AD637JQ Analog Devices Inc, AD637JQ Datasheet - Page 12

• 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

dB CALIBRATION
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 V
accordingly.
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
C
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.
AV1
, in this circuit 0.5 s/µF of C
AV
. This circuit permits a 20:1
IN
and R1
Rev. G | Page 15 of 20
If the frequency of interest is below 1 Hz, or if the value of
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.
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
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 C
If the averaging capacitor is included on both IC1 and IC2, the
output is
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.
AV
V
is added to IC1 in this configuration, the output is
O
V
V
X
X
=
2
2
+
+
V
V
V
X
Y
Y
2
2
2
+
V
Y
2
AD637