AD637BQ Просмотр технического описания (PDF) - Analog Devices

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производитель

AD637BQ

High Precision, Wide-Band RMS-to-DC Converter

Analog Devices 

AD637

+VS

OUTPUT

OFFSET 50k⍀

ADJUST

1M⍀

–VS

NOTE: VALUES CHOSEN TO GIVE 0.1%

AVERAGING ERROR @ 1Hz

1␮F

+VS

3.3M⍀ 3.3M⍀

BUFFER

1

AD637

14

1␮F

AD548JN

NC 2

3

BIAS

SECTION

4

5

25k⍀

6

7

ABSOLUTE

VALUE

SQUARER/DIVIDER

25k⍀

FILTER

13

12 NC

SIGNAL

INPUT

11

+VS

–VS

6.8M⍀

1000pF

10

–VS

9

+

100␮F

8

CAV

VIN2

V rms

499k⍀ 1%

CAV1

R

3.3␮F

Figure 15. AD637 as a Low Frequency RMS Converter

FILTERED

V rms OUTPUT

VECTOR SUMMATION

Vector summation can be accomplished through the use of two

AD637s as shown in Figure 16. Here the averaging capacitors

are omitted (nominal 100 pF capacitors are used to insure

stability of the filter amplifier), and the outputs are summed as

shown. The output of the circuit is

VO = VX2 +VY 2

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 ty-

ing all of the denominator inputs (Pin 6) together.

If CAV is added to IC1 in this configuration, the output is

V X 2 +VY 2 . If the averaging capacitor is included on both

IC1 and IC2, the output will be V X 2 +VY 2 .

This circuit has a dynamic range of 10 V to 10 mV and is lim-

ited only by the 0.5 mV offset voltage of the AD637. The useful

bandwidth is 100 kHz.

EXPANDABLE

BUFFER

1

AD637

14

2

3

BIAS

SECTION

4

5

25k⍀

6

7

ABSOLUTE 13

VALUE

12

SQUARER/DIVIDER 11

25k⍀

10

VX IN

+VS

–VS

FILTER

9

100pF

8

BUFFER

1

10k⍀

AD637

14

2

3

BIAS

SECTION

4

5

25k⍀

6

7

ABSOLUTE

VALUE

13 VX IN

12

SQUARER/DIVIDER

11

+VS

25k⍀

10

–VS

9

100pF

FILTER

8

5pF

10k⍀

AD711K

10k⍀

20k⍀

VOUT = VX2 + VV2

Figure 16. AD637 Vector Sum Configuration

REV. E

–9–

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