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 (VIN+,VIN–), two outputs

differential amplifiers not only serve as the primary

(VOUT–,VOUT+), two power supplies (VS+, VS–), an

means of providing gain to a differential signal chain,

output common-mode control pin (VOCM), 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 VOCM 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

Copyright © 2002–2008, Texas Instruments Incorporated

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