Datasheet

V
OCM
+V
S
V
S
R
S
R
g1
R
g2
R
f1
R
f2
+
-
R
T
-
+
Application Circuit for the THS4500 and THS4501,
Featuring Single-Supply Operation With a
Ground-Referenced Input Signal
V
IN-
1
2
3
4
8
7
6
5
V
OCM
V
S+
V
OUT+
V
IN+
V
S-
V
OUT-
PD
Fully Differential Amplifier Pin Diagram
V
OCM
+V
S
V
S
R
S
R
g1
R
g2
R
f1
R
f2
+
-
R
T
-
+
-V
S
Application Circuit for the THS4500 and THS4501,
Featuring Split-Supply Operation With an Input
Signal Referenced at the Midrail
V
OUT)
+
V
IN)
(1–β)–V
IN–
(1–β) ) 2V
OCM
β
2β
V
OUT–
+
–V
IN)
(1–β) ) V
IN–
(1–β) ) 2V
OCM
β
2β
(1)
(2)
THS4502
THS4503
SLOS352E –APRIL 2002–REVISED OCTOBER 2011 www.ti.com
FULLY DIFFERENTIAL AMPLIFIER
TERMINAL FUNCTIONS
Fully differential amplifiers are typically packaged in
eight-pin packages as shown in the diagram. The
device pins include two inputs (V
IN+
,V
IN-
), two outputs
(V
OUT-
,V
OUT+
), two power supplies (V
S+
, V
S-
), an
output common-mode control pin (V
OCM
), and an
optional power-down pin (PD).
Figure 93.
A standard configuration for the device is shown in
the figure. The functionality of a fully differential
amplifier can be imagined as two inverting amplifiers
that share a common noninverting terminal (though
the voltage is not necessarily fixed). For more
information on the basic theory of operation for fully
differential amplifiers, refer to the Texas Instruments
application note titled Fully Differential Amplifiers,
literature number SLOA054.
INPUT COMMON-MODE VOLTAGE RANGE
Figure 94.
AND THE THS4500 FAMILY
The key difference between the THS4500/1 and the
Equations 1-5 allow for calculation of the required
THS4502/3 is the input common-mode range for the
input common-mode range for a given set of input
two devices. The THS4502 and THS4503 have an
conditions.
input common-mode range that is centered around
The equations allow calculation of the input common-
midrail, and the THS4500 and THS4501 have an
mode range requirements given information about the
input common-mode range that is shifted to include
input signal, the output voltage swing, the gain, and
the negative power supply rail. Selection of one or the
the output common-mode voltage. Calculating the
other is determined by the nature of the application.
maximum and minimum voltage required for V
N
and
Specifically, the THS4500 and THS4501 are
V
P
(the amplifier's input nodes) determines whether
designed for use in single-supply applications where
or not the input common-mode range is violated or
the input signal is ground-referenced, as depicted in
not. Four equations are required. Two calculate the
Figure 93. The THS4502 and THS4503 are designed
output voltages and two calculate the node voltages
for use in single-supply or split-supply applications
at V
N
and V
P
(note that only one of these needs
where the input signal is centered between the power
calculation, as the amplifier forces a virtual short
supply voltages, as depicted in Figure 94.
between the two nodes).
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