THS4502 Datasheet, PDF (22/49 Pages) Texas Instruments – WIDEBAND, LOW-DISTORTION FULLY DIFFERENTIAL AMPLIFIERS

THS4502
THS4503
SLOS352E – APRIL 2002 – REVISED OCTOBER 2011
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).
V_IN- 1
V_{OCM 2}
V_{S+ 3}
V_OUT+ 4
8 V_IN+
7 PD
6 V_S-
5 V_OUT-
Fully Differential Amplifier Pin Diagram
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
AND THE THS4500 FAMILY
The key difference between the THS4500/1 and the
THS4502/3 is the input common-mode range for the
two devices. The THS4502 and THS4503 have an
input common-mode range that is centered around
midrail, and the THS4500 and THS4501 have an
input common-mode range that is shifted to include
the negative power supply rail. Selection of one or the
other is determined by the nature of the application.
Specifically, the THS4500 and THS4501 are
designed for use in single-supply applications where
the input signal is ground-referenced, as depicted in
Figure 93. The THS4502 and THS4503 are designed
for use in single-supply or split-supply applications
where the input signal is centered between the power
supply voltages, as depicted in Figure 94.
www.ti.com
R_S
R_g1
R_f1
V_S
R_T
+V_S
+-
V_OCM
-+
R_g2
R_f2
Application Circuit for the THS4500 and THS4501,
Featuring Single-Supply Operation With a
Ground-Referenced Input Signal
Figure 93.
R_S
R_g1
R_f1
V_S
R_T
+V_S
+-
V_OCM
-+
-V_S
R_g2
R_f2
Application Circuit for the THS4500 and THS4501,
Featuring Split-Supply Operation With an Input
Signal Referenced at the Midrail
Figure 94.
Equations 1-5 allow for calculation of the required
input common-mode range for a given set of input
conditions.
The equations allow calculation of the input common-
mode range requirements given information about the
input signal, the output voltage swing, the gain, and
the output common-mode voltage. Calculating the
maximum and minimum voltage required for V_N and
V_P (the amplifier's input nodes) determines whether
or not the input common-mode range is violated or
not. Four equations are required. Two calculate the
output voltages and two calculate the node voltages
at V_N and V_P (note that only one of these needs
calculation, as the amplifier forces a virtual short
between the two nodes).
V _OUT)
+
V_IN)(1–β)–V_IN–(1–β) ) 2V_OCMβ
2β
(1)
V _OUT–
+
–V_IN)(1–β) ) V_IN–(1–β) ) 2V_OCMβ
2β
(2)
22
Submit Documentation Feedback
Copyright © 2002–2011, Texas Instruments Incorporated
Product Folder Link(s): THS4502 THS4503