REV. E

AD711

–12–

+15V

–15V

0.1 F

0.1 F

A1

AD711

+15V

–15V

0.1 F

0.1 F

A2

AD711

A

*

B

*

C

*

D

*

0.001 F

2800

6190

6490

6190

0.001

F

100k

124k

2800

*SEE TEXT

4.99k

4.99k

Figure 17. 9-Pole Chebychev Filter

+15V

–15V

0.1 F

0.1 F

1/2

AD712

1/2

AD712

0.001 F

0.001 F

R

1k

4.99k

R: 24.9k

29.4k

Figure 18. FDNR for 9-Pole Chebychev Filter

Figure 19. High Frequency Response for 9-Pole

Chebychev Filter

9-POLE CHEBYCHEV FILTER

Figure 17 shows the AD711 and its dual counterpart, the AD712,

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 anti-aliasing

filter for a 12-bit data acquisition system with 100 kHz throughput.

As shown in Figure 17, the filter is comprised of four FDNRs (A,

B, C, D) having values of 4.9395

10

10

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

0.001

mF capacitor and a 124 kW resistor at Pin 3 of amplifier A2.

Figure 18 depicts the circuits for each FDNR with the proper

selection of R. To achieve optimal performance, the 0.001

mF

capacitors must be selected for 1% or better matching and all

resistors should have 1% or better tolerance.