LOG102 Datasheet, PDF (1/15 Pages) Texas Instruments – LOGARITHMIC AND LOG RATIO AMPLIFIER

LOG102
LOG102
SBOS211A – MARCH 2002
Precision
LOGARITHMIC AND LOG RATIO AMPLIFIER
FEATURES
q EASY-TO-USE COMPLETE LOG RATIO FUNCTION
q OUTPUT AMPLIFIERS FOR SCALING AND
SIGNAL LOSS INDICATION
q HIGH ACCURACY: 0.15% FSO Total Error Over
6 Decades
q WIDE INPUT DYNAMIC RANGE:
6 Decades, 1nA to 1mA
q LOW QUIESCENT CURRENT: 1.25mA
q SO-14 PACKAGE
APPLICATIONS
q ONET, OPTICAL POWER METERS
q LOG, LOG RATIO COMPUTATION:
Communication, Analytical, Medical, Industrial,
Test, General Instrumentation
q PHOTODIODE SIGNAL COMPRESSION AMP
q ANALOG SIGNAL COMPRESSION IN FRONT
OF A/D CONVERTER
q ABSORBANCE MEASUREMENT
q OPTICAL DENSITY MEASUREMENT
V_{LOG OUT} = LOG (I₁/I₂)
V_OUT3 = G • LOG (I₁/I₂), G = 1 +R₂/R₁
I_{1 1}
V+
6
Q₁
Q₂
I₂
14
A₁
DESCRIPTION
The LOG102 is a versatile integrated circuit that computes
the logarithm or log ratio of an input current relative to a
reference current.
The LOG102 is tested over a wide dynamic range of input
signals. In log ratio applications, a signal current can be
generated by a photodiode, and a reference current from a
resistor in series with a precision external voltage reference.
A3 and A4 are identical, uncommitted op amps that can be
used for a variety of functions, such as filtering, offsetting,
adding gain or as a comparator to detect loss of signal.
The output signal at V_{LOG OUT} is trimmed to 1V per decade of
input current. It can be scaled with an output amplifier, either
A3 or A4.
Low dc offset voltage and temperature drift allow accurate
measurement of low-level signals over a wide environmental
temperature range. The LOG102 is specified over the tem-
perature range, 0°C to +70°C, with operation over –40°C to
+85°C.
NOTE: U.S. Patent Pending.
R₁
R₂
C_C
V_{LOG OUT}
5
+IN3
3
–IN3
4
A₃
A₂
7
VOUT3
12
+IN4
A₄
8
VOUT4
A4 can be used
as comparator for
9
10
11
signal loss detect.
GND
V–
–IN4
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Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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.
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Copyright © 2001, Texas Instruments Incorporated