AD713
R5
30kΩ
+V
4
S
1µF
C1
1000pF
C2
1000pF
R4
CIRCUIT EQUATIONS
C3
33pF
30kΩ
+
R3
10kΩ
2
3
C
= C , R = R , R = R
2 1 2 4 5
1
1
6
5
9
13
12
A1
HIGH
LOW PASS
OUTPUT
7
8
14
A2
PASS
A3
A4
1/4
AD713
OUTPUT
1
10
1/4
AD713
f
=
C
11
2π R
C
1
1/4
AD713
1/4
1
AD713
+
1µF
R
R
R
F
3
Q =
×
V
V
DD
DD
R
4
FBB1
2
20
19
18
4
2
18
20
–V
S
17
4
17
BAND PASS
OUTPUT
AD7528
DAC A1
R
F
A = –
O
1
5
1
5
R
V
S
IN
DAC B1
DAC A2
R1
DAC B2
R2
AD7528
R
R
S
F
15
16
6
15
16
6
14
7
14
7
DAC EQUIVALENT RESISTANCE EQUALS
256 × (DAC LADDER RESISTANCE)
DAC DIGITAL CODE
DB0 TO
DB0 TO
DB7
DB7
CS
WR DAC A/
DACB
CS
WR DAC A/
DAC B
DATA 1
DATA 2
Figure 44. A Programmable State Variable Filter Circuit
0
GIC AND FDNR FILTER APPLICATIONS
0
–1
–2
–3
–4
The closely matched and uniform ac characteristics of the AD713
make it ideal for use in generalized impedance converter (GIC)/
gyrator and frequency dependent negative resistor (FDNR)
filter applications. Figure 47 and Figure 48 show the AD713
used in two typical active filters. The first shows a single AD713
simulating two coupled inductors configured as a one-third
octave band-pass filter. A single section of this filter meets
ANSI Class II specifications and handles a 7.07 V rms signal
with <0.002% THD (20 Hz to 20 kHz).
–10
–20
–30
–5
16 18 20 22 24
–40
–50
–60
FREQUENCY (MHz)
Figure 48 shows a seven-pole antialiasing filter for a 2× over-
sampling (88.2 kHz) digital audio application. This filter has
<0.05 dB pass-band ripple and 19.8 ꢀs 0.3 ꢀs delay, at dc to
20 kHz, and handles a 5 V rms signal (VS = 15 V) with no
overload at any internal nodes.
–70
0
10
20
30
40
50
60
70
80
90
100
FREQUENCY (MHz)
Figure 45. Output Amplitude vs. Frequency of 1/3 Octave Filter
3
OUTPUT AMPLITUDE
2
The filter of Figure 47 can be scaled for any center frequency by
using the following formula:
0
–10
–20
–30
–40
–50
1
0
–1
1.11
2πRC
200 500 1k 2k
5k 10k 20k
fC
=
18
19
20
21
22
GROUP DELAY
where all resistors and capacitors scale equally. Resistors R3 to
R8 should not be greater than 2 kꢁ in value to prevent parasitic
oscillations caused by the amplifier’s input capacitance.
–60
–70
–80
200 500 1k 2k
5k 10k 20k
If this is not practical, add small lead capacitances (10 pF to
20 pF) across R5 and R6. Figure 45 and Figure 46 show the
output amplitude vs. frequency of these filters.
–90
–100
–110
–120
10k
100k
1M
FREQUENCY (MHz)
Figure 46. Relative Output Amplitude vs. Frequency of Antialiasing Filter
Rev. F | Page 15 of 20
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