LOG112

LOG2112

SBOS246C – JUNE 2002 – REVISED APRIL 2003

www.ti.com

DESCRIPTION

The LOG112 and LOG2112 are versatile integrated circuits

that compute the logarithm or log ratio of an input current

LOG2112 are trimmed to 0.5V per decade of input current,

ensuring high precision over a wide dynamic range of input

signals.

The LOG112 and LOG2112 features a 2.5V voltage refer-

ence that may be used to generate a precision current

reference using an external resistor.

Low DC offset voltage and temperature drift allow accurate

measurement of low-level signals over the specified tem-

perature range of –5

°C to +75°C.

FEATURES

q EASY-TO-USE COMPLETE FUNCTION

q OUTPUT SCALING AMPLIFIER

q ON-CHIP 2.5V VOLTAGE REFERENCE

q HIGH ACCURACY: 0.2% FSO Over 5 Decades

q WIDE INPUT DYNAMIC RANGE:

7.5 Decades, 100pA to 3.5mA

q LOW QUIESCENT CURRENT: 1.75mA

q WIDE SUPPLY RANGE:

q PACKAGES: SO-14 (narrow) and SO-16

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

Copyright © 2002-2003, Texas Instruments Incorporated

Precision

LOGARITHMIC AND LOG RATIO AMPLIFIERS

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

APPLICATIONS

q LOG, LOG RATIO:

Communication, Analytical, Medical, Industrial,

Test, General Instrumentation

q PHOTODIODE SIGNAL COMPRESSION AMP

q ANALOG SIGNAL COMPRESSION IN FRONT

OF ANALOG-TO-DIGITAL (A/D) CONVERTER

q ABSORBANCE MEASUREMENT

q OPTICAL DENSITY MEASUREMENT

LOG1

12

LOG2

112

A

2

A

1

Q

1

Q

2

C

C

I

1

V

REF – GND

NOTE: Internal resistors are used to compensate gain change over temperature.

The V

V

O3

V+

GND

LOG112

V

V

A

3

R

2

R

1

V

REF

R

REF

+IN3

V

LOGOUT

–IN3

V–

V

CM

I

2

V

REF