AD8052 datasheet(18/24 Pages) AD

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AD8051/AD8052/AD8054

Rev. G | Page 18 of 24

AD8054

1kΩ

2kΩ

3kΩ

50pF

VIN

BAND-PASS

FILTER OUTPUT

LAYOUT CONSIDERATIONS

The specified high speed performance of the AD8051/AD8052/

AD8054 requires careful attention to board layout and

component selection. Proper RF design techniques and low

parasitic component selection are necessary.

The PCB should have a ground plane covering all unused

portions of the component side of the board to provide a low

impedance path. The ground plane should be removed from the

area near the input pins to reduce parasitic capacitance.

Figure 46. 2 MHz Biquad Band-Pass Filter Using AD8054

Chip capacitors should be used for supply bypassing. One end

should be connected to the ground plane and the other within

3 mm of each power pin. An additional large (4.7 μF to 10 μF)

tantalum electrolytic capacitor should be connected in parallel,

but not necessarily so close, to supply current for fast, large

signal changes at the output.

The frequency response of the circuit is shown in Figure 47.

FREQUENCY (Hz)

–10

–20

–30

–40

10k

100k

10M

100M

The feedback resistor should be located close to the inverting

input pin to keep the parasitic capacitance at this node to a

minimum. Parasitic capacitance of less than 1 pF at the

inverting input can significantly affect high speed performance.

Stripline design techniques should be used for long signal traces

(greater than about 25 mm). These should be designed with a

characteristic impedance of 50 Ω or 75 Ω and be properly

terminated at each end.

ACTIVE FILTERS

Figure 47. Frequency Response of 2 MHz Band-Pass Biquad Filter

Active filters at higher frequencies require wider bandwidth op

amps to work effectively. Excessive phase shift produced by

lower frequency op amps can significantly affect active filter

performance.

A/D AND D/A APPLICATIONS

Figure 48 is a schematic showing the AD8051 used as a driver

for an AD9201, a 10-bit, 20 MSPS, dual A/D converter. This

converter is designed to convert I and Q signals in communications

systems. In this application, only the I channel is being driven.

The I channel is enabled by applying a logic high to SELECT

(Pin 13).

Figure 46 shows an example of a 2 MHz biquad bandwidth filter

that uses three op amps of an AD8054. Such circuits are

sometimes used in medical ultrasound systems to lower the

noise bandwidth of the analog signal before A/D conversion.

AD8051

The

is running from a dual supply and is configured

for a gain of +2. The input signal is terminated in 50 Ω and the

output is 2 V p-p, which is the maximum input range of the

Note that the unused amplifier’s inputs should be tied to

ground.

AD9201. The 22 Ω series resistor limits the maximum current

that flows and helps to lower the distortion of the A/D converter.

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