Datasheet
REV. E–8–
AD706
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
+
–
C4
C3
0.1F
+V
S
OPTIONAL BALANCE
RESISTOR NETWORKS*
1/2
AD706
1/2
AD706
INPUT
C1
C2
+
–
R1
1M
0.1F
R2
1M
R3
1M
R4
1M
–V
S
R5
2M
C5
0.01F
3
2
4
1
5
6
7
8
R6
2M
C6
0.01F
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.
TEMPERATURE – C
180
–40 0 40
60
120
0
–60
–120
–180
OFFSET VOLTAGE OF FILTER CIRCUIT (RTI) – V
80 120
WITHOUT OPTIONAL
BALANCE RESISTOR, R3
WITH OPTIONAL BALANCE
RESISTOR, R3
Figure 8. V
OS
vs. Temperature Performance
of the 1 Hz Filter
Table II. 1 Hz, 4-Pole, Low Pass Filter Recommended Component Values
Section 1 Section 2
Desired Low Frequency Frequency C1 C2 C3 C4
Pass Response (Hz) Q (Hz) Q (F) (F) (F) (F)
Bessel 1.43 0.522 1.60 0.806 0.116 0.107 0.160 0.0616
Butterworth 1.00 0.541 1.00 1.31 0.172 0.147 0.416 0.0609
0.1 dB Chebychev 0.648 0.619 0.948 2.18 0.304 0.198 0.733 0.0385
0.2 dB Chebychev 0.603 0.646 0.941 2.44 0.341 0.204 0.823 0.0347
0.5 dB Chebychev 0.540 0.705 0.932 2.94 0.416 0.209 1.00 0.0290
1.0 dB Chebychev 0.492 0.785 0.925 3.56 0.508 0.206 1.23 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.