ad704ar Analog Devices, Inc., ad704ar Datasheet - Page 9

• Manufacturer Part Number: ad704ar
• Description: Quad Picoampere Input Current Bipolar Op Amp
• Manufacturer: Analog Devices, Inc.

The 1 Hz, 4-pole active filter offers dc precision with a minimum
of components and cost. The low current noise, I
allow the use of 1 MΩ resistors without sacrificing the 1 µV/°C
drift of the AD704. This means lower capacitor values may be
used, reducing cost and space. Furthermore, since the AD704’s
I
most applications do not require the use of the normal balancing
resistor (with its stability capacitor). Adding the optional balancing
resistor enhances performance at high temperatures, as shown in
Figure 5. Table II gives capacitor values for several common low
pass responses.
Desired Low
Pass Response
Bessel
Butterworth
0.1 dB Chebychev
0.2 dB Chebychev
0.5 dB Chebychev
1.0 dB Chebychev
Specified values are for a –3 dB point of 1.0 Hz. For other frequencies, simply scale capacitors C1 through C4 directly; i.e., for 3 Hz Bessel response, C1 = 0.0387 µF,
B
C2 = 0.0357 µF, C3 = 0.0533 µF, C4 = 0.0205 µF.
is as low as its I
OS
, over most of the MIL temperature range,
Section 1
Frequency
(Hz)
1.43
1.00
0.648
0.603
0.540
0.492
Table II. 1 Hz, 4-Pole Low-Pass Filter Recommended Component Values
Q
0.522
0.541
0.619
0.646
0.705
0.785
OS
, and I
Section 2
Frequency
(Hz)
1.60
1.00
0.948
0.941
0.932
0.925
B
Q
0.806
1.31
2.18
2.44
2.94
3.56
–120
–180
180
120
–60
60
0
–40
C1
( F)
0.116
0.172
0.304
0.341
0.416
0.508
WITHOUT OPTIONAL
BALANCE RESISTOR, R3
0
TEMPERATURE – C
WITH OPTIONAL
BALANCE RESISTOR, R3
( F)
0.107
0.147
C2
0.198
0.204
0.209
0.206
+40
+80
C3
( F)
0.160
0.416
0.733
0.823
1.00
1.23
AD704
+120
C4
( F)
0.0616
0.0609
0.0385
0.0347
0.0290
0.0242