ANALOG DEVICES AD636 Service Manual
www.BDTIC.com/ADI
Low Level, True RMS-to-DC Converter
FEATURES
True rms-to-dc conversion
200 mV full scale
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
dB output with 50 dB range
Low power: 800 μA quiescent current
Single or dual supply operation
Monolithic integrated circuit
Low cost
GENERAL DESCRIPTION
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.
AD636
FUNCTIONAL BLOCK DIAGRAM
dB
R
L
I
OUT
BUF OUT
10kΩ
Figure 1.
SQUARER
DIVIDER
CURRENT
MIRROR
10kΩ
+V
S
BUF IN
V
IN
C
AV
ABSOLUTE
VALUE
AD636
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
o
f 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.
00787-001
The low power supply current requirement of the AD636,
ically 800 A, is ideal for battery-powered portable
typ
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
in
ternal 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
wa
fer level for input and output offset, positive and negative
waveform symmetry (dc reversal error), and full-scale accuracy
Rev. D
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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.
The AD636 computes the true root-mean-square of a complex
ac (o
r 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
ma
ny 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
e output signals. Used in the input, it provides accurate
th
performance from standard 10 M input attenuators. As an
output buffer, it sources up to 5 mA.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2006 Analog Devices, Inc. All rights reserved.
AD636
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TABLE OF CONTENTS
Features.............................................................................................. 1
AD636 Principle of Operation................................................9
Functional Block Diagram ..............................................................1
General Description......................................................................... 1
Revision History ...............................................................................2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Pin Configurations and Function Descriptions........................... 6
Applying the AD636......................................................................... 7
Standard Connection................................................................... 7
Optional Trims for High Accuracy............................................ 7
Single-Supply Connection........................................................... 7
Choosing the Averaging Time Constant................................... 8
RMS Measurements..................................................................... 9
REVISION HISTORY
The AD636 Buffer Amplifier.......................................................9
Frequency Response .................................................................. 10
AC Measurement Accuracy and Crest Factor (CF)............... 10
A Complete AC Digital Voltmeter........................................... 11
A Low Power, High Input, Impedance dB Meter....................... 11
Circuit Description................................................................ 11
Performance Data .................................................................. 11
Frequency Response ±3 dBm............................................... 11
Calibration .............................................................................. 11
Outline Dimensions....................................................................... 13
Ordering Guide .......................................................................... 13
11/06—Rev. C to Rev. D
Changes to General Description .................................................... 1
Changes to Table 1............................................................................ 3
Changes to Ordering Guide.......................................................... 13
1/06—Rev B to Rev. C
pdated Format..................................................................Universal
U
Changes to Figure 1 and General Description ............................. 1
Deleted Metalization Photograph.................................................. 3
Added Pin Configuration and Function Description Section.... 6
Updated Outline Dimensions....................................................... 14
Changes to Ordering Guide.......................................................... 14
8/99—Rev A to Rev. B
Rev. D | Page 2 of 16
AD636
(
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SPECIFICATIONS
@ 25°C, +VS = +3 V, and −VS = –5 V, unless otherwise noted.
Table 1.
Model
TRANSFER FUNCTION
CONVERSION ACCURACY
Total Error, Internal Trim
vs. Temperature, 0°C to +70°C ±0.1 ± 0.01 ±0.1 ± 0.005
vs. Supply Voltage ±0.1 ± 0.01 ±0.1 ± 0.01
DC Reversal Error at 200 mV ±0.2 ±0.1 % of reading
Total Error, External Trim2 ±0.3 ± 0.3 ± 0.1 ± 0.2
ERROR VS. CREST FACTOR4
Crest Factor 1 to 2 Specified Accuracy Specified Accuracy
Crest Factor = 3 −0.2 −0.2 % of reading
Crest Factor = 6 −0.5 −0.5 % of reading
AVERAGING TIME CONSTANT 25 25 ms/F of CAV
INPUT CHARACTERISTICS
Signal Range, All Supplies
Continuous RMS Level 0 to 200 0 to 200 mV rms
Peak Transient Inputs
+3 V, −5 V Supply ±2.8 ±2.8 V p-p
±2.5 V Supply ±2.0 ±2.0 V p-p
±5 V Supply ±5.0 ±5.0 V p-p
Maximum Continuous
Nondestructive
Input Level (All Supply Voltages) ±12 ±12 V p-p
Input Resistance 5.33 6.67 8 5.33 6.67 8 kΩ
Input Offset Voltage ±0.5 ±0.2 mV
FREQUENCY RESPONSE
Bandwidth for 1% Additional
Error (0.09 dB)
VIN = 10 mV 14 14 kHz
VIN = 100 mV 90 90 kHz
VIN = 200 mV 130 130 kHz
±3 dB Bandwidth
VIN = 10 mV 100 100 kHz
VIN = 100 mV 900 900 kHz
VIN = 200 mV 1.5 1.5 MHz
OUTPUT CHARACTERISTICS3
Offset Voltage, VIN = COM
vs. Temperature ±10 ±10 V/°C
vs. Supply ±0.1 ±0.1 mV/V
Voltage Swing
+3 V, −5 V Supply 0.3 0 to 1.0 0.3 0 to 1.0 V
±5 V to ±16.5 V Supply 0.3 0 to 1.0 0.3 0 to 1.0 V
Output Impedance 8 10 12 8 10 12 kΩ
2, 3
3, 5
Min Typ Max Min Typ Max
OUT
1
AD636J AD636K
Unit
2
)
VavgV ×=
IN
±0.5 ± 1.0
±0.5
2
()
OUT
VavgV ×=
IN
±0.2 ± 0.5
±0.2
mV ± % of
ading
re
mV ± % of
ading/°C
re
mV ± % of
ading/V
re
mV ± % of
ading
re
mV
Rev. D | Page 3 of 16
AD636
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AD636J AD636K
Model
Min Typ Max Min Typ Max
dB OUTPUT
Error, VIN = 7 mV to 300 mV rms ±0.3
±0.5
±0.1
±0.2
Scale Factor −3.0 −3.0 mV/dB
Scale Factor Temperature
0.33 0.33 % of reading/°C
Coefficient
−0.033 −0.033 dB/°C
I
for 0 dB = 0.1 V rms
REF
I
Range 1 50 1 50 A
REF
I
TERMINAL
OUT
I
Scale Factor 100 100 A/V rms
OUT
I
Scale Factor Tolerance −20 ±10 +20 −20 ±10 +20 %
OUT
2 4 8 2 4 8
Output Resistance 8 10 12 8 10 12 kΩ
Voltage Compliance
−V
(+V
to
S
− 2 V)
S
−V
(+V
to
S
− 2 V)
S
V
BUFFER AMPLIFIER
Input and Output Voltage Range
−V
(+V
to
S
− 2 V)
S
Input Offset Voltage, RS = 10 kΩ ±0.8
Input Bias Current 100
±2
300
to
−V
S
− 2 V)
(+V
S
±0.5
100
V
±1
300
Input Resistance 108 108 Ω
Output Current
(+5 mA,
−130 A
)
(+5 mA,
−130 A
)
Short-Circuit Current 20 20 mA
Small Signal Bandwidth 1 1 MHz
Slew Rate6 5 5 V/s
POWER SUPPLY
Voltage, Rated Performance +3, −5 +3, −5 V
Dual Supply +2, −2.5 ±16.5 +2, −2.5 ±16.5 V
Single Supply 5 24 5 24 V
Quiescent Current7 0.80
1.00
0.80
1.00
TEMPERATURE RANGE
Rated Performance 0 +70 0 +70 °C
Storage −55 +150 −55 +150 °C
TRANSISTOR COUNT 62 62
1
All minimum and maximum specifications are guaranteed. Specifications shown in boldface are tested on all production units at final electrical test and are used to
calculate outgoing quality levels.
2
Accuracy specified for 0 mV to 200 mV rms, dc or 1 kHz sine wave input. Accuracy is degraded at higher rms signal levels.
3
Measured at Pin 8 of PDIP (I
4
Error vs. crest factor is specified as additional error for a 200 mV rms rectangular pulse trim, pulse width = 200 µs.
5
Input voltages are expressed in V rms.
6
With 10 kΩ pull-down resistor from Pin 6 (BUF OUT) to −VS.
7
With BUF IN tied to COMMON.
), with Pin 9 tied to common.
OUT
Unit
dB
A
mV
nA
mA
Rev. D | Page 4 of 16
AD636
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ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Ratings
Supply Voltage
Dual Supply ±16.5 V
Single Supply 24 V
Internal Power Dissipation 500 mW
Maximum Input Voltage ±12 V
Storage Temperature Range −55°C to +150°C
Operating Temperature Range 0°C to 70°C
Lead Temperature Range (Soldering 60 sec) 300°C
ESD Rating 1000 V
1
10-Lead TO: θJA = 150°C/W.
14-Lead PDIP: θJA = 95°C/W.
1
PEAK
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
Rev. D | Page 5 of 16
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