AD637B AD [Analog Devices], AD637B Datasheet - Page 9

• Manufacturer Part Number: AD637B
• Description: High Precision, Wide-Band RMS-to-DC Converter
• Manufacturer: AD [Analog Devices]

REV. E
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
This concept can be expanded to include additional terms by
feeding the signal from Pin 9 of each additional AD637 through
a 10 k resistor to the summing junction of the AD711, and ty-
ing all of the denominator inputs (Pin 6) together.
If C
IC1 and IC2, the output will be
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.
V
AV
X
2
is added to IC1 in this configuration, the output is
V
Y
2
OUTPUT
OFFSET
ADJUST
. If the averaging capacitor is included on both
50k
V
+V
–V
O
S
S
1M
V
X
2
NOTE: VALUES CHOSEN TO GIVE 0.1%
NC
V
V
Figure 15. AD637 as a Low Frequency RMS Converter
X
4
1
2
3
5
6
7
Y
2
AVERAGING ERROR @ 1Hz
2
25k
V
SECTION
Y
BIAS
2
BUFFER
.
C
3.3 F
AV1
SQUARER/DIVIDER
499k
ABSOLUTE
R
VALUE
AD637
FILTER
1%
25k
–9–
14
13
12
11
10
9
8
+
NC
C
AV
1
2
3
4
5
6
7
1
2
3
4
5
6
7
3.3M
100 F
+V
–V
Figure 16. AD637 Vector Sum Configuration
25k
25k
S
S
SECTION
SECTION
SIGNAL
INPUT
BIAS
BIAS
3.3M
BUFFER
BUFFER
1 F
EXPANDABLE
V
V rms
1 F
IN
SQUARER/DIVIDER
SQUARER/DIVIDER
2
6.8M
AD548JN
ABSOLUTE
ABSOLUTE
1000pF
VALUE
VALUE
+V
–V
AD637
FILTER
AD637
FILTER
S
S
25k
25k
10
14
10
14
13
12
11
12
11
13
8
9
8
9
V rms OUTPUT
100pF
10k
FILTERED
V
V
100pF
X
+V
+V
X
–V
–V
IN
IN
S
S
S
S
V
AD637
OUT
5pF
AD711K
10k
=
10k
20k
V
X
2
+ V
V
2