AD712

REV. B

–14–

+15V

0.001 F

100k

0.1 F

0.1 F

A2

AD711

–15V

+15V

0.1 F

0.1 F

A1

AD711

–15V

*

D

*

C

*

B

*

A

2800

6190

6490

6190

2800

0.001 F

124k

4.99k

4.99k

Figure 40. 9-Pole Chebychev Filter

9-POLE CHEBYCHEV FILTER

Figure 40 shows the AD712 and its dual counterpart, the

AD711, as a 9-pole Chebychev filter using active frequency

dependent negative resistors (FDNR). With a cutoff frequency

of 50 kHz and better than 90 dB rejection, it may be used as an

antialiasing filter for a 12-bit Data Acquisition System with

100 kHz throughput.

As shown in Figure 40, the filter is comprised of four FDNRs

(A, B, C, D) having values of 4.9395

10

10

two-pole response; for a total of 8 poles. The 9th pole consists

of a 0.001

µF capacitor and a 124 kΩ resistor at Pin 3 of ampli-

fier A2. Figure 41 depicts the circuits for each FDNR with the

proper selection of R. To achieve optimal performance, the

0.001

µF capacitors must be selected for 1% or better matching

and all resistors should have 1% or better tolerance.

+15V

0.001 F

4.99k

0.1 F

0.1 F

1/2

AD712

–15V

1.0k

R:

24.9k

29.4k

1/2

AD712

0.001 F

R

Figure 41. FDNR for 9-Pole Chebychev Filter

REF 5.0 dBm

10 dB/DIV

RANGE –5.0 dBm

MARKER 96 800.0 Hz

–90 dBm

START.0 Hz

RBW 300 Hz

STOP 200 000.0 Hz

ST 69.6 SEC

VBW 30 Hz

Figure 42. High Frequency Response for 9-Pole

Chebychev Filter