AD706
R1
1M
INPUT
R2
1M
3
C1
+
1/2
R3
1M
R4
1M
C4
0.1 F
–V
S
R5
2M
C5
0.01 F
OPTIONAL BALANCE
RESISTOR NETWORKS*
C3
+V
S
0.1 F
5
+
8
C2
2
AD706
–
4
1
1/2
AD706
6
7
OUTPUT
*WITHOUT
THE NETWORK,
PINS 1 AND 2, AND 6 AND 7
OF THE AD706 ARE TIED
TOGETHER.
CAPACITORS C1 AND C2
ARE SOUTHERN ELECTRONICS
MPCC, POLYCARB 5%, 50V
–
R6
2M
C6
0.01 F
Figure 7. 1 Hz, 4-Pole Active Filter
1 Hz, 4-Pole, Active Filter
Figure 7 shows the AD706 in an active filter application. An
important characteristic of the AD706 is that both the input bias
current, input offset current, and their drift remain low over
most of the op amp’s rated temperature range. Therefore, for
most applications, there is no need to use the normal balancing
resistor. Adding the balancing resistor enhances performance at
high temperatures, as shown by Figure 8.
OFFSET VOLTAGE OF FILTER CIRCUIT (RTI) – V
180
120
WITHOUT OPTIONAL
BALANCE RESISTOR, R3
60
0
WITH OPTIONAL BALANCE
RESISTOR, R3
–60
–120
–180
–40
0
40
80
TEMPERATURE – C
120
Figure 8. V
OS
vs. Temperature Performance
of the 1 Hz Filter
Table II. 1 Hz, 4-Pole, Low Pass Filter Recommended Component Values
Desired Low
Pass Response
Bessel
Butterworth
0.1 dB Chebychev
0.2 dB Chebychev
0.5 dB Chebychev
1.0 dB Chebychev
Section 1
Frequency
(Hz)
1.43
1.00
0.648
0.603
0.540
0.492
Q
0.522
0.541
0.619
0.646
0.705
0.785
Section 2
Frequency
(Hz)
1.60
1.00
0.948
0.941
0.932
0.925
Q
0.806
1.31
2.18
2.44
2.94
3.56
C1
( F)
0.116
0.172
0.304
0.341
0.416
0.508
C2
( F)
0.107
0.147
0.198
0.204
0.209
0.206
C3
( F)
0.160
0.416
0.733
0.823
1.00
1.23
C4
( F)
0.0616
0.0609
0.0385
0.0347
0.0290
0.0242
NOTE
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,
C2 = 0.0357
µF,
C3 = 0.0533
µF,
C4 = 0.0205
µF.
–8–
REV. E
AD [ ANALOG DEVICES ]
