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Product Details

The AD641 is a 250 MHz, demodulating logarithmic amplifier with an accuracy of ±2.0 dB and 44 dB dynamic range. The AD641 uses a successive detection architecture to provide an output current that is logarithmically proportional to its input voltage. The output current can be converted to a voltage using one of several on-chip resistors to select the slope. A single AD641 provides up to 44 dB of dynamic range at speeds up to 250 MHz, and two cascaded AD641s together can provide 58 dB of dynamic range at speeds up to 250 MHz. The AD641 is fully stable and well characterized over either the industrial or military temperature ranges.

The AD641 is not a logarithmic building block, but rather a complete logarithmic solution for compressing and measuring dynamic range signals. The AD641 is comprised of five stages and each stage has a full wave rectifier, whose current pends on the absolute value of its input voltage. The output of these stages are summed together to provide the demodulated output current scaled at 1 mA per decade (50 µA/dB).

Without utilizing the 10x input attenuator, log conformance of 2.0 dB is maintained over the input range -44 dBm to 0 dBm. The attenuator offers the most flexibility without significantly impacting performance.

The 250 MHz bandwidth and temperature stability make this product ideal for high speed signal power measurement in RF/IF systems. ECM/Radar and Communication applications are routinely in the 100 MHz-180 MHz range for power measurement. The bandwidth and accuracy, as well as dynamic range, make this part ideal for high speed, wide dynamic range signals.

The AD641 is offered in industrial (-40°C to +85°C) and military (-55°C to +125°C) package temperature ranges. Industrial versions are available in plastic DIP and PLCC; MIL versions are packaged in cerdip.

An evaluation board is available for this product and may be ordered using the following product number: AD641-EB.


  • Logarithmic Amplifier Performance
    Usable to 250 MHz
    44 dB Dynamic Range
    ±2.0 dB Log Conformance
    37.5 mV/dB Voltage Output
    Stable Slope and Intercepts
  • 2.0 nV/vHz Input Noise Voltage
  • 50 µV Input Offset Voltage
  • Low Power
    ±5 V Supply Operation
    9 mA (+Vs), 35 mA (-Vs)
    Quiescent Current
  • Onboard Resistors
  • Onboard 10x Attenuator
  • Dual Polarity Current Outputs
  • Direct Coupled Differential Signal Path

Pin Configuration Diagram for AD641


Title Content Type File Type
AD641: 250 MHz Demodulating Logarithmic Amplifier Data Sheet (Rev C, 08/1999) (pdf, 256 kB) Data Sheets PDF
AD641: Military Data Sheet  (Rev A, 03/1998) (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
Ask The Applications Engineer - 28
Logarithmic Amplifiers-Explained

(Analog Dialogue, Vol. 33, No. 3, March, 1999)
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
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

AD641 Model Options
Model Package Pins Temp.
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
5962-9559801MRA Status: Contact ADI 20 ld CerDIP 20 Mil Tube, 18 $500.00 $500.00 N  Material Info PCN Contact ADI
AD641AN Status: Production 20 ld PDIP 20 Ind Tube, 18 $39.86 $36.04 N  Material Info PCN Purchase
AD641ANZ Status: Production 20 ld PDIP 20 Ind Tube, 18 $36.31 $32.82 Y  Material Info PCN Purchase
AD641AP Status: Production 20 ld PLCC 20 Ind Tube, 49 $39.86 $36.04 N  Material Info PCN Purchase
AD641AP-REEL7 Status: Production 20 ld PLCC 20 Ind Reel, 250 $38.13 $34.46 N  Material Info PCN Purchase
AD641APZ Status: Production 20 ld PLCC 20 Ind Tube, 49 $36.31 $32.82 Y  Material Info Notify Me 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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