5962-8963701CX [ADI]
IC RMS TO DC CONVERTER, 0.15 MHz, CDIP14, CERDIP-14, Analog Special Function Converter;
| 型号： | 5962-8963701CX |
| 厂家： | 
ADI |
| 描述： | IC RMS TO DC CONVERTER, 0.15 MHz, CDIP14, CERDIP-14, Analog Special Function Converter CD 转换器 |
| 文件： | 总20页 (文件大小：515K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
High Precision, Wideband
RMS-to-DC Converter
AD637
FEATURES
High accuracy
FUNCTIONAL BLOCK DIAGRAM
BUFFER
IN
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
BUFFER
OUT
25kΩ
RMS OUT
ABSOLUTE
VALUE
SQUARER/
DIVIDER
V
IN
Computes
True rms
Square
Mean square
25kΩ
DENOMINATOR
IN
C
AV
Absolute value
OUTPUT
OFFSET
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
14-lead SBDIP, 14-lead low cost CERDIP, and 16-lead SOIC_W
BIAS
COM
CS
Figure 1. SBDIP (D-14) and CERDIP (Q-14) Packages
GENERAL DESCRIPTION
The input circuitry of the AD637 is protected from overload
voltages that are in excess of the supply levels. The inputs are
not damaged by input signals if the supply voltages are lost.
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
integrated 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 permits measurements of signals with crest factors of up
to 10 with less than 1% additional error. The circuit’s wide
bandwidth 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.
The AD637 is available in Accuracy Grades J and K for
commercial temperature range (0°C to 70°C) applications;
Accuracy Grades A and B for industrial range (−40°C to +85°C)
applications; 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 packages.
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 ADI, 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.
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 time
period. The value of this capacitor also determines low
frequency 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 facilitates 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 output goes to a
high impedance state. This allows several AD637s to be tied
together to form a wideband true rms multiplexer.
The on-chip buffer amplifier can be 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.
Rev. G
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
Fax: 781.461.3113
www.analog.com
©2005 Analog Devices, Inc. All rights reserved.
AD637
TABLE OF CONTENTS
Specifications..................................................................................... 3
Frequency Response .................................................................. 12
AC Measurement Accuracy and Crest Factor............................ 12
Connection for dB Output........................................................ 13
dB Calibration............................................................................. 15
Low Frequency Measurements................................................. 15
Vector Summation ..................................................................... 15
Outline Dimensions....................................................................... 17
Ordering Guide .......................................................................... 18
Absolute Maximum Ratings............................................................ 6
ESD Caution.................................................................................. 6
Pin Configurations and Function Descriptions ........................... 7
Functional Description.................................................................... 8
Standard Connection................................................................... 9
Chip Select..................................................................................... 9
Optional Trims for High Accuracy............................................ 9
Choosing the Averaging Time Constant................................. 10
REVISION HISTORY
4/05—Rev. F to Rev. G
3/02—Rev. E to Rev. F
Edits to Ordering Guide ...................................................................3
Updated Format..................................................................Universal
Changes to Figure 1.......................................................................... 1
Changes to General Description .................................................... 1
Deleted Product Highlights............................................................. 1
Moved Figure 4 to Page.................................................................... 8
Changes to Figure 5.......................................................................... 9
Changes to Figure 8........................................................................ 10
Changes to Figure 11, Figure 12, Figure 13, and Figure 14....... 11
Changes to Figure 19...................................................................... 14
Changes to Figure 20...................................................................... 14
Changes to Figure 21...................................................................... 16
Updated Outline Dimensions....................................................... 17
Changes to Ordering Guide .......................................................... 18
Rev. G | Page 2 of 20
AD637
SPECIFICATIONS1
At 25°C, and 15 V dc unless otherwise noted.
Table 1.
AD637J/
AD637A
AD637K/
AD637B
AD637S
Typ
Parameter
Min
Typ
Max
Min
Typ
Max
Min
Max
Unit
TRANSFER FUNCTION
VOUT
=
avg ×
VIN 2
)
CONVERSION ACCURACY
Total Error,
Internal Trim2
(Figure 5)
mV ±± of
reading
1
0.5
0.5 0.2
2.0 0.3
1
6
0.5
0.7
TMIN to TMAX
3.0 0.6
mV ± ± of
reading
vs. Supply,
+VIN = +300 mV
30
150
30
100
150
300
0.1
30
150
300
0.25
0.04
0.05
µV/V
vs. Supply,
−VIN = −300 mV
100
300
100
µV/V
DC Reversal
Error at 2 V
0.25
0.04
0.05
± of
reading
Nonlinearity 2 V
Full Scale3
0.02
0.05
± of FSR
Nonlinearity 7 V
Full Scale
± of FSR
Total Error,
External Trim
±0.5 ± 0.1
±0.25 ± 0.05
±0.5 ±
0.1
mV ± ± of
reading
ERROR VS.
CREST FACTOR4
Crest Factor 1 to 2
Crest Factor = 3
Specified Accuracy
±0.1
Specified Accuracy
±0.1
Specified Accuracy
±0.1
± of
reading
Crest Factor = 10
±1.0
25
±1.0
25
±1.0
25
± of
reading
AVERAGING TIME
CONSTANT
ms/µF CAV
INPUT
CHARACTERISTICS
Signal Range,
±15 V Supply
Continuous
RMS Level
0 to 7
0 to 7
0 to 7
V rms
V p-p
Peak Transient
Input
±15
±15
±15
Signal Range,
±5 V Supply
Continuous
RMS Level
0 to 4
0 to 4
0 to 4
V rms
V p-p
Peak Transient
Input
±6
±6
±6
Maximum Continuous
Nondestructive
Input Level (All
Supply Voltages)
±15
±15
±15
V p-p
Input Resistance
6.4
8
9.6
6.4
8
9.6
6.4
8
9.6
kΩ
Input Offset Voltage
±0.5
±0.2
±0.5
mV
Rev. G | Page 3 of 20
AD637
AD637J/
AD637A
AD637K/
AD637B
AD637S
Typ
Parameter
Min
Typ
Max
Min
Typ
Max
Min
Max
Unit
FREQUENCY RESPONSE5
Bandwidth for 1±
Additional Error
(0.09 dB)
VIN = 20 mV
VIN = 200 mV
VIN = 2 V
11
11
11
kHz
kHz
kHz
66
66
66
200
200
200
±3 dB Bandwidth
VIN = 20 mV
VIN = 200 mV
VIN = 2 V
150
1
150
1
150
1
kHz
MHz
MHz
8
8
8
OUTPUT
CHARACTERISTICS
Offset Voltage
1
0.089
0.5
0.056
1
0.07
mV
mV/°C
V
vs. Temperature
±0.05
13.5
±0.04
13.5
±0.04
13.5
Voltage Swing,
±15 V Supply,
2 kΩ Load
0 to
12.0
0 to 12.0
0 to 2
6
0 to
12.0
Voltage Swing,
±3 V Supply,
2 kΩ Load
0 to
2
2.2
2.2
0 to 2
6
2.2
V
Output Current
6
mA
mA
Ω
Short-Circuit Current
20
20
20
Resistance,
0.5
0.5
0.5
Chip Select High
Resistance,
100
100
100
kΩ
Chip Select Low
dB OUTPUT
Error, VIN 7 mV to
7 V rms, 0 dB =
1 V rms
±0.5
−3
±0.3
−3
±0.5
−3
dB
Scale Factor
mV/dB
Scale Factor
Temperature
Coefficient
± of
Reading/°C
+0.33
−0.033
20
+0.33
−0.033
20
+0.33
−0.033
20
dB/°C
µA
IREF for 0 dB = 1 V rms
IREF Range
5
1
80
100
5
1
80
100
5
1
80
100
µA
BUFFER AMPLIFIER
Input Output
−VS to (+VS − 2.5 V)
−VS to (+VS − 2.5 V)
−VS to (+VS − 2.5 V)
V
Voltage Range
Input Offset Voltage
Input Current
±0.8
2
±0.5
1
5
±0.8
±2
mV
nA
±2
108
10
±2
108
±2
108
±10
Input Resistance
Output Current
Ω
−0.13
20
5
−0.13
20
5
−0.13
20
5
mA
mA
MHz
Short Circuit Current
Small Signal
Bandwidth
Slew Rate6
1
1
1
5
5
5
V/µs
DENOMINATOR INPUT
Input Range
0 to 10
0 to 10
0 to 10
V
Input Resistance
Offset Voltage
20
25
30
20
25
30
20
25
30
kΩ
mV
±0.2
±0.5
±0.2
±0.5
±0.2
±0.5
Rev. G | Page 4 of 20
AD637
AD637J/
AD637A
AD637K/
AD637B
AD637S
Typ
Parameter
Min
Typ
Max
Min
Typ
Max
Min
Max
Unit
CHIP SELECT (CS)
RMS ON Level
RMS OFF Level
Open or 2.4 V < VC < +VS
Open or 2.4 V < VC < +VS
VC < 0.2 V
Open or 2.4 V < VC < +VS
VC <
VC < 0.2 V
0.2 V
IOUT of Chip Select
CS Low
10
0
10
0
10
0
µA
µA
µs
CS High
On Time Constant
Off Time Constant
POWER SUPPLY
10 + ((25 kΩ) × CAV
10 + ((25 kΩ) × CAV
)
)
10 + ((25 kΩ) × CAV
10 + ((25 kΩ) × CAV
)
)
10 + ((25 kΩ) × CAV
10 + ((25 kΩ) × CAV
)
)
µs
Operating Voltage
Range
3.0
18
3.0
18
3.0
18
V
Quiescent Current
Standby Current
2.2
3
2.2
3
2.2
3
mA
µA
350
450
350
450
350
450
1 Specifications shown in bold are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min and
max specifications are guaranteed, although only those shown in boldface are tested on all production units.
2 Accuracy specified 0 V rms to 7 V rms dc with AD637 connected as shown in Figure 5.
3 Nonlinearity is defined as the maximum deviation from the straight line connecting the readings at 10 mV and 2 V.
4 Error vs. crest factor is specified as additional error for 1 V rms.
5 Input voltages are expressed in volts rms. Percent is in ± of reading.
6 With external 2 kΩ pull-down resistor tied to −VS.
Rev. G | Page 5 of 20
AD637
ABSOLUTE MAXIMUM RATINGS
Table 2.
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.
Parameter
Rating
ESD Rating
Supply Voltage
500 V
±18 V dc
108 mW
Indefinite
−65°C to +150°C
300°C
Internal Quiescent Power Dissipation
Output Short-Circuit Duration
Storage Temperature Range
Lead Temperature Range (Soldering 10 secs)
Rated Operating Temperature Range
AD637J, AD637K
0°C to 70°C
AD637A, AD637B
AD637S, 5962-8963701CA
−40°C to +85°C
−55°C to +125°C
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degrada-
tion or loss of functionality.
Rev. G | Page 6 of 20
AD637
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
14
13
12
11
10
9
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
BUFF OUT
BUFF IN
NC
BUFF IN
NC
BUFF OUT
V
V
IN
IN
NC
COMMON
OUTPUT OFFSET
CS
NC
COMMON
OUTPUT OFFSET
CS
AD637
AD637
+V
S
+V
S
TOP VIEW
TOP VIEW
(Not to Scale)
–V
S
–V
S
(Not to Scale)
DEN INPUT
dB OUTPUT
RMS OUT
RMS OUT
DEN INPUT
dB OUTPUT
NC
8
C
C
AV
AV
NC
NC = NO CONNECT
NC = NO CONNECT
Figure 2. 14-Lead SBDIP/CERDIP Pin Configuration
Figure 3. 16-Lead SOIC_W Pin Configuration
Table 3. 14-Lead SBDIP/CERDIP Pin Function Descriptions
Table 4. 16-Lead SOIC_W Pin Function Descriptions
Pin No. Mnemonic
Description
Pin No.
Mnemonic
Description
1
2, 12
3
BUFF IN
NC
COMMON
Buffer Input
No Connection
Analog Common
1
BUFF IN
Buffer Input
No Connection
Analog Common
2, 8, 9, 14 NC
3
COMMON
4
OUTPUT OFFSET Output Offset
4
OUTPUT OFFSET Output Offset
5
CS
Chip Select
5
CS
Chip Select
6
7
8
9
10
11
13
14
DEN INPUT
dB OUTPUT
CAV
RMS OUT
−VS
+VS
VIN
BUFF OUT
Denominator Input
dB Output
Averaging Capacitor Connection
RMS Output
Negative Supply Rail
Positive Supply Rail
Signal Input
6
7
DEN INPUT
dB OUTPUT
CAV
RMS OUT
−VS
+VS
VIN
BUFF OUT
Denominator Input
dB Output
Averaging Capacitor Connection
RMS Output
Negative Supply Rail
Positive Supply Rail
Signal Input
10
11
12
13
15
16
Buffer Output
Buffer Output
Rev. G | Page 7 of 20
AD637
FUNCTIONAL DESCRIPTION
FILTER/AMPLIFIER
8
11
9
CAV
14
BUFF OUT
ONE QUADRANT
SQUARER/DIVIDER
24kΩ
+V
S
1
BUFF IN
BUFFER
AMPLIFIER
A5
RMS
OUT
A4
I
4
dB
7
3
I
OUT
1
24kΩ
COM
Q4
Q1
ABSOLUTE VALUE VOLTAGE –
CURRENT CONVERTER
CS
5
6
4
Q5
BIAS
DEN
INPUT
I
24kΩ
Q2
Q3
A3
3
6kΩ
6kΩ
OUTPUT
OFFSET
A2
12kΩ
125Ω
AD637
V
13
IN
A1
10 –V
S
Figure 4. Simplified Schematic
The AD637 embodies an implicit solution of the rms equation
that overcomes the inherent limitations of straightforward rms
computation. The actual computation performed by the AD637
follows the equation
If the averaging capacitor is omitted, the AD637 computes the
absolute value of the input signal. A nominal 5 pF capacitor
should be used to ensure stability. The circuit operates
identically to that of the rms configuration except that I3 is
now equal to I4, giving
V
⎡
⎢
⎤
⎥
2
ΙΝ
V rms = Avg
I12
V rms
⎢
⎣
⎥
⎦
I4 =
I4
Figure 4 is a simplified schematic of the AD637, subdivided into
four major sections: absolute value circuit (active rectifier),
squarer/divider, filter circuit, and buffer amplifier. The input
voltage VIN, which can be ac or dc, is converted to a unipolar
current I1 by the active rectifier A1, A2. I1 drives one input of
the squarer/divider, which has the transfer function
I4 = I1
The denominator current can also be supplied externally
by providing a reference voltage, VREF, to Pin 6. The circuit
operates identically to the rms case except that I3 is now
proportional to VREF. Therefore,
2
I1
I12
I3
I4 =
I4 = Avg
I3
The output current of the squarer/divider I4 drives A4, which
forms a low-pass filter with the external averaging capacitor.
If the RC time constant of the filter is much greater than the
longest period of the input signal, A4’s output is proportional to
the average of I4. The output of this filter amplifier is used by A3
to provide the denominator current I3, which equals Avg I4 and
is returned to the squarer/divider to complete the implicit rms
computation
and
2
VIN
VO =
VDEN
This is the mean square of the input signal.
2
⎡
⎢
⎣
⎤
⎥
⎦
I1
I4
I = Avg
= I rms
1
4
and
VOUT = VIN rms
Rev. G | Page 8 of 20
AD637
20
15
10
5
STANDARD CONNECTION
The AD637 is simple to connect for a majority of rms
measurements. In the standard rms connection shown in
Figure 5, only a single external capacitor is required to set the
averaging time constant. In this configuration, the AD637
computes the true rms of any input signal. An averaging error,
the magnitude of which is dependent on the value of the
averaging capacitor, is present at low frequencies. For example,
if the filter capacitor, CAV, is 4 µF, the error is 0.1% at 10 Hz and
increases to 1% at 3 Hz. To measure ac signals, the AD637 can
be ac-coupled through the addition of a nonpolar capacitor in
series with the input, as shown in Figure 5.
0
0
± 3
± 5
± 10
± 15
± 18
SUPPLY VOLTAGE – DUAL SUPPLY (V)
AD637
1
BUF IN
BUFFER
OUT
14
NC
Figure 6. AD637 Maximum VOUT vs. Supply Voltage
2
3
NC
V
IN
V
IN
13
ABSOLUTE
VALUE
CHIP SELECT
COM
NC 12
11
+V
S
The AD637 includes a chip select feature that allows the user to
decrease the quiescent current of the device from 2.2 mA to
350 µA. This is done by driving the CS, Pin 5, to below 0.2 V dc.
Under these conditions, the output goes into a high impedance
state. In addition to lowering power consumption, this feature
permits bussing the outputs of a number of AD637s to form a
wide bandwidth rms multiplexer. If the chip select is not being
used, Pin 5 should be tied high.
(OPTIONAL)
SQUARER/
DIVIDER
OUT
OFF
4
5
6
7
+V
BIAS
+V
S
S
4.7kΩ
CS
10
9
–V
–V
S
S
25kΩ
DEN
IN
2
= V
IN
V
OUT
25kΩ
C
+
8
AV
C
DB OUT
AV
OPTIONAL TRIMS FOR HIGH ACCURACY
The AD637 includes provisions for trimming out output offset
and scale factor errors resulting in significant reduction in the
maximum total error, as shown in Figure 7. The residual error is
due to a nontrimmable input offset in the absolute value circuit
and the irreducible nonlinearity of the device.
Figure 5. Standard RMS Connection
The performance of the AD637 is tolerant of minor variations
in the power supply voltages; however, if the supplies used
exhibit a considerable amount of high frequency ripple, it is
advisable to bypass both supplies to ground through a 0.1 µF
ceramic disc capacitor placed as close to the device as possible.
Referring to Figure 8, the trimming process follows:
The output signal range of the AD637 is a function of the
supply voltages, as shown in Figure 6. The output signal can be
used buffered or nonbuffered, depending on the characteristics
of the load. If no buffer is needed, tie the buffer input (Pin 1) to
common. The output of the AD637 is capable of driving 5mA
into a 2 kΩ load without degrading the accuracy of the device.
• Offset trim: Ground the input signal, VIN, and adjust R1
to give 0 V output from Pin 9. Alternatively, R1 can be
adjusted to give the correct output with the lowest expected
value of VIN.
• Scale factor trim: Resistor R4 is inserted in series with
the input to lower the range of the scale factor. Connect
the desired full-scale input to VIN, using either a dc or a
calibrated ac signal, and trim R3 to give the correct output
at Pin 9, that is, 1 V dc should give l.000 V dc output. Of
course, a 2 V p-p sine wave should give 0.707 V dc output.
Remaining errors are due to the nonlinearity.
Rev. G | Page 9 of 20
AD637
5.0
E
O
IDEAL
E
AD637K MAX
O
DC ERROR = AVERAGE OF OUTPUT – IDEAL
2.5
0
INTERNAL TRIM
AD637K
AVERAGE ERROR
DOUBLE-FREQUENCY
RIPPLE
EXTERNAL TRIM
TIME
Figure 9. Typical Output Waveform for a Sinusoidal Input
2.5
This ripple can add a significant amount of uncertainty to the
accuracy of the measurement being made. The uncertainty can
be significantly reduced through the use of a post filtering
network or by increasing the value of the averaging capacitor.
AD637K: 0.5mV ± 0.2%
0.25mV ± 0.05%
EXTERNAL
5.0
0
0.5
1.0
INPUT LEVEL (V)
1.5
2.0
The dc error appears as a frequency dependent offset at the
output of the AD637 and follows the equation
Figure 7. Maximum Total Error vs.
Input Level AD637K Internal and External Trims
1
in% of reading
0.16 + 6.4 τ2 f 2
AD637
1
BUF IN
BUFFER
OUT
14
NC
R4
Since the averaging time constant, set by CAV, directly sets the
time that the rms converter holds the input signal during
computation, the magnitude of the dc error is determined only
by CAV and is not affected by post filtering.
2
3
NC
V
147Ω IN
V
IN 13
ABSOLUTE
VALUE
OUTPUT
OFFSET
TRIM
COM
NC 12
11
+V
S
R2
1MΩ
SQUARER/
DIVIDER
OUT
OFF
4
5
6
7
R1
50kΩ
+V
BIAS
+V
S
S
100
4.7kΩ
–V
CS
10
S
+V
–V
–V
S
S
S
25kΩ
DEN
IN
2
= V
IN
V
OUT
25kΩ
9
C
+
8
AV
C
DB OUT
AV
10
SCALE FACTOR TRIM
PEAK RIPPLE
R3
1kΩ
1.0
Figure 8. Optional External Gain and Offset Trims
DC ERROR
CHOOSING THE AVERAGING TIME CONSTANT
The AD637 computes the true rms value of both dc and ac
0.1
input signals. At dc, the output tracks the absolute value of the
input exactly; with ac signals, the AD637’s output approaches
the true rms value of the input. The deviation from the ideal
rms value is due to an averaging error. The averaging error is
comprised of an ac and dc component. Both components are
functions of input signal frequency f and the averaging time
constant τ (τ: 25 ms/µF of averaging capacitance). Figure 9
shows that the averaging error is defined as the peak value of
the ac component, ripple, and the value of the dc error.
10
100
1k
10k
SINEWAVE INPUT FREQUENCY (Hz)
Figure 10. Comparison of Percent DC Error to the
Percent Peak Ripple over Frequency Using the
AD637 in the Standard RMS Connection with a 1 × µF CAV
The ac ripple component of averaging error is greatly reduced
by increasing the value of the averaging capacitor. There are two
major disadvantages to this: the value of the averaging capacitor
becomes extremely large and the settling time of the AD637
increases in direct proportion to the value of the averaging
capacitor (Ts = 115 ms/µF of averaging capacitance). A
preferable method of reducing the ripple is through the use of
the post filter network, as shown in Figure 11. This network can
be used in either a one-pole or two-pole configuration. For
most applications, the single pole filter gives the best overall
compromise between ripple and settling time.
The peak value of the ac ripple component of the averaging
error is defined approximately by the relationship
50
6.3 τf
in% of reading where
(
τ >1 f
)
Rev. G | Page 10 of 20
AD637
100
10
100
AD637
1
BUF IN
BUFFER
OUT
14 RMS OUT
13
0
.
0
1
%
E
2
3
NC
V
R
IN
ABSOLUTE
0
R
V
.
O
IN
1
10
%
VALUE
R
E
+
R
COM
R
C3
1
%
NC 12
11
O
R
E
SQUARER/
DIVIDER
R
OUT
OFF
R
O
1
4
5
6
7
0
R
+V
%
BIAS
+V
–V
S
S
1.0
1.0
0.1
0.01
E
R
R
O
+V
S
4.7kΩ
CS
10
R
–V
S
S
25kΩ
DEN
IN
25kΩ
9
0.1
C
+
8
AV
C
DB OUT
AV
*%dc ERROR + %RIPPLE (PEAK)
0.01
1
10
100
1k
10k
100k
INPUT FREQUENCY (Hz)
24kΩ
FOR A1 POLE
FILTER SHORT Rx
AND REMOVE C3
24kΩ
+
Figure 12. Values for CAV, and 1% Settling Time for Stated % of Reading
Averaging Error* Accuracy Includes 2% Component Tolerance
(see * in Figure)
C2
100
100
10
1
Figure 11. Two-Pole Sallen-Key Filter
Figure 12 shows values of CAV and the corresponding averaging
error as a function of sine wave frequency for the standard rms
connection. The 1% settling time is shown on the right side of
Figure 12.
10
0
.
0
1
Figure 13 shows the relationship between the averaging error,
signal frequency settling time, and averaging capacitor value.
Figure 13 is drawn for filter capacitor values of 3.3× the
averaging capacitor value. This ratio sets the magnitude of the
ac and dc errors equal at 50 Hz. As an example, by using a 1 µF
averaging capacitor and a 3.3 µF filter capacitor, the ripple for a
60 Hz input signal is reduced from 5.3% of the reading using
the averaging capacitor alone to 0.15% using the single-pole
filter. This gives a factor of 30 reduction in ripple and yet the
settling time only increases by a factor of 3. The values of CAV
and C2, the filter capacitors, can be calculated for the desired
value of averaging error and settling time by using Figure 13.
%
0
1
.
1
E
%
R
R
1
E
%
O
R
R
R
E
5
O
R
%
R
R
E
O
R
R
R
O
0.1
0.01
0.1
R
*%dc ERROR + %RIPPLE (PEAK)
ACCURACY ±20% DUE TO
COMPONENT TOLERANCE
0.01
100k
1
10
100
1k
10k
INPUT FREQUENCY (Hz)
Figure 13. Values of CAV, C2, and 1% Settling Time for Stated % of Reading
Averaging Error* for 1-Pole Post Filter (see * in Figure)
100
10
1
100
The symmetry of the input signal also has an effect on the
magnitude of the averaging error. Table 5 gives the practical
component values for various types of 60 Hz input signals.
These capacitor values can be directly scaled for frequencies
other than 60 Hz; that is, for 30 Hz these values are doubled, for
120 Hz they are halved.
10
0
.
0
1
%
1
0
.
1
E
R
%
R
1
R
E
%
O
R
R
E
R
5
R
O
%
R
E
For applications that are extremely sensitive to ripple, the two-
pole configuration is suggested. This configuration minimizes
capacitor values and the settling time while maximizing
performance.
O
R
R
R
O
0.1
0.01
0.1
R
*%dc ERROR + %RIPPLE (PEAK)
ACCURACY ±20% DUE TO
COMPONENT TOLERANCE
0.01
100k
1
10
100
1k
10k
Figure 14 can be used to determine the required value of CAV,
C2, and C3 for the desired level of ripple and settling time.
INPUT FREQUENCY (Hz)
Figure 14. Values of CAV, C2, and C3 and 1% Settling Time for Stated % of
Reading Averaging Error* 2-Pole Sallen-Key Filter (see * in Figure)
Rev. G | Page 11 of 20
AD637
Table 5. Practical Values of CAV and C2 for Various Input Waveforms
Recommended CAV and C2 Values
for 1% Averaging Error @ 60 Hz with T = 16.6 ms
Absolute Value
Input Waveform
and Period
Circuit Waveform
and Period
Minimum
R × CAV Time Constant
1% Settling
Time
Recommended
Standard Value CAV
Recommended
Standard Value C2
1/2T
T
1/2T
0.47 µF
0.82 µF
1.5 µF
2.7 µF
181 ms
A
0V
Symmetrical Sine Wave
T
T
T
325 ms
B
0V
Sine Wave with dc Offset
T
T
10 (T − T2)
6.8 µF
5.6 µF
22 µF
18 µF
2.67 sec
2.17 sec
C
D
T
2
T
2
0V
Pulse Train Waveform
T
T
10 (T − 2T2)
T
2
T
2
0V
FREQUENCY RESPONSE
The frequency response of the AD637 at various signal levels is
shown in Figure 15. The dashed lines show the upper frequency
limits for 1%, 10%, and 3 dB of additional error. For example,
note that for 1% additional error with a 2 V rms input, the
highest frequency allowable is 200 kHz. A 200 mV signal can be
measured with 1% error at signal frequencies up to 100 kHz.
10
7V RMS INPUT
2V RMS INPUT
1V RMS INPUT
1
0.1
1%
10%
±3dB
100mV RMS INPUT
100mV RMS INPUT
To take full advantage of the wide bandwidth of the AD637,
care must be taken in the selection of the input buffer amplifier.
To ensure that the input signal is accurately presented to the
converter, the input buffer must have a −3 dB bandwidth that is
wider than that of the AD637. Note the importance of slew rate
in this application. For example, the minimum slew rate
required for a 1 V rms, 5 MHz, sine wave input signal is
44 V/µs. The user is cautioned that this is the minimum rising
or falling slew rate and that care must be exercised in the
selection of the buffer amplifier, since some amplifiers exhibit a
two-to-one difference between rising and falling slew rates. The
AD845 is recommended as a precision input buffer.
0.01
1k
10k
100k
1M
10M
INPUT FREQUENCY (Hz)
Figure 15. Frequency Response
AC MEASUREMENT ACCURACY AND CREST FACTOR
Crest factor is often overlooked in determining the accuracy of
an ac measurement. Crest factor is defined as the ratio of the peak
signal amplitude to the rms value of the signal (CF = Vp/V rms).
Most common waveforms, such as sine and triangle waves, have
relatively low crest factors (≤2). Waveforms that resemble low
duty cycle pulse trains, such as those occurring in switching
power supplies and SCR circuits, have high crest factors. For
example, a rectangular pulse train with a 1% duty cycle has a
crest factor of 10 (CF = 1 η ).
Rev. G | Page 12 of 20
AD637
100
T
µs
T
η
= DUTY CYCLE =
2.0
1.8
1.6
Vp
η
e0
CF = 1/
0
eIN(RMS) = 1 V RMS
100µF
10
1.4
1.2
C
= 22µF
AV
CF = 10
CF = 7
1.0
0.8
1
CF = 10
0.6
0.4
0.2
0
CF = 3
0.1
0.5
1.0
(V rms)
1.5
2.0
0
V
IN
CF = 3
Figure 18. Error vs. RMS Input Level for Three Common Crest Factors
0.01
1
10
PULSE WIDTH (
100
1000
CONNECTION FOR DB OUTPUT
µ
s)
Another feature of the AD637 is the logarithmic, or decibel,
output. The internal circuit that computes dB works well over a
60 dB range. Figure 19 shows the dB measurement connection.
The user selects the 0 dB level by setting R1 for the proper 0 dB
reference current, which is set to exactly cancel the log output
current from the squarer/divider circuit at the desired 0 dB
point. The external op amp is used to provide a more
convenient scale and to allow compensation of the +0.33%/°C
temperature drift of the dB circuit. The special TC resistor R3 is
available from Precision Resistor Inc., Largo, Fla (Model PT146).
Figure 16. AD637 Error vs. Pulse Width Rectangular Pulse
Figure 17 is a curve of additional reading error for the AD637
for a 1 V rms input signal with crest factors from 1 to 11. A
rectangular pulse train (pulse width 100 µs) was used for this
test because it is the worst-case waveform for rms measurement
(all the energy is contained in the peaks). The duty cycle and
peak amplitude were varied to produce crest factors from l to 10
while maintaining a constant 1 V rms input amplitude.
1.5
1.0
0.5
0
–0.5
POSITIVE INPUT PULSE
C
= 22µF
AV
–1.0
–1.5
3
4
5
6
7
1
2
8
9
10
11
CREST FACTOR
Figure 17. Additional Error vs. Crest Factor
Rev. G | Page 13 of 20
AD637
R2
5k
dB SCALE
FACTOR
ADJUST
33.2kΩ
SIGNAL
INPUT
Ω
+V
S
BUFFER
R3
60.4
BUFFER
OUT 14
AD637
Ω
BUF IN
1
2
3
4
5
6
7
*1kΩ
AD707JN
V
IN
13
ABSOLUTE
VALUE
NC
COMPENSATED
dB OUTPUT
+ 100mV/dB
COM
12
11
NC
–V
S
BIAS
SECTION
OUT
OFF
SQUARER/DIVIDER
+V
+V
–V
S
S
S
25kΩ
4.7kΩ
CS
10
9
+V
S
–V
S
DEN
IN
V
25k
Ω
OUT
+
1µF
dB
8
FILTER
C
AV
10kΩ
+V
S
*1k
Ω + 3500ppm
R1
500k
TC RESISTOR TEL LAB Q81
PRECISION RESISTOR PT146
OR EQUIVALENT
Ω
+2.5 VOLTS
AD508J
NC = NO CONNECT
0dB ADJUST
Figure 19. dB Connection
+V
1µF
S
NOTE: VALUES CHOSEN TO GIVE 0.1%
AVERAGING ERROR @ 1Hz
Ω
3.3MΩ 3.3M
1µF
AD548JN
BUFFER
BUFFER
OUT
AD637
FILTERED
V RMS OUTPUT
14
BUF IN
1
2
3
V
IN 13
–V
S
SIGNAL
INPUT
ABSOLUTE
VALUE
NC
6.8MΩ
COM
12
11
10
NC
+V
S
BIAS
SECTION
OUT
OFF
1000pF
1MΩ
OUTPUT
OFFSET
ADJUST
SQUARER/DIVIDER
4
5
+V
+V
S
50kΩ
S
25kΩ
+V
CS
S
–V
S
–V
S
–V
S
4.7kΩ
V
2
25kΩ
OUT
9
+
V
IN
DEN
IN
V rms
6
100µF
C
8
AV
FILTER
7
dB
1%
499kΩ
R
C
3.3µF
AV1
NC = NO CONNECT
Figure 20. AD637 as a Low Frequency RMS Converter
Rev. G | Page 14 of 20
AD637
If the frequency of interest is below 1 Hz, or if the value of
dB CALIBRATION
the averaging capacitor is still too large, the 20:1 ratio can be
increased. This is accomplished by increasing the value of R. If
this is done, it is suggested that a low input current, low offset
voltage amplifier, such as the AD548, be used instead of the
internal buffer amplifier. This is necessary to minimize the
offset error introduced by the combination of amplifier input
currents and the larger resistance.
Refer to Figure 19:
• Set VIN = 1.00 V dc or 1.00 V rms
• Adjust R1 for 0 dB out = 0.00 V
• Set VIN = 0.1 V dc or 0.10 V rms
• Adjust R2 for dB out = −2.00 V
Any other dB reference can be used by setting VIN and R1
accordingly.
VECTOR SUMMATION
Vector summation can be accomplished through the use of two
AD637s, as shown in Figure 21. Here the averaging capacitors
are omitted (nominal 100 pF capacitors are used to ensure
stability of the filter amplifier), and the outputs are summed as
shown. The output of the circuit is
LOW FREQUENCY MEASUREMENTS
If the frequencies of the signals to be measured are below
10 Hz, the value of the averaging capacitor required to deliver
even 1% averaging error in the standard rms connection
becomes extremely large. Figure 20 shows an alternative
method of obtaining low frequency rms measurements. The
averaging time constant is determined by the product of R and
CAV1, in this circuit 0.5 s/µF of CAV. This circuit permits a 20:1
reduction in the value of the averaging capacitor, permitting the
use of high quality tantalum capacitors. It is suggested that the
two-pole, Sallen-Key filter shown in Figure 20 be used to obtain
a low ripple level and minimize the value of the averaging
capacitor.
2
2
VO = VX +VY
This concept can be expanded to include additional terms by
feeding the signal from Pin 9 of each additional AD637 through
a 10 kΩ resistor to the summing junction of the AD711 and
tying all of the denominator inputs (Pin 6) together.
If CAV is added to IC1 in this configuration, the output is
2
2
VX + VY
If the averaging capacitor is included on both IC1 and IC2, the
output is
2
VX2 +VY
This circuit has a dynamic range of 10 V to 10 mV and is
limited only by the 0.5 mV offset voltage of the AD637. The
useful bandwidth is 100 kHz.
Rev. G | Page 15 of 20
AD637
EXPANDABLE
BUFFER
AD637
BUFFER
OUT
IC1
BUF IN
14
13
1
V IN
X
ABSOLUTE
VALUE
2
3
NC
12
11
COM
NC
BIAS
OUT
OFF
SECTION
SQUARER/DIVIDER
25k
4
5
6
+V
+V
S
S
S
Ω
+V
10
S
CS
–V
–V
S
4.7kΩ
V
25k
Ω
OUT
9
DEN
IN
100pF
8
5pF
C
FILTER
AV
7
dB
10k
Ω
10k
Ω
BUFFER
BUFFER
OUT
AD637
IC2
BUF IN
1
14
AD711K
V IN
Y
2
3
4
5
6
NC
ABSOLUTE
VALUE
13
COM
NC 12
10k
20k
Ω
Ω
BIAS
SECTION
OUT
OFF
11
10
SQUARER/DIVIDER
25k
+V
–V
+V
S
S
S
Ω
+V
S
CS
–V
S
4.7kΩ
DEN
IN
V
25k
Ω
OUT
9
8
100pF
dB
FILTER
7
2
2
V
=
V
+ V
X Y
OUT
Figure 21. Vector Sum Configuration
Rev. G | Page 16 of 20
AD637
OUTLINE DIMENSIONS
0.005 (0.13) MIN
0.080 (2.03) MAX
8
14
0.310 (7.87)
1
0.220 (5.59)
7
PIN 1
0.100 (2.54)
BSC
0.320 (8.13)
0.290 (7.37)
0.765 (19.43) MAX
0.060 (1.52)
0.015 (0.38)
0.200 (5.08)
MAX
0.150
(3.81)
MIN
0.200 (5.08)
0.125 (3.18)
0.015 (0.38)
0.008 (0.20)
SEATING
PLANE
0.070 (1.78)
0.030 (0.76)
0.023 (0.58)
0.014 (0.36)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 22. 14-Lead Side-Brazed Ceramic Dual In-Line Package [SBDIP]
(D-14)
Dimensions shown in inches and (millimeters)
0.098 (2.49) MAX
8
0.005 (0.13) MIN
14
0.310 (7.87)
0.220 (5.59)
1
7
PIN 1
0.320 (8.13)
0.290 (7.37)
0.100 (2.54) BSC
0.785 (19.94) MAX
0.060 (1.52)
0.015 (0.38)
0.200 (5.08)
MAX
0.150
(3.81)
MIN
0.200 (5.08)
0.125 (3.18)
0.015 (0.38)
0.008 (0.20)
SEATING
PLANE
0.023 (0.58)
0.014 (0.36)
15°
0°
0.070 (1.78)
0.030 (0.76)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 23. 14-Lead Ceramic Dual In-Line Package [CERDIP]
(Q-14)
Dimensions shown in inches and (millimeters)
Rev. G | Page 17 of 20
AD637
10.50 (0.4134)
10.10 (0.3976)
16
1
9
8
7.60 (0.2992)
7.40 (0.2913)
10.65 (0.4193)
10.00 (0.3937)
1.27 (0.0500)
BSC
0.75 (0.0295)
0.25 (0.0098)
2.65 (0.1043)
2.35 (0.0925)
× 45°
0.30 (0.0118)
0.10 (0.0039)
8°
0°
0.51 (0.0201)
0.31 (0.0122)
SEATING
PLANE
COPLANARITY
0.10
1.27 (0.0500)
0.40 (0.0157)
0.33 (0.0130)
0.20 (0.0079)
COMPLIANT TO JEDEC STANDARDS MS-013-AA
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
Figure 24. 16-Lead Standard Small Outline Package [SOIC_W]
Wide Body
(RW-16)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model
Temperature Range
−55°C to +125°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
0°C to 70°C
Package Description
14-Lead CERDIP
14-Lead CERDIP
16-Lead SOIC_W
14-Lead CERDIP
16-Lead SOIC_W
14-Lead SBDIP
Package Option
Q-14
Q-14
RW-16
Q-14
RW-16
D-14
5962-8963701CA1
AD637AQ
AD637AR
AD637BQ
AD637BR
AD637JD
AD637JQ
AD637JR
0°C to 70°C
0°C to 70°C
0°C to 70°C
0°C to 70°C
0°C to 70°C
0°C to 70°C
0°C to 70°C
0°C to 70°C
14-Lead CERDIP
16-Lead SOIC_W
16-Lead SOIC_W
16-Lead SOIC_W
16-Lead SOIC_W
16-Lead SOIC_W
16-Lead SOIC_W
14-Lead SBDIP
Q-14
RW-16
RW-16
RW-16
RW-16
RW-16
RW-16
D-14
AD637JR-REEL
AD637JR-REEL7
AD637JRZ2
AD637JRZ-R72
AD637JRZ-RL2
AD637KD
AD637KQ
AD637KR
AD637SD
AD637SD/883B
AD637SQ/883B
0°C to 70°C
0°C to 70°C
−55°C to +125°C
−55°C to +125°C
−55°C to +125°C
14-Lead CERDIP
16-Lead SOIC_W
14-Lead SBDIP
14-Lead SBDIP
14-Lead CERDIP
Q-14
RW-16
D-14
D-14
Q-14
1 A standard microcircuit drawing is available.
2 Z = Pb-free part.
Rev. G | Page 18 of 20
AD637
NOTES
Rev. G | Page 19 of 20
AD637
NOTES
©2005 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C00788–0–4/05(G)
Rev. G | Page 20 of 20
相关型号：
5962-8964101CA
Operational Amplifier, 1 Func, 5500uV Offset-Max, BIPolar, CDIP14, HERMETIC SEALED, CERDIP-14
ROCHESTER
©2020 ICPDF网 联系我们和版权申明