AD637JQ Analog Devices Inc, AD637JQ Datasheet - Page 7

• Manufacturer Part Number: AD637JQ
• Description: IC RMS/DC CONV PRECISION 14-CDIP
• Manufacturer: Analog Devices Inc

Specifications of AD637JQ

• Rohs Status: RoHS non-compliant
• Current - Supply: 2.2mA
• Voltage - Supply: ±3.0V ~ 18V
• Mounting Type: Through Hole
• Package / Case: 14-CDIP (0.300", 7.62mm)
• Accuracy %: 0.25%
• Bandwidth: 200kHz
• Supply Current: 2.2mA
• Power Dissipation Pd: 108mW
• Supply Voltage Range: ± 3V To ± 18V
• Digital Ic Case Style: DIP
• No. Of Pins: 14
• Input Type: RMS
• Module Type: Converter
• Output Type: DC
• Voltage, Supply: ± 18 VDC
• For Use With: AD637-EVALZ - BOARD EVALUATION FOR AD637
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD637
FUNCTIONAL DESCRIPTION
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
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 V
current I
the squarer/divider, which has the transfer function
The output current of the squarer/divider I
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 I
to provide the denominator current I
is returned to the squarer/divider to complete the implicit rms
computation
and
BUFF OUT
V
V
I
I
4
4
OUT
BUFF IN
rms
=
=
1
IN
Avg
I
by the active rectifier A1, A2. I
I
1
=
, which can be ac or dc, is converted to a unipolar
3
V
2
=
V
IN
Avg
⎡
⎢
⎣
IN
I
4
I
14
13
. The output of this filter amplifier is used by A3
1
1
4
rms
2
⎡
⎢
⎢
⎣
⎤
⎥
⎦
V
=
V
ABSOLUTE VALUE VOLTAGE –
12k Ω
ΙΝ
rms
I
1
2
r
CURRENT CONVERTER
ms
⎤
⎥
⎥
⎦
24k Ω
6k Ω
A1
A5
3
, which equals Avg I
1
drives one input of
4
drives A4, which
6k Ω
AMPLIFIER
BUFFER
I
1
A2
Figure 4. Simplified Schematic
4
and
Rev. G | Page 8 of 20
SQUARER/DIVIDER
ONE QUADRANT
Q2
Q1
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 I
now equal to I
The denominator current can also be supplied externally
by providing a reference voltage, V
operates identically to the rms case except that I
proportional to V
and
This is the mean square of the input signal.
Q3
V
I =
I =
I =
4
4
4
O
Q4
=
Avg
I
I
I
V
1
V
1
4
2
DEN
IN
I
A3
4
2
I
4
I
, giving
1
3
2
125 Ω
REF
. Therefore,
FILTER/AMPLIFIER
Q5
A4
24k Ω
I
3
AD637
REF
24k Ω
BIAS
, to Pin 6. The circuit
11
10
8
9
7
3
5
6
4
3
+V
dB
OUT
COM
DEN
INPUT
OUTPUT
OFFSET
CAV
RMS
CS
–V
is now
OUT
S
S
3
is