AD712
+15V
0.1F
+15V
0.1F
V
IN
0.001F
2800⍀
6190⍀
6490⍀
6190⍀
2800⍀
A1
AD711
A2
AD711
V
–15
–15
–15
–15
OUT
4.9395E
5.9276E
5.9276E
4.9395E
0.1F
A
B
C
D
0.1F
4.99k⍀
4.99k⍀
–15V
*
*
*
*
–15V
100k⍀
0.001F
124k⍀
SEE TEXT
*
Figure 40. 9-Pole Chebychev Filter
9-POLE CHEBYCHEV FILTER
REF 5.0 dBm
10 dB/DIV
MARKER 96 800.0 Hz
RANGE –5.0 dBm –90 dBm
Figure 40 shows the AD712 and its dual counterpart, the
AD711, 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
antialiasing filter for a 12-bit Data Acquisition System with
100 kHz throughput.
As shown in Figure 40, 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
two-pole response; for a total of 8 poles. The 9th pole consists
of a 0.001 µF capacitor and a 124 kΩ resistor at Pin 3 of ampli-
fier A2. Figure 41 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.
STOP 200 000.0 Hz
ST 69.6 SEC
START.0 Hz
RBW 300 Hz
VBW 30 Hz
Figure 42. High Frequency Response for 9-Pole
Chebychev Filter
+15V
0.1F
0.001F
1/2
AD712
R
0.1F
1/2
AD712
0.001F
–15V
1.0k⍀
4.99k⍀
–15
R: 24.9k⍀ FOR 4.9395E
–15
29.4k⍀ FOR 5.9276E
Figure 41. FDNR for 9-Pole Chebychev Filter
–14–
REV. B
ADI [ ADI ]
