Datasheet
APPLICATION INFORMATION
FULLY DIFFERENTIAL AMPLIFIERS
FULLY DIFFERENTIAL AMPLIFIER
V
IN-
1
2
3
4
8
7
6
5
V
OCM
V
S+
V
OUT+
V
IN+
V
S-
V
OUT-
PD
Applications Section
INPUT COMMON-MODE VOLTAGE RANGE
THS4504
THS4505
www.ti.com
......................................................................................................................................................... SLOS363D – AUGUST 2002 – REVISED MAY 2008
• Additional Reference Material
Differential signaling offers a number of performance
TERMINAL FUNCTIONS
advantages in high-speed analog signal processing
systems, including immunity to external Fully differential amplifiers are typically packaged in
common-mode noise, suppression of even-order eight-pin packages as shown in the diagram. The
nonlinearities, and increased dynamic range. Fully device pins include two inputs (V
IN+
,V
IN –
), two outputs
differential amplifiers not only serve as the primary (V
OUT –
,V
OUT+
), two power supplies (V
S+
, V
S –
), an
means of providing gain to a differential signal chain, output common-mode control pin (V
OCM
), and an
but also provide a monolithic solution for converting optional power-down pin ( PD).
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.
Figure 75. Fully Differential Amplifier Pin Diagram
The THS4504 and THS4505 are intended to be
low-cost alternatives to the THS4500/1/2/3 devices.
A standard configuration for the device is shown in
From a topology standpoint, the THS4504/5 have the
the figure. The functionality of a fully differential
same architecture as the THS4500/1. Specifically, the
amplifier can be imagined as two inverting amplifiers
input common-mode range is designed to include the
that share a common noninverting terminal (though
negative power supply rail.
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
• Fully Differential Amplifier Terminal Functions
(SLOA054 ).
• Input Common-Mode Voltage Range and the
THS4500 Family
• Choosing the Proper Value for the Feedback and
AND THE THS4500 FAMILY
Gain Resistors
The key difference between the THS4500/1 and the
• Application Circuits Using Fully Differential
THS4502/3 is the input common-mode range for the
Amplifiers
four devices. The input common-mode range of the
• Key Design Considerations for Interfacing to an
THS4504/5 is the same as the THS4500/1. The
Analog-to-Digital Converter
THS4502 and THS4503 have an input
• Setting the Output Common-Mode Voltage With
common-mode range that is centered around midrail,
the V
OCM
Input
and the THS4500 and THS4501 have an input
• Saving Power with Power-Down Functionality
common-mode range that is shifted to include the
negative power supply rail. Selection of one or the
• Linearity: Definitions, Terminology, Circuit
other is determined by the nature of the application.
Techniques, and Design Tradeoffs
Specifically, the THS4500 and THS4501 are
• An Abbreviated Analysis of Noise in Fully
designed for use in single-supply applications where
Differential Amplifiers
the input signal is ground-referenced, as depicted in
• Printed-Circuit Board Layout Techniques for
Figure 76 . The THS4502 and THS4503 are designed
Optimal Performance
for use in single-supply or split-supply applications
• Power Dissipation and Thermal Considerations
where the input signal is centered between the
• Power-Supply Decoupling Techniques and
power-supply voltages, as depicted in Figure 77 .
Recommendations
• Evaluation Fixtures, Spice Models, and
Applications Support
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Product Folder Link(s): THS4504 THS4505