High Precision, Wideband
RMS-to-DC Converter
Data Sheet
AD637
FEATURES
High accuracy
0.02% maximum nonlinearity, 0 V to 2 V rms input
0.1% additional error to crest factor of 3
Wide bandwidth
8 MHz at 2 V rms input
600 kHz at 100 mV rms
Computes
True rms
Square
Mean square
Absolute value
dB output (60 dB range)
Chip select/power-down feature allows
Analog three-state operation
Quiescent current reduction from 2.2 mA to 350 µA
FUNCTIONAL BLOCK DIAGRAM
00788-001
V
IN
25k
Ω
25k
Ω
ABSOLUTE
VALUE
DEN
INPUT
C
AV
RMS OUT
BUFF IN
BUFF OUT
SQUARER
/
DIVIDER
BIAS
COMMON
CS
OUTPUT
OFFSET
dB OUTPUT
–
+
+
–
–
+
Figure 1.
GENERAL DESCRIPTION
The AD637 is a complete, high accuracy, rms-to-dc converter
that computes the true rms value of any complex waveform. It
offers performance that is unprecedented in integrated circuit
rms-to-dc converters and comparable to discrete and modular
techniques in accuracy, bandwidth, and dynamic range. The
AD637 computes the true root mean square, mean square, or
absolute value of any complex ac (or ac plus dc) input waveform
and gives an equivalent dc output voltage. The true rms value of
a waveform is more useful than an average rectified signal
because it relates directly to the power of the signal. The rms
value of a statistical signal relates to the standard deviation of
the signal.
Superior crest factor compensation permits measurements
of signals with crest factors of up to 10 with less than 1%
additional error. The wide bandwidth of the AD637 permits the
measurement of signals up to 600 kHz with inputs of 200 mV rms
and up to 8 MHz when the input levels are above 1 V rms.
Direct dB value of the rms output with a range of 60 dB is
available on a separate pin. An externally programmed
reference current allows the user to select the 0 dB reference
voltage to correspond to any level between 0.1 V and 2.0 V rms.
A chip select connection on the AD637 permits the user to
decrease the supply current from 2.2 mA to 350 µA during
periods when the rms function is not in use. This feature
facilitates the addition of precision rms measurement to remote
or handheld applications where minimum power consumption
is critical. In addition, when the AD637 is powered down, the
output goes to a high impedance state. This allows several
AD637s to be tied together to form a wideband true rms
multiplexer.
The input circuitry of the AD637 is protected from overload
voltages in excess of the supply levels. The inputs are not
damaged by input signals if the supply voltages are lost.
The AD637 is laser wafer trimmed to achieve rated performance
without external trimming. The only external component
required is a capacitor that sets the averaging period. The value
of this capacitor also determines low frequency accuracy, ripple
level, and settling time.
The on-chip buffer amplifier is used either as an input buffer or
in an active filter configuration. The filter can be used to reduce
the amount of ac ripple, thereby increasing accuracy.
The AD637 is available in accuracy Grade J and Grade K for
commercial temperature range (0°C to 70°C) applications, accuracy
Grade A and Grade B for industrial range (−40°C to +85°C) appli-
cations, and accuracy Grade S rated over the −55°C to +125°C
temperature range. All versions are available in hermetically sealed,
14-lead SBDIP, 14-lead CERDIP, and 16-lead SOIC_W packages.
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
rights of third parties that may result from its use. Specifications subject to change without notice. No
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 ©2015 Analog Devices, Inc. All rights reserved.
Technical Support www.analog.com
评论1