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TL441

LOGARITHMIC AMPLIFIER

SLVS328 – OCTOBER 2000

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Excellent Dynamic Range

Wide Bandwidth

Built-In Temperature Compensation

Log Linearity (30-dB Sections) ...1 dB Typ

Wide Input Voltage Range

description

This amplifier circuit contains four 30-dB

logarithmic stages. Gain in each stage is such that

the output of each stage is proportional to the

logarithm of the input voltage over the 30-dB input

voltage range. Each half of the circuit contains two

of these 30-dB stages summed together in one

differential output that is proportional to the sum of the logarithms of the input voltages of the two stages. The

four stages may be interconnected to obtain a theoretical input voltage range of 120-dB. In practice, this permits

the input voltage range typically to be greater than 80-dB with log linearity of ± 0.5-dB (see application data).

Bandwidth is from dc to 40 MHz.

This circuit is useful in data compression and analog compensation. This logarithmic amplifier is used in log IF

circuitry as well as video and log amplifiers.

The TL441 is characterized for operation over 0°C to 70°C.

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.

–

A2′

B2′

GND

N PACKAGE

(TOP VIEW)

NC — No internal connection

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.

Summary of content (20 pages)

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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 D D D D D N PACKAGE (TOP VIEW) Excellent Dynamic Range Wide Bandwidth Built-In Temperature Compensation Log Linearity (30-dB Sections) . . . 1 dB Typ Wide Input Voltage Range CA2 VCC – CA2′ A1 Y Y A2 VCC + description 1 16 2 15 3 14 4 13 5 12 6 11 NC CB2 CB2′ GND B1 Z Z B2 This amplifier circuit contains four 30-dB 10 7 logarithmic stages.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 functional logic diagram (one half) A1 (B1) Log Σ –15 dB Log Y (Z) Log Y (Z) CA2 (CB2) A2 (B2) –15 dB Log CA2′ (CB2′) Y ∝ log A1 + log A2; Z ∝ log B1 + log B2 where: A1, A2, B1, and B2 are in dBV, 0 dBV = 1 V. CA2, CA2′, CB2, and CB2′ are detector compensation inputs.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 absolute maximum ratings over operating free-air temperature range (unless otherwise noted)† Supply voltages (see Note 1): VCC+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 V VCC – . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . – 8 V Input voltage (see Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 PARAMETER MEASUREMENT INFORMATION VCC+ ICC + VCC– VCC+ VCC– ICC – CA2 CA2′ VCC+ VCC– Y A1 CA2 CA2′ VCC + VCC – Y A1 A2 B1 Y B2 Z DVM Z Y A2 B1 Z B2 Z CB2 CB2′ GND CB2 CB2′ GND VO PD = VCC+ Figure 1 4 • ICC+ + VCC– Figure 2 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 • ICC–
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 PARAMETER MEASUREMENT INFORMATION VCC+ VCC– CA2 CA2′ VCC+ VCC– Y A1 Y A2 B1 Z B2 18 mV 100 mV 560 mV Error ƪ ƪ + + V Z CB2 CB2′ GND DC Power Supply Scale Factor DVM ƫ –V mV out(560 mV) out(18mV) 30 dBV –0.5 V –0.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 TYPICAL CHARACTERISTICS† QUIESCENT OUTPUT VOLTAGE vs FREE-AIR TEMPERATURE DIFFERENTIAL OUTPUT OFFSET VOLTAGE vs FREE-AIR TEMPERATURE 8 7 50 Quiescent Output Voltage – V Differential Output Offset Voltage – mV 60 40 30 20 10 VCC ± = ± 6 V See Figure 1 0 – 75 – 50 – 25 6 5 4 3 2 1 0 25 50 75 100 0 – 75 – 50 – 25 125 Figure 5 DC Error at Midpoint of 30-dBV Range – dBV DC Scale Factor (Differential Output) – mV/dBV 10 8 6 4 VCC ± = ±
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 TYPICAL CHARACTERISTICS OUTPUT RISE TIME vs LOAD CAPACITANCE t r – Output Rise Time – ns 25 20 15 10 VCC ± = ± 6 V TA = 25°C See Figure 4, outputs loaded symmetrically 5 0 0 5 10 15 20 25 CL – Load Capacitance – pF 30 Figure 9 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 7
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 APPLICATION INFORMATION Although designed for high-performance applications such as infrared detection, this device has a wide range of applications in data compression and analog computation. basic logarithmic function functional block diagram The basic logarithmic response is derived from the exponential current-voltage relationship of collector current and base-emitter voltage.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 APPLICATION INFORMATION output levels Differential-output-voltage levels are low, generally less than 0.6 V. As demonstrated in Figure 12, the output swing and the slope of the output response can be adjusted by varying the gain by means of the slope control. The coordinate origin also can be adjusted by positioning the offset of the output buffer. circuits Figures 12 through 19 show typical circuits using this logarithmic amplifier.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 APPLICATION INFORMATION TRANSFER CHARACTERISTICS OF TWO TYPICAL INPUT STAGES 0.4 Output Voltage – V 0.3 0.2 0.1 0 0.001 1 0.1 0.01 10 Input Voltage – V 2 kΩ, 1% B1 2 kΩ, 1% Z 20 kΩ 1/2 TL441 + – Output 2 kΩ, 1% Input B2 GND Z 2 kΩ, 1% Figure 13.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 APPLICATION INFORMATION TRANSFER CHARACTERISTICS WITH BOTH SIDES PARALLELED 0.4 Output Voltage – V 0.3 0.2 0.1 0 0.001 0.01 1 0.1 10 Input Voltage – V 2 kΩ, 1% A1 Y A2 20 kΩ TL441 Input 2 kΩ, 1% Y – Z B1 + Output 2 kΩ, 1% B2 GND Z 2 kΩ, 1% Figure 14.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 APPLICATION INFORMATION TRANSFER CHARACTERISTICS 0.8 0.7 Output Voltage – V 0.6 0.5 0.4 0.3 0.2 0.1 0 10 – 4 10 –3 10 –2 10 –1 1 101 Input Voltage – V 2 kΩ A1 Y A2 Y VCC + = 4 V 1 kΩ 15 kΩ + – VCC – = – 4 V 5 kΩ 1 kΩ 20 kΩ 910 Ω B1 Z B2 Z + – VCC + = 4 V 2 kΩ + – 100 Ω Origin TL441 910 Ω Input 2 kΩ Slope 5 kΩ VCC – = – 4 V 5 kΩ 100 Ω NOTES: A.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 APPLICATION INFORMATION R A1 Y TL441 A2 + Input A – R R R R + Y see Note A + – R B1 + B2 – Y 1/2 TL441 A2 Y + – Z Input B OUTPUT W (see Note B) A1 – Z R R R R NOTES: A. Connections shown are for multiplication. For division, Z and Z connections are reversed. B. Output W may need to be amplified to give actual product or quotient of A and B. C. R designates resistors of equal value, typically 2 kΩ to 10 kΩ.
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TL441 LOGARITHMIC AMPLIFIER SLVS328 – OCTOBER 2000 APPLICATION INFORMATION 2 kΩ Input A 2 kΩ Slope Origin – A1 + 20 kΩ + A2 1/2 TL441 Y Output W Y – 2 kΩ 2 kΩ NOTE: Adjust the slope to correspond to the base “a”. Exponential to any base: W = a. Figure 18. Raising a Fixed Number to a Variable Power 2.2 kΩ A1 Input 1 TL592 0.2 µF 50 Ω 0.2 µF 0.2 µF 50 Ω Output 1 1 kΩ 1 kΩ Gain Adj. 2.2 kΩ Z 20 kΩ B2 Open + – TL441 B1 + – 0.2 µF 2.2 kΩ 50 Ω TL592 TL592 Y Gain Adj.
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE MATERIALS INFORMATION www.ti.com 11-Mar-2008 TAPE AND REEL INFORMATION *All dimensions are nominal Device TL441CNSR Package Package Pins Type Drawing SO NS 16 SPQ Reel Reel Diameter Width (mm) W1 (mm) 2000 330.0 16.4 Pack Materials-Page 1 A0 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 8.2 10.5 2.5 12.0 16.
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PACKAGE MATERIALS INFORMATION www.ti.com 11-Mar-2008 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) TL441CNSR SO NS 16 2000 346.0 346.0 33.
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