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AD640:  120 MHz, 50 dB Demodulating Logarithmic Amplifier

Product Details

The AD640 is a complete monolithic logarithmic amplifier. A single AD640 provides up to 50 dB of dynamic range for frequencies from dc to 120 MHz. Two AD640s in cascade can provide up to 95 dB of dynamic range at reduced bandwidth. The AD640 uses a successive detection scheme to provide an output current proportional to the logarithm of the input voltage. It is laser calibrated to close tolerances and maintains high accuracy over the full military temperature range using supply voltages from ±4.5 V to ±7.5 V.

The AD640 comprises five cascaded dc coupled amplifier/limiter stages, each having a small signal voltage gain of 10 dB and a -3 dB bandwidth of 350 MHz. Each stage has an associated full-wave detector, whose output current depends on the absolute value of its input voltage. The five outputs are summed to provide the video output (when low-pass filtered) scaled at 1 mA per decade (50 µA per dB). On chip resistors can be used to convert this output current to a voltage with several convenient slope options. A balanced signal output at +50 dB (referred to input) is provided to operate AD640s in cascade.

The logarithmic response is absolutely calibrated to within ±l dB for dc or square wave inputs from ±0.75 mV to ±200 mV,with an intercept (logarithmic offset) at 1 mV dc. An integral X10 attenuator provides an alternative input range of ±7.5 mV to ±2 V dc. Scaling is also guaranteed for sinusoidal inputs.

The AD640B is specified for the industrial temperature range of -40°C to +85°C and the AD640T, available processed to MIL-STD- 883B, for the military range of -55°C to +125°C. Both are available in 20-pin side brazed ceramic DIPs or leadless chip carriers (LCC). The AD640J is specified for the commercial temperature range of 0°C to +70°C, and is available in both 20-pin plastic DIP (N) and PLCC (P) packages.

This device is now available to Standard Military Drawing (DESC) number 5962-9095501MRA and 5962-9095501M2A.

An evaluation board is available for this product and may be ordered using the following product number: AD640-EB.


  • Radar, Sonar, Ultrasonic and Audio Systems
  • Precision Instrumentation from DC to 120 MHz
  • Power Measurement with Absolute Calibration
  • Wide Range High Accuracy Signal Compression
  • Alternative to Discrete and Hybrid IF Strips
  • Replaces Several Discrete Log Amp ICs

    • Complete, Fully Calibrated Monolithic System
    • Five Stages, Each Having 10 dB Gain,
      350 MHz BW
    • Direct Coupled Fully Differential Signal Path
    • Logarithmic Slope, Intercept and AC Response are Stable Over Full Military Temperature Range
    • Dual Polarity Current Outputs Scaled
      1 mA/Decade
    • Voltage Slope Operation (1 V/Decade,
      100 mV/dB, etc.)
    • Low Power Operation (Typically 220 mW at
      ±5 V)
    • Low Cost Plastic Packages Also Available

    Functional Block Diagram for AD640


    Title Content Type File Type
    AD640: DC-Coupled Demodulating 120 MHz Logarithmic Amplifier Data Sheet (Rev C, 12/1999) (pdf, 278 kB) Data Sheets PDF
    AD640: Military Data Sheet  (Rev B, 06/2006) (pdf) Data Sheets PDF
    ADI Warns Against Misuse of COTS Integrated Circuits  (pdf, 13 kB)
    (Revised 1/03)
    Invites Customer Participation in Creative Mil/Aero System Solutions
    Recommended Reading PDF
    Measurement and Control of RF Power
    by Eamon Nash, Analog Devices, Inc.
    Technical Articles HTML
    Detecting Fast RF Bursts using Log Amps  (pdf, 174 kB)
    by Yuping Toh, Analog Devices, Inc.
    Technical Articles PDF
    Make Precise Base-Station Power Measurements  (pdf, 1764 kB)
    (Microwaves and RF, November 2002)
    Technical Articles PDF
    Log Amps and Directional Couplers Enable VSWR Detection  (pdf, 2223 kB)
    by Anil Rachakonda and Larry Hawkins, Analog Devices, Inc. (RF Design, 1/1/2007)
    Technical Articles PDF
    Measuring VSWR and Gain in Wireless Systems  (pdf)
    By Eamon Nash, Analog Devices Inc., (Microwave Journal, Nov 2005)
    Technical Articles PDF
    Measuring the RF Power in CDMA2000 and W-CDMA High Power Amplifiers (HPAs)  (pdf, 609 kB)
    By Larry Hawkins, Analog Devices, Inc. (MPD Digest, Nov. 2005)
    Technical Articles PDF
    Design a Logamp RF Pulse Detector  (pdf, 338 kB)
    by Eamon Nash
    (Microwaves & RF, January 1, 2000)
    Technical Articles PDF
    Detecting Fast RF Bursts Using Log Amps
    (Analog Dialogue, Vol. 36, No. 5, September-October, 2002)
    Analog Dialogue HTML
    Choosing High-Speed Signal Processing Components for Ultrasound Systems
    (Analog Dialogue, Vol. 29, No. 2, 1995)
    Analog Dialogue HTML
    Accurate Gain/Phase Measurement at Radio Frequencies up to 2.5 GHz
    (Analog Dialogue, Vol. 35, No. 5, October, 2001)
    Analog Dialogue HTML
    Ask The Applications Engineer - 28
    Logarithmic Amplifiers-Explained

    (Analog Dialogue, Vol. 33, No. 3, March, 1999)
    Analog Dialogue HTML
    Space Qualified Parts List  (pdf, 93 kB)
    This document lists 67 (240+) space level products that are available from Analog Devices. Many of the products listed are state-of-the-art data conversion and signal processing products that were previously only available as commercial or military Class B products. Through our Space Products Group and MIL-PRF-38535 certified Level V (Class S) facility, we are pleased to offer these products to the space marketplace.
    Aerospace Information PDF
    RF Source Booklet  (PDF, 4353 kB)
    RF IC Product Overview - Version P (02/2014)
    Overview PDF
    Industrial Applications Overview HTML
    What is an RF Detector, and how is it used? FAQs/RAQs HTML
    RAQs index Rarely Asked Questions HTML
    Glossary of EE Terms Glossary HTML

    Design Tools,Models,Drivers & Software

    Title Content Type File Type
    ADI’s ADIsimRF design tool provides calculations for the most important parameters within the RF signal chain, including cascaded gain, noise figure, IP3, P1dB, and total power consumption.
    ADIsim Design/Simulation Tools HTML
    ADIsimPLL™- Version 3.60.10
    ADIsimPLL enables the rapid and reliable evaluation of new high performance PLL products from ADI. It is the most comprehensive PLL Synthesizer design and simulation tool available today. Simulations performed include all key non-linear effects that are significant in affecting PLL performance. ADIsimPLL removes at least one iteration from the design process, thereby speeding the design- to-market.
    ADIsim Design/Simulation Tools HTML

    Evaluation Kits & Symbols & Footprints

    Symbols and Footprints— Analog Devices offers Symbols & Footprints which are compatible with a large set of today’s CAD systems for broader and easier support.

    SampleSample & Buy

    Price, packaging, availability

    AD640 Model Options
    Model Package Pins Temp.
    Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
    5962-9095501M2A Status: Production 20 ld LCC 20 Mil Tube, 54 $421.60 $381.14 N  Material Info PCN Purchase
    5962-9095501MRA Status: Production 20 ld Side-Brazed CerDIP 20 Mil Tube, 19 $429.69 $388.43 N  Material Info PCN Purchase
    AD640BD Status: Last Time Buy 20 ld Side-Brazed CerDIP 20 Ind Tube, 19 - - N  Material Info PCN Purchase
    AD640BE Status: Production 20 ld LCC 20 Ind Tube, 54 $132.13 $119.44 Y  Material Info PCN Purchase
    AD640BP Status: Production 20 ld PLCC 20 Ind Tube, 49 $98.57 $89.11 N  Material Info PCN Purchase
    AD640BPZ Status: Production 20 ld PLCC 20 Ind Tube, 49 $89.79 $81.17 Y  Material Info Notify Me Purchase
    AD640JN Status: Last Time Buy 20 ld PDIP 20 Comm. Tube, 18 - - N  Material Info PCN Purchase
    AD640JNZ Status: Production 22 ld PDIP 20 Comm. Tube, 18 $40.36 $36.48 Y  Material Info PCN Purchase
    AD640JP Status: Production 20 ld PLCC 20 Comm. Tube, 49 $44.30 $40.05 N  Material Info PCN Purchase
    AD640JPZ Status: Production 20 ld PLCC 20 Comm. Tube, 49 $40.36 $36.48 Y  Material Info Notify Me Purchase
    AD640JPZ-REEL7 Status: Production 20 ld PLCC 20 Comm. Reel, 250 $40.36 $36.48 Y  Material Info Notify Me Purchase
    AD640TCHIPS Status: Production CHIPS OR DIE 0 Mil Tray, 49 $120.59 $110.73 Y  Material Info Notify Me Purchase
    AD640TD/883B Status: Production 20 ld Side-Brazed CerDIP 20 Mil Tube, 19 $390.62 $353.13 N  Material Info PCN Purchase
    AD640TE/883B Status: Production 20 ld LCC 20 Mil Tube, 54 $382.68 $345.94 N  Material Info PCN Purchase
    Price Table Help

    The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.

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