Datasheet
REV. E
AD711
–12–
+15V
–15V
0.1F
0.1F
A1
AD711
V
IN
V
OUT
+15V
–15V
0.1F
0.1F
A2
AD711
A
*
B
*
C
*
D
*
0.001F
4.9395E
–15
5.9276E
–15
5.9276E
–15
4.9395E
–15
2800 6190 6490 6190
0.001
F
100k
124k
2800
*
SEE TEXT
4.99k
4.99k
Figure 17. 9-Pole Chebychev Filter
+15V
–15V
0.1F
0.1F
1/2
AD712
1/2
AD712
0.001F
0.001F
R
1k
4.99k
R: 24.9k FOR 4.9395E
–15
29.4k FOR 5.9276E
–15
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
–15
and 5.9276 ⫻
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.