ADL5206ACPZ-R7 datasheet(24/25 Pages) AD

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ADL5206

Data Sheet

Rev. 0 | Page 24 of 25

ADC INTERFACING

A typical data acquisition system using the ADL5206 together

with an antialiasing filter and an ADC is shown in Figure 63.

The main role of the filter after the amplifier is for attenuating

the broadband noise and out of band harmonics generated by

the amplifier. Component values for a 500 MHz acquisition

bandwidth are listed in Table 13. Without this filter, the out

of band noise and distortion components alias back into the

Nyquist band, resulting in a reduction of signal-to-noise ratio.

The design of the filter preceding the ADL5206 amplifier is

more specific to the system rejection requirements for the

acquisition system.

R1A

R1B

L3A

L1A

L3B

L1B

VCM

C2B

C2A

ADC

AMP

FILTER

Figure 63. ADC Interface (One of Two Channels Shown)

Table 13. Component Values for a 500 MHz Acquisition System

Component

Value

Description/Comments

Amplifier

½ ADL5206

One channel

L1A, L1B

22 nH

Q ≥ 50 at 500 MHz

C2A, C2B

6.8 pF

Final value depends on PCB

parasitics

L3A, L3B

22 nH

Q ≥ 50 at 500 MHz

1.5 pF

Final value depends on PCB

parasitics

R1A, R1B

10 Ω

Not applicable

ADC

½ AD9680

One channel, input impedance set

to 100 Ω

NOISE FIGURE vs. GAIN SETTING

Because of the architecture of the ADL5206, the noise figure

does not degrade significantly for the first 10 dB of gain reduction

from the maximum gain setting. The noise figure increases by

0.5 dB only during the first 10 dB of gain reduction. The noise

figure changes by 7 dB over the 30 dB gain range.

GAIN (dB)

ADL5206

AT 700MHz 5V

HIGH PERFORMANCE

REGULAR ATTENUATOR

AMPLIFIER CASCADE

–10

–5

30 32

Figure 64. Noise Figure vs. Gain

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