AD8361ART datasheet(23/24 Pages) AD

23 / 24 page

AD8361

Rev. C | Page 23 of 24

Problems caused by impedance mismatch may arise using the

evaluation board to examine the AD8361 performance. One

way to reduce these problems is to put a coaxial 3 dB attenuator

on the RFIN SMA connector. Mismatches at the source, cable,

and cable interconnection, as well as those occurring on the

evaluation board, can cause these problems.

A simple (and common) example of such a problem is triple

travel due to mismatch at both the source and the evaluation

board. Here the signal from the source reaches the evaluation

board and mismatch causes a reflection. When that reflection

reaches the source mismatch, it causes a new reflection, which

travels back to the evaluation board, adding to the original

signal incident at the board. The resultant voltage varies with

both cable length and frequency dependence on the relative

phase of the initial and reflected signals. Placing the 3 dB pad at

the input of the board improves the match at the board and thus

reduces the sensitivity to mismatches at the source. When such

precautions are taken, measurements are less sensitive to cable

length and other fixture issues. In an actual application when

the distance between AD8361 and source is short and well

defined, this 3 dB attenuator is not needed.

CHARACTERIZATION SETUPS

Equipment

The primary characterization setup is shown in Figure 72. The

signal source used was a Rohde & Schwarz SMIQ03B, version

3.90HX. The modulated waveforms used for IS95 reverse link,

IS95 nine active channels forward (forward link 18 setting),

and W-CDMA 4-channel and 15-channel were generated using

the default settings coding and filtering. Signal levels were

calibrated into a 50 Ω impedance.

Analysis

The conversion gain and output reference are derived using the

coefficients of a linear regression performed on data collected

in its central operating range (35 mV rms to 250 mV rms). This

range was chosen to avoid areas of operation where offset

distorts the linear response. Error is stated in two forms error

from linear response to CW waveform and output delta from

2°C performance.

The error from linear response to CW waveform is the

difference in output from the ideal output defined by the

conversion gain and output reference. This is a measure of both

the linearity of the device response to both CW and modulated

waveforms. The error in dB uses the conversion gain multiplied

by the input as its reference. Error from linear response to CW

waveform is not a measure of absolute accuracy, since it is

calculated using the gain and output reference of each device.

However, it does show the linearity and effect of modulation on

the device response. Error from 25° C performance uses the

performance of a given device and waveform type as the

reference; it is predominantly a measure of output variation

with temperature.

AD8361

VPOS

IREF

RFIN

PWDN

SREF

VRMS

FLTR

COMM

0.1

µF

Ω

RFIN

0.1

µF

100pF

IREF

PWDN

VPOS

SREF

VRMS

Figure 71. Characterization Board

AD8361

CHARACTERIZATION

BOARD

RFIN

PRUP

+VS SREF IREF

VRMS

DC OUTPUT

RF SIGNAL

SMIQ038B

RF SOURCE

IEEE BUS

PC CONTROLLER

DC MATRIX / DC SUPPLIES / DMM

DC SOURCES

3dB

ATTENUATOR

Figure 72. Characterization Setup

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