THS4504 Datasheet, PDF (19/45 Pages) National Semiconductor (TI) – WIDEBAND, LOW-DISTORTION, FULLY DIFFERENTIAL AMPLIFIERS

THS4504
THS4505
www.ti.com ......................................................................................................................................................... SLOS363D – AUGUST 2002 – REVISED MAY 2008
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 the flagship 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.
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
Amplifiers
• 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
Techniques, and Design Tradeoffs
• An Abbreviated Analysis of Noise in Fully
Differential Amplifiers
• Printed-Circuit Board Layout Techniques for
Optimal Performance
• Power Dissipation and Thermal Considerations
• Power-Supply Decoupling Techniques and
Recommendations
• Evaluation Fixtures, Spice Models, and
Applications 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-
Figure 75. 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
(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
four devices. The input common-mode range of the
THS4504/5 is the same as the THS4500/1. 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 76. 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 77.
Copyright © 2002–2008, Texas Instruments Incorporated
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Product Folder Link(s): THS4504 THS4505