AD711SH Datasheet, PDF (12/16 Pages) Analog Devices – Precision, Low Cost, High Speed, BiFET Op Amp

AD711
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 ϫ 10^–15 and 5.9276 ϫ
10^–15 farad-seconds. Each FDNR active network provides a
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.
+15V
0.1␮F
V_IN
A1
AD711
0.001␮F _2800⍀
6190⍀
6490⍀
6190⍀ 2800⍀
4.9395E^–15 5.9276E^–15 5.9276E^–15 4.9395E^–15
0.1␮F
A
B
C
D
–15V
*
*
*
*
100k⍀
0.001
␮F
124k⍀
*_{SEE TEXT}
+15V
0.1␮F
A2
AD711
0.1␮F
–15V
V_OUT
4.99k⍀
4.99k⍀
Figure 17. 9-Pole Chebychev Filter
+15V
0.1␮F
0.001␮F
R
1/2
AD712
1/2
AD712
0.001␮F
0.1␮F
–15V
1k⍀
R: 24.9k⍀ FOR 4.9395E^–15
29.4k⍀ FOR 5.9276E^–15
4.99k⍀
Figure 18. FDNR for 9-Pole Chebychev Filter
Figure 19. High Frequency Response for 9-Pole
Chebychev Filter
–12–
REV. E