Image AD637
型号: AD637
厂商: Analog Devices Inc Analog Devices Inc
分类: 半导体
描述: high precision, wide-band rms-to-DC converter
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High Precision,  
a
Wide-Band RMS-to-DC Converter  
AD637  
FUNCTIONAL BLOCK DIAGRAMS  
FEATURES  
High Accuracy  
Ceramic DIP (D) and  
SOIC (R) Package  
0.02% Max Nonlinearity, 0 V to 2 V RMS Input  
0.10% 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 “3-State” Operation  
Quiescent Current Reduction from 2.2 mA to 350 A  
Side-Brazed DIP, Low Cost Cerdip and SOIC  
Cerdip (Q) Packages  
BUFFER  
AD637  
BUFFER  
AD637  
1
2
3
4
5
6
7
8
16  
15  
14  
13  
12  
11  
10  
9
1
2
3
4
5
6
7
14  
13  
12  
11  
10  
9
ABSOLUTE  
VALUE  
ABSOLUTE  
VALUE  
BIAS  
SECTION  
BIAS  
SQUARER/DIVIDER  
SECTION  
SQUARER/DIVIDER  
25k  
25k⍀  
25k⍀  
25k⍀  
FILTER  
FILTER  
8
PRODUCT DESCRIPTION  
The AD637 is available in two accuracy grades (J, K) for com-  
mercial (0°C to +70°C) temperature range applications; two  
accuracy grades (A, B) for industrial (–40°C to +85°C) applica-  
tions; and one (S) rated over the –55°C to +125°C temperature  
range. All versions are available in hermetically-sealed, 14-lead  
side-brazed ceramic DIPs as well as low cost cerdip packages. A  
16-lead SOIC package is also available.  
The AD637 is a complete high accuracy monolithic rms-to-dc  
converter that computes the true rms value of any complex  
waveform. It offers performance that is unprecedented in inte-  
grated circuit rms-to-dc converters and comparable to discrete  
and modular techniques in accuracy, bandwidth and dynamic  
range. A crest factor compensation scheme in the AD637 per-  
mits measurements of signals with crest factors of up to 10 with  
less than 1% additional error. The circuit’s wide bandwidth per-  
mits 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.  
PRODUCT HIGHLIGHTS  
1. 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 since it relates directly to the power of  
the signal. The rms value of a statistical signal is also related  
to the standard deviation of the signal.  
As with previous monolithic rms converters from Analog Devices,  
the AD637 has an auxiliary dB output available to the user. The  
logarithm of the rms output signal is brought out to a separate  
pin allowing direct dB measurement with a useful range of  
60 dB. 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.  
2. The AD637 is laser wafer trimmed to achieve rated perfor-  
mance without external trimming. The only external compo-  
nent required is a capacitor which sets the averaging time  
period. The value of this capacitor also determines low fre-  
quency accuracy, ripple level and settling time.  
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 facili-  
tates the addition of precision rms measurement to remote or  
hand-held applications where minimum power consumption is  
critical. In addition when the AD637 is powered down the out-  
put goes to a high impedance state. This allows several AD637s  
to be tied together to form a wide-band true rms multiplexer.  
3. The chip select feature of the AD637 permits the user to  
power down the device down during periods of nonuse,  
thereby, decreasing battery drain in remote or hand-held  
applications.  
4. The on-chip buffer amplifier can be used as either an input  
buffer or in an active filter configuration. The filter can be  
used to reduce the amount of ac ripple, thereby, increasing  
the accuracy of the measurement.  
The input circuitry of the AD637 is protected from overload  
voltages that are in excess of the supply levels. The inputs will  
not be damaged by input signals if the supply voltages are lost.  
REV. E  
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  
which may result from its use. No license is granted by implication or  
otherwise under any patent or patent rights of Analog Devices.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781/329-4700  
Fax: 781/326-8703  
World Wide Web Site: http://www.analog.com  
© Analog Devices, Inc., 1999