ADL5382 datasheet(15/28 Pages) AD

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ADL5382

Rev. 0 | Page 15 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 the 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 (the

recommended value is 33 nH, Coilcraft 0603CS-33NX) 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

0603 inductor has a 600 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 42

shows the RF input configuration.

RF INPUT

RFIN

ETC1-1-13

33nH

RFIP

1000pF

Figure 42. RF Input

The differential RF port return loss is characterized as shown in

Figure 43.

–10

–12

–14

–16

–18

–20

–22

–24

0.7

0.9

1.1

1.5

1.7

1.3

1.9

2.1

2.3

2.5

2.7

2.9

FREQUENCY (GHz)

Figure 43. 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 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

370 MHz. Figure 44 shows the baseband output configuration.

QHI

QLO

IHI

ILO

QHI

QLO

IHI

ILO

Figure 44. Baseband Output Configuration

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