THS4511
www.ti.com
SLOS471–SEPTEMBER 2005
APPLICATION INFORMATION
R
R
F
G
Single-Ended
APPLICATIONS
Input
Differential
5 V
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 differen-
tial operational amplifiers refer to application report
Fully-Differential Amplifiers (SLOA054) .
Output
V
OUT–
+
–
THS4511
R
G
+
–
V
OUT+
Differential Input to Differential Output Amplifier
The THS4511 is a fully differential operational ampli-
fier, 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 RF
divided by RG.
R
F
Figure 44. Single-Ended Input to Differential
Output Amplifier
Input Common-Mode Voltage Range
R
F
The input common-model voltage of a fully differential
operational amplifier is the voltage at the (+) and (–)
input pins of the operational amplifier.
Differential
Differential
5 V
Input
Output
It is important to not violate the input common-mode
voltage range (VICR) of the operational amplifier.
Assuming the operational amplifier is in linear oper-
ation 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.
R
G
V
V
IN+
OUT–
+
–
THS4511
R
G
V
IN–
+
V
OUT+
–
Treating the negative input as a summing node, the
voltage is given by Equation 1:
R
F
æ
ö
æ
ö
R
R
G
F
Figure 43. Differential Input to Differential Ouput
Amplifier
ç
= V
ç
÷
ç
+ V
IN-
ç
÷
V
IC
´
´
OUT+
÷
÷
R
+ R
R
+ R
G
F
G
F
ø
è
ø
è
(1)
To determine the VICR of the operational amplifier, the
voltage at the negative input is evaluated at the
Depending on the source and load, input and output
termination can be accomplished by adding RIT and
RO.
extremes of VOUT+
.
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.
Single-Ended Input to Differential Output
Amplifier
The THS4511 can be used to amplify and convert
single-ended input signals to differential output sig-
nals. 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 RF divided by RG.
16
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