Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsLinear ICsLinear IC - Op-amp Log ratio amplifier SOIC 8

FEATURES

●

EASY-TO-USE COMPLETE CORE FUNCTION

● HIGH ACCURACY: 0.01% FSO Over 5 Decades

● WIDE INPUT DYNAMIC RANGE:

7.5 Decades, 100pA to 3.5mA

● LOW QUIESCENT CURRENT: 1mA

● WIDE SUPPLY RANGE: ±4.5V to ±18V

Precision

LOGARITHMIC AND LOG RATIO AMPLIFIER

DESCRIPTION

The LOG101

is a versatile integrated circuit that computes

the logarithm or log ratio of an input current relative to a

reference current.

The LOG101 is tested over a wide dynamic range of input

signals. In log ratio applications, a signal current can come

from a photodiode, and a reference current from a resistor in

series with a precision external reference.

The output signal at V

OUT

is trimmed to 1V per decade of input

current allowing seven decades of input current dynamic

range.

Low DC offset voltage and temperature drift allow accurate

measurement of low-level signals over a wide environmental

temperature range. The LOG101 is specified over the tem-

perature range –5°C to +75°C, with operation over

–40°C to +85°C.

APPLICATIONS

● LOG, LOG RATIO COMPUTATION:

Communication, Analytical, Medical, Industrial,

Test, and General Instrumentation

● PHOTODIODE SIGNAL COMPRESSION AMPS

● ANALOG SIGNAL COMPRESSION IN FRONT

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

LOG101

www.ti.com

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.

SBOS242B – MAY 2002 – REVISED JUNE 2004

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.

Note: Protected under US Patent #6,667,650; other patents pending.

V–

OUT

V+

GND

LOG101

OUT

= (1V) • LOG (I

)

All trademarks are the property of their respective owners.

Summary of content (16 pages)

PAGE 1
LOG101 LOG 101 SBOS242B – MAY 2002 – REVISED JUNE 2004 Precision LOGARITHMIC AND LOG RATIO AMPLIFIER FEATURES DESCRIPTION ● EASY-TO-USE COMPLETE CORE FUNCTION The LOG101 is a versatile integrated circuit that computes the logarithm or log ratio of an input current relative to a reference current. ● HIGH ACCURACY: 0.01% FSO Over 5 Decades ● WIDE INPUT DYNAMIC RANGE: 7.5 Decades, 100pA to 3.5mA ● LOW QUIESCENT CURRENT: 1mA The LOG101 is tested over a wide dynamic range of input signals.
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ELECTROSTATIC DISCHARGE SENSITIVITY ABSOLUTE MAXIMUM RATINGS(1) Supply Voltage, V+ to V– .................................................................... 36V Input Voltage .................................................... (V–) – 0.5 to (V+) + 0.5V Input Current ................................................................................... ±10mA This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions.
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ELECTRICAL CHARACTERISTICS (Cont.) Boldface limits apply over the specified temperature range, TA = –5°C to +75°C. At TA = +25°C, VS = ±5V, and RL = 10kΩ, unless otherwise noted. LOG101AID PARAMETER TOTAL Initial ERROR(4)(5) vs Temperature vs Supply CONDITION MIN MAX UNITS ±75 ±20 ±20 ±20 ±20 ±20 ±20 ±20 ±20 ±20 ±3.0 ±0.1 ±0.1 ±0.1 ±0.1 ±0.1 ±0.1 ±0.25 ±0.1 ±0.
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TYPICAL CHARACTERISTICS At TA = +25°C, VS = ±5V, and RL = 10kΩ, unless otherwise noted. ONE CYCLE OF NORMALIZED TRANSFER FUNCTION NORMALIZED TRANSFER FUNCTION 4.0 VOUT = 1V LOG (I1/I2) Normalized Output Voltage (V) Normalized Output Voltage (V) 3.0 1 2.0 1.0 0.0 –1.0 –2.0 –3.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 –4.0 0.0001 0.001 0.01 0.1 1 10 100 1k 1 10k 2 Current Ratio, I1/I2 6 4 10 8 Current Ratio, I1/I2 TOTAL ERROR vs INPUT CURRENT 120 3 GAIN ERROR (I2 = 1µA) 5.
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TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VS = ±5V, and RL = 10kΩ, unless otherwise noted.
PAGE 6
SETTING THE REFERENCE CURRENT V+ V+ When the LOG101 is used to compute logarithms, either I1 or I2 can be held constant and becomes the reference current to which the other is compared. I1 = 2.5nA to 1mA REF3025 4 2.5V 3 1 VOUT 1GΩ to 2.5kΩ VOUT is expressed as: LOG101 100kΩ I2 = 2.5nA VOUT = (1V) • log (I1/I2) 10MΩ (1) 8 +25mV IREF can be derived from an external current source (such as shown in Figure 3), or it may be derived from a voltage source with one or more resistors.
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V+ +5V TLV271 or 1 OPA2335 2 +3.3V 4 I1 1 1/2 OPA2335 VOUT 10nA to 1mA LOG101 λ 1´ λ1 +5V 1/2 OPA2335 Back Bias D1 Sample 1.5kΩ 1.5kΩ 3 I2 Light λ 1 Source BSH203 +3.3V 10nA to 1mA Pin 1 or Pin 8 8 6 5 D2 CC LOG101 Photodiode V– FIGURE 9. Absorbance Measurement. FIGURE 7. Precision Current Inverter/Current Source. OPERATION ON SINGLE SUPPLY VOLTAGE INPUTS The LOG101 gives the best performance with current inputs.
PAGE 8
INSIDE THE LOG101 also Using the base-emitter voltage relationship of matched bipolar transistors, the LOG101 establishes a logarithmic function of input current ratios. Beginning with the base-emitter voltage defined as: VBE I = VT ln C IS kT where : VT = q VOUT = VL VOUT = (1) k = Boltzman’s constant = 1.381 • 10–23 (9) R1 + R 2 I n VT log 1 R1 I2 VOUT = (1V) • log or T = Absolute temperature in degrees Kelvin R1 + R 2 R1 (10) I1 I2 (11) q = Electron charge = 1.
PAGE 9
to I2 is shown in Figure 13. The OPA703 is configured as a level shifter with inverting gain and is used to scale the photodiode current directly into the A/D converter input voltage range. TOTAL ERROR The total error is the deviation (expressed in mV) of the actual output from the ideal output of VOUT = 1V • log (I1/I2). Thus, VOUT(ACTUAL) = VOUT(IDEAL) ± Total Error. The wide dynamic range of the LOG101 is also useful for measuring avalanche photodiode current (APD) (see Figure 14).
PAGE 10
ISHUNT +15V to +60V 500Ω Irx = 1µA to 1mA Receiver 5kΩ 5kΩ 10Gbits/sec +5V APD INA168 SOT23-5 I to V Converter IOUT = 0.1 • ISHUNT 1 2 IOUT CC 1.2kΩ 1kΩ +5V 4 1 3 Q1 Q2 OPA703 VOUT = 2.5V to 0V A2 A1 100µA 25kΩ 8 LOG101 REF3025 2.5V SO-8 6 5 –5V FIGURE 14. High Side Shunt for Avalanche Photodiode (APD) Measures 3-Decades of APD Current. The individual component of error is: Since the ideal output is 1.000V, the error as a percent of reading is ∆K = gain accuracy (0.
PAGE 11
PACKAGE OPTION ADDENDUM www.ti.
PAGE 12
PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 TAPE AND REEL INFORMATION *All dimensions are nominal Device LOG101AIDR Package Package Pins Type Drawing SOIC D 8 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2500 330.0 12.4 Pack Materials-Page 1 6.4 B0 (mm) K0 (mm) P1 (mm) 5.2 2.1 8.0 W Pin1 (mm) Quadrant 12.
PAGE 13
PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LOG101AIDR SOIC D 8 2500 367.0 367.0 35.
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