AD712AH Analog Devices, AD712AH Datasheet - Page 14

• Manufacturer Part Number: AD712AH
• Description: Dual Precision/ Low Cost/ High Speed/ BiFET Op Amp
• Manufacturer: Analog Devices

AD712
9-POLE CHEBYCHEV FILTER
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
10
two-pole response; for a total of 8 poles. The 9th pole consists
of a 0.001 F capacitor and a 124 k 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 F capacitors must be selected for 1% or better matching
and all resistors should have 1% or better tolerance.
–15
R: 24.9k
farad-seconds. Each FDNR active network provides a
Figure 41. FDNR for 9-Pole Chebychev Filter
29.4k
V
IN
FOR 4.9395E
FOR 5.9276E
AD712
1/2
AD711
–15
–15
A1
+15V
–15V
0.1 F
0.1 F
1.0k
R
4.99k
0.001 F
0.001 F
0.001 F
100k
10
4.9395E
–15
2800
AD712
and 5.9276
–15
+15V
1/2
–15V
A
*
Figure 40. 9-Pole Chebychev Filter
0.1 F
0.1 F
5.9276E
*
6190
SEE TEXT
–15
B
*
5.9276E
6490
–14–
–15
C
*
4.9395E
6190
Figure 42. High Frequency Response for 9-Pole
Chebychev Filter
–15
D
*
REF 5.0 dBm
10 dB/DIV
START.0 Hz
RBW 300 Hz
0.001 F
2800
RANGE –5.0 dBm
124k
VBW 30 Hz
AD711
MARKER 96 800.0 Hz
A2
+15V
–15V
STOP 200 000.0 Hz
0.1 F
0.1 F
ST 69.6 SEC
–90 dBm
4.99k
4.99k
V
OUT
REV. B