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AD636:  Low Level, True RMS-to-DC Converter

Product Details

The AD636 is a low power monolithic IC that performs true rms-to-dc conversion on low level signals. It offers performance that is comparable or superior to that of hybrid and modular converters costing much more. The AD636 is specified for a signal range of 0 mV to 200 mV rms. Crest factors up to 6 can be accommodated with less than 0.5% additional error, allowing accurate measurement of complex input waveforms.

The low power supply current requirement of the AD636, typically 800 μA, is ideal for battery-powered portable instruments. It operates from a wide range of dual and single power supplies, from ±2.5 V to ±16.5 V or from +5 V to +24 V. The input and output terminals are fully protected; the input signal can exceed the power supply with no damage to the device (allowing the presence of input signals in the absence of supply voltage), and the output buffer amplifier is short-circuit protected.

The AD636 includes an auxiliary dB output derived from an internal circuit point that represents the logarithm of the rms output. The 0 dB reference level is set by an externally supplied current and can be selected to correspond to any input level from 0 dBm (774.6 mV) to −20 dBm (77.46 mV). Frequency response ranges from 1.2 MHz at 0 dBm to greater than 10 kHz at −50 dBm.

The AD636 is easy to use. The device is factory-trimmed at the wafer level for input and output offset, positive and negative waveform symmetry (dc reversal error), and full-scale accuracy at 200 mV rms. Therefore, no external trims are required to achieve full-rated accuracy.

The AD636 is available in two accuracy grades. The total error of the J-version is typically less than ±0.5 mV ± 1.0% of reading, while the total error of the AD636K is less than ±0.2 mV to ±0.5% of reading. Both versions are temperature rated for operation between 0°C and 70°C and available in 14-lead SBDIP and 10-lead TO-100 metal can.

The AD636 computes the true root-mean-square of a complex ac (or ac plus dc) input signal and gives an equivalent dc output level. The true rms value of a waveform is a more useful quantity than the average rectified value because it is a measure of the power in the signal. The rms value of an ac-coupled signal is also its standard deviation.

The 200 mV full-scale range of the AD636 is compatible with many popular display-oriented ADCs. The low power supply current requirement permits use in battery-powered hand-held instruments. An averaging capacitor is the only external component required to perform measurements to the fully specified accuracy is. Its value optimizes the trade-off between low frequency accuracy, ripple, and settling time.

An optional on-chip amplifier acts as a buffer for the input or the output signals. Used in the input, it provides accurate performance from standard 10 MΩ input attenuators. As an output buffer, it sources up to 5 mA.


  • Laser-trimmed to high accuracy
    0.5% maximum error (AD636K)
    1.0% maximum error (AD636J)
  • Wide response capability
    Computes rms of ac and dc signals
    1 MHz, −3 dB bandwidth: V rms > 100 mV
    Signal crest factor of 6 for 0.5% error
  • True rms-to-dc conversion
  • 200 mV full scale
  • dB output with 50 dB range
  • Low power: 800 μA quiescent current
  • Single or dual supply operation
  • Monolithic integrated circuit
  • Low cost

Functional Block Diagram for AD636


Title Content Type File Type
AD636: Low Level, True RMS-to-DC Converter Data Sheet (Rev E, 05/2013) (pdf, 463 kB) Data Sheets PDF
AN-653: Improving Temperature, Stability, and Linearity of High Dynamic Range RMS RF Power Detectors  (pdf, 415 kB) Application Notes PDF
AN-268: RMS-to-DC Converters Ease Measurement Tasks  (pdf, 638 kB)
RMS-to-DC Converters compute the true RMS value of a signal without regard to waveform shape.
Application Notes PDF
RMS-to-DC Application Guide Second Edition Design Handbooks HTML
Introduction to Analog RMS-to-DC Technology: Converters and Applications Online Training Modules HTML
RAQs index Rarely Asked Questions HTML
Glossary of EE Terms Glossary HTML

Design Tools,Models,Drivers & Software

Title Content Type File Type
AD636P SPICE Macro Model SPICE Models 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.

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Price, packaging, availability

AD636 Model Options
Model Package Pins Temp.
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
AD636JDZ Status: Production 14 ld Bottom-Brazed CerDIP 14 Comm. Tube, 25 $22.62 $20.37 Y  Material Info PCN Purchase
AD636JH Status: Production ROUND HEADER/METAL CAN 10 Comm. Tube, 100 $18.99 $17.02 N  Material Info PCN/PDN Purchase
AD636JHZ Status: Production ROUND HEADER/METAL CAN 10 Comm. Tube, 100 $13.23 $11.82 Y  Material Info PCN Purchase
AD636KDZ Status: Production 14 ld Bottom-Brazed CerDIP 14 Comm. Tube, 25 $40.18 $40.18 Y  Material Info PCN Purchase
AD636KH Status: Production ROUND HEADER/METAL CAN 10 Comm. Tube, 100 $26.73 $26.73 N  Material Info PCN/PDN Purchase
AD636KHZ Status: Production ROUND HEADER/METAL CAN 10 Comm. Tube, 100 $18.92 $18.92 Y  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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