure 44. Single-Ended Input to Differential
Output Amplifier
Input Common-Mode Voltage Range
The input common-model voltage of a fully-differential
operational amplifier is the voltage at the (+) and (–)
input pins of the operational amplifier.
It is important to not violate the input common-mode
voltage range (V_ICR) of the operational amplifier.
Assuming the operational amplifier is in linear
operation the voltage across the input pins is only a
few millivolts at most. So finding the voltage at one
input pin determines the input common-mode voltage
of the operational amplifier.
Treating the negative input as a summing node, the
voltage is given by Equation 1:
V_IC
=
ççèæ ^VOUT+
´
R_G
R_G + R_F
÷÷øö
+
ççèæ ^VIN-
´
R_F
R_G + R_F
÷÷øö
(1)
To determine the V_ICR of the operational amplifier, the
voltage at the negative input is evaluated at the
extremes of V_OUT+.
As the gain of the operational amplifier increases, the
input common-mode voltage becomes closer and
closer to the input common-mode voltage of the
source.
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