Datasheet

AD8027/AD8028
Rev. C | Page 22 of 24
BAND-PASS FILTER
In communication systems, active filters are used extensively in
signal processing. The AD8027/AD8028 are excellent choices
for active filter applications. In realizing this filter, it is impor-
tant that the amplifier have a large signal bandwidth of at least
10× the center frequency, f
O
. Otherwise, a phase shift can occur
in the amplifier, causing instability and oscillations.
In
Figure 62, the AD8027/AD8028 part is configured as a
1 MHz band-pass filter. The target specifications are f
O
= 1 MHz
and a −3 dB pass band of 500 kHz. To start the design, select f
O
,
Q, C1, and R4. Then use the following equations to calculate the
remaining variables:
(MHz)
(MHz)
PassBand
f
Q
O
=
k = 2πf
O
C1
C2 = 0.5C1
R1 = 2/k, R2 = 2/(3k), R3 = 4/k
H = 1/3(6.5 – 1/Q)
R5 = R4/(H – 1)
+5
–5
C3
0.1
μ F
C4
0.1
μ F
R4
523
Ω
R5
523
Ω
C2
500pF
C1
1000pF
R3
634
Ω
V
OUT
R1
316
Ω
R2
105
Ω
V
IN
SELECT
AD8027/
AD8028
+
–
03327-A-061
Figure 62. Band-Pass Filter Schematic
The test data shown in Figure 63 indicates that this design
yields a filter response with a center frequency of f
O
= 1 MHz,
and a bandwidth of 450 kHz.
0.1
CH1 S21 LOG 5dB/REF 6.342dB 1:6.3348dB 1.00 000MHz
1
FREQUENCY – MHz
10
1
03327-A-062
Figure 63. Band-Pass Filter Response
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available at
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