Datasheet

AD712
Rev. G | Page 18 of 20
+15V
0.001µF
100kΩ
0.1µF
0.1µF
–15V
+15
V
0.1µF
0.1µF
–15V
*
D
*
C
*
B
*
A
2800Ω 6190Ω 6490Ω 6190Ω 2800Ω
V
IN
0.001µF
124kΩ
4.99kΩ
4.99kΩ
V
OUT
4.9395E
–15
5.9276E
–15
5.9276E
–15
4.9395E
–15
*
SEE TEXT
A1
AD711
A2
AD711
++++
+
–
+
–
00823-050
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
(A, B, C, D) having values of 4.9395 × 10
−15
and 5.9276 × 10
–15
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 F 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
R: 24.9kΩ FOR 4.9395E
–15
29.4kΩ FOR 5.9276E
–15
+
0
0823-051
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 SECVBW 30Hz
00823-052
Figure 52. High Frequency Response for 9-Pole Chebychev Filter