AD712

Rev. G | Page 18 of 20

+15V

0.001µF

100kΩ

0.1µF

0.1µF

–15V

+15V

0.1µF

0.1µF

–15V

*

D

*

C

*

B

*

A

2800Ω

6190Ω

6490Ω

6190Ω

2800Ω

0.001µF

124kΩ

4.99kΩ

4.99kΩ

A1

AD711

A2

AD711

+

+

+

+

+

–

+

–

Figure 50. 9-Pole Chebychev Filter

9-POLE CHEBYCHEV FILTER

Figure 50 and Figure 51 show the AD712 and its dual

counterpart, the AD711, as a 9-pole Chebychev filter using

active frequency dependent negative resistors (FDNRs). With a

cutoff frequency of 50 kHz and better than 90 dB rejection, it

can be used as an antialiasing filter for a 12-bit data acquisition

system with 100 kHz throughput.

As shown in Figure 50, the filter is comprised of four FDNRs

farad-seconds. Each FDNR active network provides a two-pole

response for a total of eight poles. The ninth pole consists of a

0.001 μF capacitor and a 124 kΩ resistor at Pin 3 of Amplifier A2.

Figure 51 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

0.001µF

4.99kΩ

0.1µF

0.1µF

–15V

1.0kΩ

0.001µF

R

1/2

AD712

+

–

1/2

AD712

+

Figure 51. FDNR for 9-Pole Chebychev Filter

REF 5.0dBm

10dB/DIV

RANGE –5.0dBm

MARKER 96 800.0Hz

–90dBm

START.0Hz

RBW 300Hz

STOP 200 000.0Hz

ST 69.6 SEC

VBW 30Hz

Figure 52. High Frequency Response for 9-Pole Chebychev Filter