SBOS246D – JUNE 2002 – REVISED APRIL 2005 …

1 LOG112 LOG2112 SBOS246D JUNE 2002 REVISED APRIL LOG112 and LOG2112 are versatile integrated circuitsthat compute the logarithm or log ratio of an input currentrelative to a reference current. VLOGOUT of the LOG112 andLOG2112 are trimmed to per decade of input current,ensuring high precision over a wide dynamic range of LOG112 and LOG2112 features a voltage refer-ence that may be used to generate a precision currentreference using an external DC offset voltage and temperature drift allow accuratemeasurement of low-level signals over the specified tem-perature range of 5 C to +75 EASY-TO-USE COMPLETE FUNCTION OUTPUT SCALING AMPLIFIER ON-CHIP VOLTAGE REFERENCE HIGH ACCURACY: FSO Over 5 Decades WIDE INPUT DYNAMIC Decades, 100pA to LOW QUIESCENT CURRENT: WIDE SUPPLY RANGE: to 18V PACKAGES: SO-14 (narrow) and SO-16 PRODUCTION DATA information is current as of publication conform to specifications per the terms of Texas Instrumentsstandard warranty.

2 Production processing does not necessarily includetesting of all 2002-2005, Texas Instruments IncorporatedPrecisionLOGARITHMIC AND LOG RATIO AMPLIFIERSP lease be aware that an important notice concerning availability, standard warranty, and use in critical applications ofTexas Instruments semiconductor products and disclaimers thereto appears at the end of this data LOG, LOG RATIO:Communication, Analytical, Medical, Industrial,Test, General Instrumentation PHOTODIODE SIGNAL COMPRESSION AMP ANALOG SIGNAL COMPRESSION IN FRONTOF ANALOG-TO-DIGITAL (A/D) CONVERTER ABSORBANCE MEASUREMENT OPTICAL DENSITY MEASUREMENTLOG112 LOG2112A2A1Q1Q2 CCI1 VREF GNDNOTE: Internal resistors are used to compensate gain change over VCM pin is internally connected to GND in the +GNDLOG112 VLOGOUT = ( )LOG (I1/I2)VO3 = K ( )LOG (I1/I2), K = 1 + R2/R1A3R2R1 VREFRREF+IN3 VLOGOUT IN3V VCMI2 VREFAll trademarks are the property of their respective , MAXIMUM RATINGS(1)Supply Voltage, V+ to V.

3 18 VInputs .. 18 VInput Current .. 10mAOutput Short-Circuit Current(2).. ContinuousOperating Temperature .. 40 C to +85 CStorage Temperature .. 55 C to +125 CJunction Temperature .. +150 CLead Temperature (soldering, 10s) .. +300 CNOTES: (1) Stresses above these ratings may cause permanent to absolute maximum conditions for extended periods may degradedevice reliability. (2) One output per CONFIGURATIONTop ViewSOI2 VCM INNCVREF GNDGNDV VREFNC = No Internal ConnectionLOG112I1NC+IN3 IN3 VLOGOUTV+VO31413121110981234567I1BI2B+IN 3B IN3 BVLOGOUTBV V03 BVREFLOG2112I1AI2A+IN3A IN3 AVLOGOUTAV+VO3 AGND16151413121110912345678 ELECTROSTATICDISCHARGE SENSITIVITYThis integrated circuit can be damaged by ESD. Texas Instru-ments recommends that all integrated circuits be handled withappropriate precautions. Failure to observe proper handlingand installation procedures can cause damage can range from subtle performance degradationto complete device failure.

4 Precision integrated circuits may bemore susceptible to damage because very small parametricchanges could cause the device not to meet its -14 DLOG112 ALOG2112SO -16 DWLOG2112 ANOTES: (1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI website INFORMATION(1)LOG112, CHARACTERISTICSB oldface limits apply over the specified temperature range, TA = 5 C to +75 TA = +25 C, VS = 5V, and ROUT = 10k , unless otherwise , LOG2112 PARAMETERCONDITIONMINTYPMAXUNITSCORE LOG FUNCTIONVIN/VOUT EquationVLOGOUT = ( )LOG (I1/I2)VLOG CONFORMITY ERROR(1)Initial1nA to 100 A (5 decades) to ( decades) Temperature1nA to 100 A (5 decades) C100pA to ( decades) CGAIN(2)Initial Value1nA to 100 Error1nA to 100 1%vs TemperatureTMIN to / CINPUT, A1A and A1B, A2A, A2 BOffset Voltage TemperatureTMIN to TMAX 2 V/ Cvs Power Supply (PSRR)

5 VS = to 18V520 V/VInput Bias Current 5pAvs TemperatureTMIN to TMAXD oubles Every 10 CVoltage Noisef = 10Hz to 10kHz3 Vrmsf = 1kHz30nV/ HzCurrent Noisef = 1kHz4fA/ HzCommon-Mode Voltage Range (Positive)(V+) 2(V+) (Negative)(V ) + 2(V ) + Rejection Ratio (CMRR)10 V/VOUTPUT, (VLOG OUT) A2A, A2 BOutput Offset, VOSO, Initial 3 15mVvs TemperatureTMIN to TMAX 10 V/ CFull-Scale Output (FSO)VS = 5V(V ) + (V+) Current 18mATOTAL ERROR(3)(4)I1 or I2 remains fixed while other to MaxI1 or I2 = 5mA (VS 6V) 150mVI1 or I2 = 75mVI1 or I2 = 1mA 20mVI1 or I2 = 100 A 20mVI1 or I2 = 10 A 20mVI1 or I2 = 1 A 20mVI1 or I2 = 100nA 20mVI1 or I2 = 10nA 20mVI1 or I2 = 1nA 20mVI1 or I2 = 350pA 20mVI1 or I2 = 100pA 20mVvs TemperatureI1 or I2 = CI1 or I2 = 1mA CI1 or I2 = 100 A CI1 or I2 = 10 A CI1 or I2 = 1 A CI1 or I2 = 100nA CI1 or I2 = 10nA CI1 or I2 = 1nA CI1 or I2 = 350pA CI1 or I2 = 100pA Cvs SupplyI1 or I2 = VI1 or I2 = 1mA VI1 or I2 = 100 A VI1 or I2 = 10 A VI1 or I2 = 1 A VI1 or I2 = 100nA VI1 or I2 = 10nA VI1 or I2 = 1nA or I2 = 350pA VI1 or I2 = 100pA VNOTES: (1) Log Conformity Error is the peak deviation from the best-fit-straight line of VO versus LOG (I1/I2) curve expressed as a percent of peak-to-peak full-scale output.

6 K, scale factor, equals output per decade of input current. (2) Scale factor of core log function is trimmed to output per decade change ofinput current. (3) Worst-case Total Error for any ratio of I1/I2, as the largest of the two errors, when I1 and I2 are considered separately. (4) Total Error includes offsetvoltage, bias current, gain, and log conformity. (5) Bandwidth (3dB) and transient response are a function of both the compensation capacitor and the level of , RESPONSE, CORE LOG(5)BW, 3dBI2 = 10nACC = = 1 ACC = 150pF38kHI2 = 10 ACC = 150pF40kHI2 = 1mACC = 50pF45kHzStep ResponseIncreasingI1 = 10nA to 100nACC = 120pF, I2 = = 1 A to 100 ACC = 375pF, I2 = 10 sI1 = 1 A to 1mACC = 950pF, I2 = sDecreasingI1 = 100nA to 10nACC = 120pF, I2 = = 100 A to 1 ACC = 375pF, I2 = 10 sI1 = 1mA to 1 ACC = 950pF, I2 = A39 sIncreasingI2 = 10nA to 100nACC = 125pF, I1 = = 1 A to 100 ACC = 750pF, I1 = 10 A113 sI2 = 1 A to 1mACC = , I1 = = 100nA to 10nACC = 125pF, I1 = sI2 = 100 A to 1 ACC = 750pF, I1 = 10 sI2 = 1mA to 1 ACC = , I1 = sOP AMP, A3 Input Offset Voltage+250 1000 Vvs TemperatureTMIN to TMAX 2 V/ Cvs SupplyVS = to 18V550 V/VInput Bias Current 10nAInput Offset Current Voltage Range(V )(V+)

7 Noise, f = to 10Hz1 VPP f = 1kHz28nV/ HzOpen-Loop Voltage Gain88dBGain-Bandwidth sSettling Time, = 1, 3V Step, CL = 100pF16 sRated Output(V ) + (V+) Current 4mAVOLTAGE REFERENCEB andgap , Initial TemperatureTMIN to TMAX 25ppm/ Cvs SupplyVS = to 18V 10ppm/Vvs LoadILOAD = 10mA 600ppm/mAShort-Circuit Current16mAPOWER SUPPLYO perating RangeVS 18 VQuiescent CurrentIO = 0 LOG112 RANGES pecified Range, TMIN to TMAX 575 COperating Range 4085 CStorage Range 55125 CThermal Resistance, JA SO-14110 C/WSO-1680 C/WNOTES: (1) Log Conformity Error is the peak deviation from the best-fit-straight line of VO vs LOG(I1/I2) curve expressed as a percent of peak-to-peak full-scaleoutput. K, scale factor, equals output per decade of input current. (2) Scale factor of core log function is trimmed to output per decade change of inputcurrent. (3) Worst-case Total Error for any ratio of I1/I2, as the largest of the two errors, when I1 and I2 are considered separately.

8 (4) Total Error includes offsetvoltage, bias current, gain, and log conformity. (5) Bandwidth (3dB) and transient response are a function of both the compensation capacitor and the level of CHARACTERISTICS (Cont.)Boldface limits apply over the specified temperature range, TA = 5 C to +75 TA = +25 C, VS = 5V, and RL = 10k , unless otherwise , LOG2112 PARAMETERCONDITIONMINTYPMAXUNITSLOG112, CHARACTERISTICSAt TA = +25 C, VS = 5V, and RL = 10k , unless otherwise Output Voltage (V)NORMALIZED TRANSFER Ratio, I1/I2 VLOGOUT = ( )LOG (I1/I2)ONE CYCLE OF NORMALIZED TRANSFER FUNCTIONN ormalized Output Voltage (V) Ratio, I1/I2 876543210 1 21nA10nA 100nA 1 A10 A 100 A 1mA 10mA100pAGAIN ERROR (I2 = 1 A)Input Current (I1 or I2)Gain Error (%) 40 C+75 C 5 C+25 C+85 C 20 15 10 505101520 20 15 10 5051015201mA10 A100nA1nA10nA100nA1 A10 A100 A1mA1nAI1I2 Total Error (mV)TOTAL ERROR ( 5 C)Total Error (mV)10 to 155 to 100 to 5 5 to 0 20 15 10 505101520 20 15 10 5051015201mA10 A100 A1 A100nA1nA10nA100nA1 A10 A100 A1mA10nA1nAI1I2 Total Error (mV)Total Error (mV)5 to 100 to 5 5 to 0 TOTAL ERROR (25 C)

9 20200406080100 200204060801001mA10 A100 A1 A100nA1nA10nA100nA1 A10 A100 A1mA10nA1nAI1I2 Total Error (mV)Total Error (mV)20 to 400 to 2040 to 6060 to 8080 to 100 20 to 0 TOTAL ERROR (70 C)LOG112, CHARACTERISTICS (Cont.)At TA = +25 C, VS = 5V, and RL = 10k , unless otherwise VALUE OF COMPENSATION CAPACITOR100M10M1M100k10k1k100101CC (pF)100pA1nA10nA 100nA 1 A10 A 100 A 1mA 10mAI2I1 = 100pAI1 = 1nAI1 = 10nAI1 = 100nA1 AI1 = 10 A100 A1mASelect CC for I1 I2 max. Values below 2pF may be FREQUENCY RESPONSE3dB Frequency Response (Hz) A100 A1mAI1 = 1mA1 A1mA to 10 A100nA10nAI1 = 1nA10nACC = 1000pFCC = 1 F10 A to 1 ACC = 10pF1nA100 A100pA1nA10nA100nA1 A10 A100 A1mAI21 A10 A100 AI1 = 1nA10nA1715131197531 1 Input Current (I1 or I2)Log Conformity (mV)LOG CONFORMITY vs INPUT CURRENT+85 C+75 C 40 C to +25 C100pA1nA10nA 100nA1 A10 A 100 A1mALOG CONFORMITY vs TEMPERATURELog Conformity (m%)7006005004003002001000 40 20020406080 Temperature ( C) Decade7 Decade6 Decade5 DecadeLOG112, 1.

10 Basic Connections of the INFORMATIONThe LOG112 is a true logarithmic amplifier that uses thebase-emitter voltage relationship of bipolar transistors tocompute the logarithm, or logarithmic ratio of a current 1 and Figure 2 show the basic connections requiredfor operation of the LOG112 and LOG2112. In order toreduce the influence of lead inductance of power-supplylines, it is recommended that each supply be bypassed witha 10 F tantalum capacitor in parallel with a 1000pF ceramiccapacitor, as shown in Figure 1 and Figure 2. Connectingthe capacitors as close to the LOG112 and LOG2112 aspossible will contribute to noise reduction as CURRENT RANGETo maintain specified accuracy, the input current range of theLOG112 and LOG2112 should be limited from 100pA Input currents outside of this range may compromisethe LOG112 performance. Input currents larger than in increased nonlinearity.