LOG112AIDRE4 Datasheet, PDF (1/20 Pages) Texas Instruments – Precision LOGARITHMIC AND LOG RATIO AMPLIFIERS

LOG112
LOG2112
LOG112
LOG2112
SBOS246D – JUNE 2002 – REVISED APRIL 2005
Precision
LOGARITHMIC AND LOG RATIO AMPLIFIERS
FEATURES
DESCRIPTION
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: ±4.5V to ±18V
q PACKAGES: SO-14 (narrow) and SO-16
APPLICATIONS
The LOG112 and LOG2112 are versatile integrated circuits
that compute the logarithm or log ratio of an input current
relative to a reference current. V_LOGOUT of the LOG112 and
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.
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
V_LOGOUT = (0.5V)LOG (I₁/I₂)
V_O3 = K (0.5V)LOG (I₁/I₂), K = 1 + R₂/R₁ ^CC
V+
I₁
Q₁
Q₂
R₁
R₂
V_LOGOUT
+IN3
–IN3
LOG112
I₂
A₁
R_REF
A₂
A₃
V_O3
V_REF
V_REF
GND
V_{REF – GND} V_CM
V–
NOTE: Internal resistors are used to compensate gain change over temperature.
The V_CM pin is internally connected to GND in the LOG2112.
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PRODUCTION DATA information is current as of publication date.
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standard warranty. Production processing does not necessarily include
testing of all parameters.
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