THS4505 Datasheet, PDF (20/38 Pages) Texas Instruments – WIDEBAND, LOW-DISTORTION, FULLY DIFFERENTIAL AMPLIFIERS

THS4504
THS4505
SLOS363C – AUGUST 2002 – REVISED MARCH 2004
www.ti.com
APPLICATION INFORMATION
FULLY DIFFERENTIAL AMPLIFIERS
Differential signaling offers a number of performance
advantages in high-speed analog signal processing
systems, including immunity to external com-
mon-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 the flagship products in
Texas Instruments' expanding line of
high-performance fully differential amplifiers. Infor-
mation on fully differential amplifier fundamentals, as
well as implementation-specific information, is pres-
ented 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.
The THS4504 and THS4505 are intended to be
low-cost alternatives to the THS4500/1/2/3 devices.
From a topology standpoint, the THS4504/5 have the
same architecture as the THS4500/1. Specifically, the
input common-mode range is designed to include the
negative power supply rail.
Applications Section
• Fully Differential Amplifier Terminal Functions
• Input Common-Mode Voltage Range and the
THS4500 Family
• Choosing the Proper Value for the Feedback and
Gain Resistors
• Application Circuits Using Fully Differential Ampli-
fiers
• Key Design Considerations for Interfacing to an
Analog-to-Digital Converter
• Setting the Output Common-Mode Voltage With
the V_OCM Input
• Saving Power with Power-Down Functionality
• Linearity: Definitions, Terminology, Circuit Tech-
niques, and Design Tradeoffs
• An Abbreviated Analysis of Noise in Fully Differ-
ential Amplifiers
• Printed-Circuit Board Layout Techniques for Opti-
mal Performance
• Power Dissipation and Thermal Considerations
• Power Supply Decoupling Techniques and Rec-
ommendations
• Evaluation Fixtures, Spice Models, and Appli-
cations Support
• Additional Reference Material
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 infor-
mation on the basic theory of operation for fully
differential amplifiers, refer to the Texas Instruments
application note titled Fully Differential Ampli-
fiers(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 input common-mode range of the
THS4504/5 is the same as the THS4500/1. The
THS4502 and THS4503 have an input com-
mon-mode range that is centered around midrail, and
the THS4500 and THS4501 have an input com-
mon-mode range that is shifted to include the nega-
tive power supply rail. Selection of one or the other is
determined by the nature of the application. Specifi-
cally, the THS4500 and THS4501 are designed for
use in single-supply applications where the input
signal is ground-referenced, as depicted in Figure 75.
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 76.
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