ADL5387ACPZ-R71 datasheet(16/28 Pages) AD

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ADL5387

Rev. 0 | Page 16 of 28

RF INPUT

The RF inputs have a differential input impedance of

approximately 50 Ω. For optimum performance, the RF port

should be driven differentially through a balun. The recommended

balun is M/A-COM ETC1-1-13. The RF inputs to the device

should be ac-coupled with 1000 pF capacitors. Ground-referenced

choke inductors must also be connected to RFIP and RFIN

(recommended value = 120 nH, Coilcraft 0402CS-R12XJL) for

appropriate biasing. Several important aspects must be taken

into account when selecting an appropriate choke inductor for

this application. First, the inductor must be able to handle the

approximately 40 mA of standing dc current being delivered

from each of the RF input pins (RFIP, RFIN). (The suggested

0402 inductor has a 50 mA current rating). The purpose of the

choke inductors is to provide a very low resistance dc path to

ground and high ac impedance at the RF frequency so as not to

affect the RF input impedance. A choke inductor that has a self-

resonant frequency greater than the RF input frequency ensures

that the choke is still looking inductive and therefore has a more

predictable ac impedance (jωL) at the RF frequency. Figure 48

shows the RF input configuration.

RF INPUT

RFIN

ETC1-1-13

120nH

RFIP

1000pF

Figure 48. RF Input

The differential RF port return loss has been characterized as

shown in Figure 49.

–10

–12

–14

–16

–18

–20

–22

–24

–26

–28

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

FREQUENCY (GHz)

Figure 49. Differential RF Port Return Loss

BASEBAND OUTPUTS

The baseband outputs QHI, QLO, IHI, and ILO are fixed

impedance ports. Each baseband pair has a 50 Ω differential

output impedance. The outputs can be presented with differential

loads as low as 200 Ω (with some degradation in linearity and

gain) or high impedance differential loads (500 Ω or greater

impedance yields the same excellent linearity) that is typical of

an ADC. The TCM9-1 9:1 balun converts the differential IF

output to single-ended. When loaded with 50 Ω, this balun

presents a 450 Ω load to the device. The typical maximum

linear voltage swing for these outputs is 2 V p-p differential.

The bias level on these pins is equal to VPOS − 2.8 V. The

output 3 dB bandwidth is 240 MHz. Figure 50 shows the

baseband output configuration.

QHI

QLO

IHI

ILO

QHI

QLO

IHI

ILO

Figure 50. Baseband Output Configuration

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