AD8027ARTZ-R21 datasheet(23/25 Pages) AD

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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, fO. 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 fO = 1 MHz

and a −3 dB pass band of 500 kHz. To start the design, select fO,

Q, C1, and R4. Then use the following equations to calculate the

remaining variables:

(MHz)

Pass

Band

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

500pF

1000pF

634

VOUT

316

105

VIN

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 fO = 1 MHz,

and a bandwidth of 450 kHz.

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, Inc. (ADI) is committed to simplifying the

design process by providing technical support and online

design tools. ADI offers technical support via free evaluation

boards, sample ICs, interactive evaluation tools, data sheets,

spice models, application notes, and phone and email support

available at www. analog.com.

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