AD8028 datasheet(21/24 Pages) AD

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AD8027/AD8028

Rev. B | Page 21 of 24

Band-Pass Filter

In communication systems, active filters are used extensively in

signal processing. The AD8027/AD8028 is an excellent choice

for active filter applications. In realizing this filter, it is impor-

tant that the amplifier has a large signal bandwidth of at least

10× the center frequency, fO. Otherwise, a phase shift can occur

in the amplifier, causing instability and oscillations.

In the schematic shown in Figure 62, the AD8027/AD8028 is

configured as a 1 MHz band-pass filter. The target specifications

are fO = 1 MHz and a –3 dB pass band of 500 kHz. Start the

design by selecting the following: fO, Q, C1, and R4. Then using

the equations shown below, calculate the remaining variables.

The test data shown in Figure 63 indicates that this design

yielded a filter response with a center frequency fO = 1 MHz and

a bandwidth of 450 kHz.

(MHz)

Band

Pass

k = 2πfOC1

C2 = 0.5C1

R1 = 2/k, R2 = 2/(3k), R3 = 4/k

H = 1/3(6.5 – 1/Q)

R5 = R4/(H – 1)

–5

0.1

µF

0.1

µF

523

Ω

523

Ω

500pF

1000pF

634

Ω

VOUT

316

Ω

105

Ω

VIN

SELECT

AD8027/

AD8028

–

03327-A-061

Figure 62. Band-Pass Filter Schematic

0.1

CH1 S21 LOG

5dB/REF 6.342dB

1:6.3348dB 1.00 000MHz

FREQUENCY – MHz

03327-A-062

Figure 63. Band-Pass Filter Response

Design Tools and Technical Support

Analog Devices is committed to simplifying the design process

by providing technical support and online design tools. We offer

technical support via free evaluation boards, sample ICs, inter-

active evaluation tools, data sheets, spice models, application

notes, phone and email support, all of which are available at

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