REV. G

–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

0.1 F

+VS

OPTIONAL BALANCE

RESISTOR NETWORKS*

1/2

AD706

1/2

AD706

INPUT

C1

C2

+

–

R1

1M

0.1 F

R2

1M

R3

1M

R4

1M

–VS

R5

2M

C5

0.01 F

3

2

4

1

5

6

7

8

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.

TEMPERATURE – C

180

–40

0

40

60

120

0

–60

–120

–180

80

120

WITHOUT OPTIONAL

BALANCE RESISTOR, R3

WITH OPTIONAL BALANCE

RESISTOR, R3

Figure 8. VOS 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.