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芯片手册

AD637

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High Precision, Wideband

RMS-to-DC Converter

AD637

Rev. J

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 www.analog.com

FEATURES

High accuracy

0.02% maximum 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 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

FUNCTIONAL BLOCK DIAGRAM

ABSOLUTE

VALUE

DEN INPUT

RMS OUT

dB OUTPUT

BUFF IN

BUFF

OUT

25kΩ

COMMON

OUTPUT

OFFSET

00788-001

SQUARER/

DIVIDER

BIAS

AD637

Figure 1.

GENERAL DESCRIPTION

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 wide band-

width 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.

As with previous monolithic rms converters from Analog

Devices, Inc., the AD637 has an auxiliary dB output available to

users. 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.

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 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.

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 is also related to the

standard deviation of the signal.

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.

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.

AD637

Rev. J | Page 2 of 20

TABLE OF CONTENTS

Features .............................................................................................. 1

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

Functional Description .................................................................... 7

Standard Connection ................................................................... 8

Chip Select..................................................................................... 8

Optional Trims for High Accuracy............................................ 8

Choosing the Averaging Time Constant....................................9

Frequency Response .................................................................. 11

AC Measurement Accuracy and Crest Factor........................ 12

Connection for dB Output........................................................ 12

dB Calibration............................................................................. 13

Low Frequency Measurements................................................. 14

Vector Summation ..................................................................... 14

Evaluation Board ............................................................................ 16

Outline Dimensions ....................................................................... 19

Ordering Guide .......................................................................... 20

REVISION HISTORY

4/07—Rev. I to Rev. J

Added Evaluation Board Section ................................................. 16

Updated Outline Dimensions....................................................... 20

10/06—Rev. H to Rev. I

Changes to Table 1............................................................................ 3

Changes to Figure 4.......................................................................... 7

Changes to Figure 7.......................................................................... 9

Changes to Figure 16, Figure 18, and Figure 19 ......................... 12

Changes to Figure 20...................................................................... 13

12/05—Rev. G to Rev. H

Updated Format..................................................................Universal

Changes to Figure 1.......................................................................... 1

Changes to Figure 11...................................................................... 10

Updated Outline Dimensions....................................................... 16

Changes to Ordering Guide .......................................................... 17

4/05—Rev. F to Rev. G

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

3/02—Rev. E to Rev. F

Edits to Ordering Guide ...................................................................3

AD637

Rev. J | Page 3 of 20

SPECIFICATIONS

At 25°C and ±15 V dc, unless otherwise noted.

Table 1.

AD637J/AD637A AD637K/AD637B AD637S

Parameter Min Typ Max Min Typ Max Min Typ Max Unit

TRANSFER FUNCTION

OUT

)(V avg × V

OUT

)(V avg × V

OUT

)(V avg ×

CONVERSION ACCURACY

Total Error, Internal Trim

(

Figure 5)

±1 ± 0.5 ±0.5 ± 0.2 ±1 ± 0.5

mV ±% of

reading

MIN

to T

MAX

±3.0 ± 0.6 ±2.0 ± 0.3 ±6 ± 0.7

mV ± % of

reading

vs. Supply

= 300 mV

150

μV/V

vs. Supply

−V

= −300 mV

100

300

100

300

100

300

μV/V

DC Reversal

Error at 2 V

0.25

0.1

0.25

% of

reading

Nonlinearity 2 V Full Scale

0.04

0.02

0.04

% of FSR

Nonlinearity 7 V Full Scale

0.05

% of FSR

Total Error, External Trim ±0.5 ± 0.1 ±0.25 ± 0.05 ±0.5 ± 0.1 mV ± % of

reading

ERROR VS. CREST FACTOR

Crest Factor 1 to 2 Specified accuracy Specified accuracy Specified accuracy

Crest Factor = 3 ±0.1 ±0.1 ±0.1 % of

reading

Crest Factor = 10 ±1.0 ±1.0 ±1.0 % of

reading

AVERAGING TIME CONSTANT 25 25 25 ms/μF C

INPUT CHARACTERISTICS

Signal Range, ±15 V Supply

Continuous RMS Level 0 to 7 0 to 7 0 to 7 V rms

Peak Transient Input ±15 ±15 ±15 V p-p

Signal Range, ±5 V Supply

Continuous RMS Level 0 to 4 0 to 4 0 to 4 V rms

Peak Transient Input ±6 ±6 ±6 V p-p

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

FREQUENCY RESPONSE

Bandwidth for 1%

Additional Error

(0.09 dB)

= 20 mV 11 11 11 kHz

= 200 mV 66 66 66 kHz

= 2 V 200 200 200 kHz

±3 dB Bandwidth

= 20 mV 150 150 150 kHz

= 200 mV 1 1 1 MHz

= 2 V 8 8 8 MHz

AD637

Rev. J | Page 4 of 20

AD637J/AD637A AD637K/AD637B AD637S

Parameter Min Typ Max Min Typ Max Min Typ Max Unit

OUTPUT CHARACTERISTICS

Offset Voltage

±1

±0.5

±1

vs. Temperature ±0.05

±0.089

±0.04

±0.056

±0.04

±0.07

mV/°C

Voltage Swing,

±15 V Supply, 2 kΩ Load

0 to 12.0

13.5

0 to 12.0

13.5

0 to 12.0

13.5 V

Voltage Swing,

±3 V Supply, 2 kΩ Load

0 to 2

2.2

0 to 2

2.2

0 to 2

2.2 V

Output Current

Short-Circuit Current 20 20 20 mA

Resistance

Chip Select High

0.5 0.5 0.5 Ω

Resistance

Chip Select Low

100 100 100 kΩ

dB OUTPUT

Error, V

7 mV to 7 V rms,

0 dB = 1 V rms

±0.5 ±0.3 ±0.5 dB

Scale Factor −3 −3 −3 mV/dB

Scale Factor Temperature

Coefficient

+0.33 +0.33 +0.33 % of

reading/°C

−0.033 −0.033 −0.033 dB/°C

REF

for 0 dB = 1 V rms 5 20

5 20

μA

REF

Range 1 100 1 100 1 100 μA

BUFFER AMPLIFIER

Input Output

Voltage Range

−V

to (+V

− 2.5 V) −V

to (+V

− 2.5 V) −V

to (+V

− 2.5 V) V

Input Offset Voltage ±0.8

±2

±0.5

±1

±0.8

±2

Input Current ±2

±10

±2

±5

±2

±10

Input Resistance 10

Output Current −0.13 +5 −0.13 +5 −0.13 +5 mA

Short-Circuit Current 20 20 20 mA

Small Signal Bandwidth 1 1 1 MHz

Slew Rate

5 5 5 V/μs

DENOMINATOR INPUT

Input Range 0 to 10 0 to 10 0 to 10 V

Input Resistance 20 25 30 20 25 30 20 25 30 kΩ

Offset Voltage ±0.2 ±0.5 ±0.2 ±0.5 ±0.2 ±0.5 mV

CHIP SELECT (CS)

RMS On Level Open or 2.4 V < V

< +V

Open or 2.4 V < V

< +V

Open or 2.4 V < V

< +V

RMS Off Level V

< 0.2 V V

< 0.2 V

OUT

of Chip Select

CS Low 10 10 10 μA

CS High 0 0 0 μA

On Time Constant 10 + ((25 kΩ) × C

) 10 + ((25 kΩ) × C

) μs

Off Time Constant 10 + ((25 kΩ) × C

) 10 + ((25 kΩ) × C

) μs

POWER SUPPLY

Operating Voltage Range

±3.0

±18 ±3.0

±18

Quiescent Current 2.2

2.2

Standby Current 350

450

350

450

350

450

μA

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 minimum and maximum specifications are guaranteed, although only those shown in boldface are tested on all production units.

Accuracy specified 0 V rms to 7 V rms dc with AD637 connected, as shown in Figure 5.

Nonlinearity is defined as the maximum deviation from the straight line connecting the readings at 10 mV and 2 V.

Error vs. crest factor is specified as additional error for 1 V rms.

Input voltages are expressed in volts rms. Percent is in % of reading.

With external 2 kΩ pull-down resistor tied to −V

剩余19页未读，继续阅读

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