THS4500 Datasheet, PDF (21/37 Pages) Texas Instruments – WIDEBAND, LOW DISTORTION FULLY DIFFERENTIAL AMPLIFIERS

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THS4500
THS4501
SLOS350D − APRIL 2002 − REVISED JANUARY 2004
APPLICATION INFORMATION
FULLY DIFFERENTIAL AMPLIFIERS
Differential signaling offers a number of performance
advantages in high-speed analog signal processing
systems, including immunity to external common-mode
noise, suppression of even-order nonlinearities, and
increased dynamic range. Fully differential amplifiers not
only serve as the primary means of providing gain to a
differential signal chain, but also provide a monolithic
solution for converting single-ended signals into
differential signals for easier, higher performance
processing. The THS4500 family of amplifiers contains
products in Texas Instruments’ expanding line of
high-performance fully differential amplifiers. Information
on fully differential amplifier fundamentals, as well as
implementation specific information, is presented in the
applications section of this data sheet to provide a better
understanding of the operation of the THS4500 family of
devices, and to simplify the design process for designs
using these amplifiers.
Applications Section
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.
D Fully Differential Amplifier Terminal Functions
D Input Common-Mode Voltage Range and the
THS4500 Family
D Choosing the Proper Value for the Feedback and
Gain Resistors
D Application Circuits Using Fully Differential
Amplifiers
D Key Design Considerations for Interfacing to an
Analog-to-Digital Converter
D Setting the Output Common-Mode Voltage With the
V_OCM Input
D Saving Power with Power-Down Functionality
D Linearity: Definitions, Terminology, Circuit
Techniques, and Design Tradeoffs
D An Abbreviated Analysis of Noise in Fully
Differential Amplifiers
D Printed-Circuit Board Layout Techniques for Optimal
Performance
D Power Dissipation and Thermal Considerations
D Power Supply Decoupling Techniques and
Recommendations
D Evaluation Fixtures, Spice Models, and Applications
Support
D Additional Reference Material
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 97. 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 98.
RS
Rg1
Rf1
VS
RT
+VS
+−
VOCM
−+
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−,
Rg2
Rf2
Application Circuit for the THS4500 and THS4501,
Featuring Single-Supply Operation With a
Ground-Referenced Input Signal
Figure 97
21