AD713
Rev. F | Page 15 of 20
1/4
AD713
A1
+V
S
V
IN
R3
10kΩ
R4
30kΩ
C1
1000pF
C3
33pF
HIGH
PASS
OUTPUT
R5
30kΩ
+
1µF
4
2
3
1
1/4
AD713
A2
6
5
7
1/4
AD713
A3
9
10
8
AD7528
V
DD
DAC B1
R
F
1819202
1
5
61615
17
14 7
DB0 TO
DB7
DATA 1
DAC A/
DACB
WRCS
DAC A1
R
S
AD7528
V
DD
20182
1
5
61615
17
14 7
DB0 TO
DB7
DATA 2
DAC A/
DAC B
WRCS
DAC A2
R1
4
4
C2
1000pF
1/4
AD713
A4
13
12
14
DAC B2
R2
–V
S
BAND PASS
OUTPUT
LOW PASS
OUTPUT
1µF
11
+
CIRCUIT EQUATIONS
C
1
= C
2
, R
1
= R
2
, R
4
= R
5
f
C
=
1
2π R
1
C
1
A
O
= –
R
F
R
S
256 × (DAC LADDER RESISTANCE)
DAC DIGITAL CODE
DAC EQUIVALENT RESISTANCE EQUALS
Q = ×
R
3
R
4
R
F
R
FBB1
00824-046
Figure 44. A Programmable State Variable Filter Circuit
GIC AND FDNR FILTER APPLICATIONS
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).
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 (V
S
= ±15 V) with no
overload at any internal nodes.
The filter of Figure 47 can be scaled for any center frequency by
using the following formula:
R
f
C
π
2
11.1
=
where all resistors and capacitors scale equally. Resistors R3 to
R8 should not be greater than 2 k in value to prevent parasitic
oscillations caused by the amplifier’s input capacitance.
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.
0
–10
–20
–30
–40
–50
–60
–70
0 102030405060708090100
FREQUENCY (MHz)
OUTPUT AMPLITUDE (dBm)
00824-048
OUTPUT AMPLITUDE (dBm)
0
–1
–2
–3
–4
–5
16 18 20
FREQUENCY (MHz)
22 24
Figure 45. Output Amplitude vs. Frequency of 1/3 Octave Filter
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
10k 100k 1M
FREQUENCY (MHz)
RELATIVE OUTPUT AMPLITUDE (dB)
00824-049
3
2
1
0
–1
200 500 1k 2k
µs dB
5k 10k 20k
200 500 1k 2k 5k 10k 20k
18
19
20
21
22
OUTPUT AMPLITUDE
GROUP DELAY
Figure 46. Relative Output Amplitude vs. Frequency of Antialiasing Filter
