Datasheet

V
S
Single-Ended
Input
V
S
R
F
R
F
R
G
R
G
THS
4509
Differential
Output
V
OUT+
V
OUT–
+
–
–
+
R
F
V
OUT+
V
OUT–
V
S+
V
IN–
V
S–
R
F
R
G
R
G
V
IN+
THS4509
Differential
Input
Differential
Output
+
–
–
+
÷
÷
ø
ö
ç
ç
è
æ
+
´+
÷
÷
ø
ö
ç
ç
è
æ
+
´=
-+
FG
F
IN
FG
G
OUT
IC
RR
R
V
RR
R
V
V
THS4509
SLOS454H –JANUARY 2005–REVISED NOVEMBER 2009 www.ti.com
APPLICATION INFORMATION
APPLICATIONS
The following circuits show application information for
the THS4509. For simplicity, power-supply
decoupling capacitors are not shown in these
diagrams. Please see the THS4509 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 THS4509 is a fully-differential op amp, and can
be used to amplify differential input signals to
Figure 82. Single-Ended Input to Differential
differential output signals. A basic block diagram of
Output Amplifier
the circuit is shown in Figure 81 (CM input not
shown). The gain of the circuit is set by R
F
divided by
R
G
.
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:
(1)
To determine the V
ICR
of the op amp, the voltage at
Figure 81. Differential Input to Differential Output
the negative input is evaluated at the extremes of
Amplifier
V
OUT+
.
Depending on the source and load, input and output
As the gain of the op amp increases, the input
termination can be accomplished by adding R
IT
and
common-mode voltage becomes closer and closer to
R
O
.
the input common-mode voltage of the source.
Single-Ended Input to Differential Output
Amplifier
The THS4509 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 82 (CM input not shown). The gain of the
circuit is again set by R
F
divided by R
G
.
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