THS4513_14 Datasheet, PDF (25/42 Pages) Texas Instruments – WIDEBAND, LOW-NOISE, LOW-DISTORTION FULLY-DIFFERENTIAL AMPLIFIER

THS4513
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SLOS472E – AUGUST 2005 – REVISED JANUARY 2013
APPLICATION INFORMATION
APPLICATIONS
The following circuits show application information for
the THS4513. For simplicity, power-supply
decoupling capacitors are not shown in these
diagrams. Please see the THS4513 EVM section for
recommendations. For more detail on the use and
operation of fully-differential op amps refer to the
application report, Fully-Differential Amplifiers
(SLOA054).
Differential Input to Differential Output Amplifier
The THS4513 is a fully-differential op amp, and can
be used to amplify differential input signals to
differential output signals. A basic block diagram of
the circuit is shown in Figure 76 (CM input not
shown). The gain of the circuit is set by R_F divided by
R_G.
Differential
Input
R_F
V_S+
Differential
Output
Amplifier
The THS4513 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 77 (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_F
V_S
Differential
Output
+–
V_OUT–
R_G
THS 4513
–+
V_OUT+
V_S
R_F
Figure 77. Single-Ended Input to Differential
Output Amplifier
R_G
V_IN+
R_G
V_IN–
+–
THS4513
–+
V_OUT–
V_OUT+
V_S–
R_F
Figure 76. 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
Input Common-Mode Voltage Range
The input common-model voltage of a fully differential
op amp is the voltage at the '+' and '–' input pins of
the op amp.
It is important to not violate the input common-mode
voltage range (V_ICR) of the op amp. Assuming the op
amp 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 will determine the input
common-mode voltage of the op amp.
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 op amp, the voltage at
the negative input is evaluated at the extremes of
V_OUT+.
As the gain of the op amp increases, the input
common-mode voltage becomes closer and closer to
the input common-mode voltage of the source.
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