High Precision, Wideband RMS-to-DC Converter Data Sheet AD637 FEATURES FUNCTIONAL BLOCK DIAGRAM High accuracy BUFF IN + BUFF OUT 0.02% maximum nonlinearity, 0 V to 2 V rms input 0.1% additional error to crest factor of 3 25k RMS OUT Wide bandwidth SQUARER/ ABSOLUTE V IN DIVIDER VALUE 8 MHz at 2 V rms input 600 kHz at 100 mV rms + Computes 25k DEN INPUT C True rms AV + Square dB OUTPUT OUTPUT Mean square OFFSET BIAS Absolute value COMMON dB output (60 dB range) CS Chip select/power-down feature allows Figure 1. Analog three-state operation Quiescent current reduction from 2.2 mA to 350 A GENERAL DESCRIPTION The AD637 is a complete, high accuracy, rms-to-dc converter facilitates the addition of precision rms measurement to remote that computes the true rms value of any complex waveform. It or handheld applications where minimum power consumption offers performance that is unprecedented in integrated circuit is critical. In addition, when the AD637 is powered down, the rms-to-dc converters and comparable to discrete and modular output goes to a high impedance state. This allows several AD637s to be tied together to form a wideband true rms techniques in accuracy, bandwidth, and dynamic range. The AD637 computes the true root mean square, mean square, or multiplexer. absolute value of any complex ac (or ac plus dc) input waveform The input circuitry of the AD637 is protected from overload and gives an equivalent dc output voltage. The true rms value of voltages in excess of the supply levels. The inputs are not a waveform is more useful than an average rectified signal damaged by input signals if the supply voltages are lost. because it relates directly to the power of the signal. The rms The AD637 is laser wafer trimmed to achieve rated performance value of a statistical signal relates to the standard deviation of without external trimming. The only external component the signal. required is a capacitor that sets the averaging period. The value Superior crest factor compensation permits measurements of this capacitor also determines low frequency accuracy, ripple of signals with crest factors of up to 10 with less than 1% level, and settling time. additional error. The wide bandwidth of the AD637 permits the The on-chip buffer amplifier is used either as an input buffer or measurement of signals up to 600 kHz with inputs of 200 mV rms in an active filter configuration. The filter can be used to reduce and up to 8 MHz when the input levels are above 1 V rms. the amount of ac ripple, thereby increasing accuracy. Direct dB value of the rms output with a range of 60 dB is The AD637 is available in accuracy Grade J and Grade K for available on a separate pin. An externally programmed commercial temperature range (0C to 70C) applications, accuracy reference current allows the user to select the 0 dB reference Grade A and Grade B for industrial range (40C to +85C) appli- voltage to correspond to any level between 0.1 V and 2.0 V rms. cations, and accuracy Grade S rated over the 55C to +125C A chip select connection on the AD637 permits the user to temperature range. All versions are available in hermetically sealed, decrease the supply current from 2.2 mA to 350 A during 14-lead SBDIP, 14-lead CERDIP, and 16-lead SOIC W packages. periods when the rms function is not in use. This feature Rev. L Document Feedback Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 2015 Analog Devices, Inc. All rights reserved. license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. Technical Support www.analog.com 00788-001AD637* PRODUCT PAGE QUICK LINKS Last Content Update: 02/23/2017 COMPARABLE PARTS DESIGN RESOURCES View a parametric search of comparable parts. AD637 Material Declaration PCN-PDN Information EVALUATION KITS Quality And Reliability AD637 Evaluation Board Symbols and Footprints DOCUMENTATION DISCUSSIONS Application Notes View all AD637 EngineerZone Discussions. AN-268: RMS-to-DC Converters Ease Measurement Tasks AN-653: Improving Temperature, Stability, and Linearity SAMPLE AND BUY of High Dynamic Range RMS RF Power Detectors Visit the product page to see pricing options. Data Sheet AD637: High Precision, Wideband RMS-to-DC Converter TECHNICAL SUPPORT Data Sheet Submit a technical question or find your regional support AD637: Military Data Sheet number. Technical Books DOCUMENT FEEDBACK RMS-to-DC Application Guide Second Edition, 1986 Submit feedback for this data sheet. TOOLS AND SIMULATIONS AD637 SPICE Macro Model This page is dynamically generated by Analog Devices, Inc., and inserted into this data sheet. A dynamic change to the content on this page will not trigger a change to either the revision number or the content of the product data sheet. This dynamic page may be frequently modified.