Low Level, True RMS-to-DC Converter
Data Sheet
AD636
FEATURES FUNCTIONAL BLOCK DIAGRAM
True rms-to-dc conversion
ABSOLUTE
V
IN
200 mV full scale VALUE
Laser-trimmed to high accuracy
0.5% maximum error (AD636K)
dB
SQUARER
1.0% maximum error (AD636J)
COM
DIVIDER
Wide response capability
C
AV
+V
S
+V
S
Computes rms of ac and dc signals
1 MHz, 3 dB bandwidth: V rms > 100 mV
CURRENT
Signal crest factor of 6 for 0.5% error
MIRROR
dB output with 50 dB range
10k
R
L
Low power: 800 A quiescent current
+V
S
Single or dual supply operation
I
OUT
BUFFER IN
Monolithic integrated circuit
BUF
Low cost
10k
BUFFER OUT
40k
AD636
GENERAL DESCRIPTION
V
S
The AD636 is a low power monolithic IC that performs true
V
S
rms-to-dc conversion on low level signals. It offers performance
Figure 1.
that is comparable or superior to that of hybrid and modular
converters costing much more. The AD636 is specified for a The AD636 is available in two accuracy grades. The total error of the
signal range of 0 mV to 200 mV rms. Crest factors up to 6 can J-version is typically less than 0.5 mV 1.0% of reading, while
be accommodated with less than 0.5% additional error, allowing the total error of the AD636K is less than 0.2 mV to 0.5% of
accurate measurement of complex input waveforms. reading. Both versions are temperature rated for operation
between 0C and 70C and available in 14-lead SBDIP and 10-lead
The low power supply current requirement of the AD636,
TO-100 metal can.
typically 800 A, is ideal for battery-powered portable
instruments. It operates from a wide range of dual and single The AD636 computes the true root-mean-square of a complex ac
power supplies, from 2.5 V to 16.5 V or from +5 V to +24 V. (or ac plus dc) input signal and gives an equivalent dc output level.
The input and output terminals are fully protected; the input 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
signal can exceed the power supply with no damage to the device
(allowing the presence of input signals in the absence of supply in the signal. The rms value of an ac-coupled signal is also its
voltage), and the output buffer amplifier is short-circuit protected. standard deviation.
The AD636 includes an auxiliary dB output derived from an The 200 mV full-scale range of the AD636 is compatible with
internal circuit point that represents the logarithm of the rms many popular display-oriented ADCs. The low power supply
output. The 0 dB reference level is set by an externally supplied current requirement permits use in battery-powered hand-held
current and can be selected to correspond to any input level from instruments. An averaging capacitor is the only external
0 dBm (774.6 mV) to 20 dBm (77.46 mV). Frequency response component required to perform measurements to the fully
ranges from 1.2 MHz at 0 dBm to greater than 10 kHz at 50 dBm. specified accuracy is. Its value optimizes the trade-off between
low frequency accuracy, ripple, and settling time.
The AD636 is easy to use. The device is factory-trimmed at the
wafer level for input and output offset, positive and negative An optional on-chip amplifier acts as a buffer for the input or the
waveform symmetry (dc reversal error), and full-scale accuracy output signals. Used in the input, it provides accurate
at 200 mV rms. Therefore, no external trims are required to performance from standard 10 M input attenuators. As an
achieve full-rated accuracy. output buffer, it sources up to 5 mA.
Rev. E Document Feedback
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Last Content Update: 02/23/2017
COMPARABLE PARTS DESIGN RESOURCES
View a parametric search of comparable parts. AD636 Material Declaration
PCN-PDN Information
DOCUMENTATION
Quality And Reliability
Application Notes
Symbols and Footprints
AN-268: RMS-to-DC Converters Ease Measurement Tasks
DISCUSSIONS
AN-653: Improving Temperature, Stability, and Linearity
of High Dynamic Range RMS RF Power Detectors
View all AD636 EngineerZone Discussions.
Data Sheet
AD636: Low Level, True RMS-to-DC Converter Data Sheet
SAMPLE AND BUY
Technical Books
Visit the product page to see pricing options.
RMS-to-DC Application Guide Second Edition, 1986
TECHNICAL SUPPORT
TOOLS AND SIMULATIONS
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number.
AD636P SPICE Macro Model
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