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ADL5390ACPZ-WP

RF/IF Vector Multiplier

Analog Devices 

ADL5390

GENERALIZED MODULATOR

The ADL5390 can be configured as a traditional IQ quadrature

modulator or as a linear vector modulator by applying signals

that are in quadrature to the RF/IF input channels. Since the

quadrature generation is performed externally, its accuracy and

bandwidth are determined by the user. The user-defined band-

width is attractive for multioctave or lower IF applications

where on-chip, high accuracy quadrature generation is tradi-

tionally difficult or impractical. The gain control pins (IBBP/M

and QBBP/M) become the in-phase (I) and quadrature (Q) base-

band inputs for the quadrature modulator and the gain/phase

control for the vector modulator. The wide modulation band-

widths of the gain control interface allow for high fidelity base-

band signals to be generated for the quadrature modulator and

for high speed gain and phase adjustments to be generated for

the vector modulator.

RF/IF signals can be introduce to the ADL5390 in quadrature

by using a two-way 90o power splitter such as the Mini-Circuits

QCN-12. Each output of an ideal 90o power splitter is 3 dB

smaller than the input and has a 90o phase difference from the

other output. In reality, the 90o power splitter will have its own

insertion loss, which can be different for each output, causing a

magnitude imbalance. Furthermore, quadrature output will not

be maintained over a large frequency range, introducing a phase

imbalance. The type of 90o power splitter that should be used

for a particular application will be determined by the frequency,

bandwidth, and accuracy needed. In some applications minor

magnitude and phase imbalances can be adjusted for in the

I/Q gain control inputs.

VECTOR MODULATOR

Vq

+0.5

MAX GAIN = 5dB

A

|A|

θ

–0.5

+0.5 Vi

MIN GAIN < –30dB

–0.5

Figure 34. Vector Gain Representation

The ADL5390 can be used as a vector modulator by driving the

RF I and Q inputs single-ended through a 90o power splitter. By

controlling the relative amounts of I and Q components that are

summed, continuous magnitude and phase control of the gain

is possible. Consider the vector gain representation of the

ADL5390 expressed in polar form in Figure 34. The attenuation

factors for the RF I and Q signal components are represented on

the x-axis and y-axis, respectively, by the baseband gain control

inputs VIBB and VQBB. The resultant of their vector sum represents

the vector gain, which can also be expressed as a magnitude and

phase. By applying different combinations of baseband inputs,

any vector gain within the unit circle can be programmed. The

magnitude and phase (with respect to 90o) accuracy of the 90o

power splitter will directly affect this representation and could

be seen as an offset and skew of the circle.

A change in sign of VIBB or VQBB can be viewed as a change in

sign of the gain or as a 180° phase change. The outermost circle

represents the maximum gain magnitude. The circle origin

implies, in theory, a gain of 0. In practice, circuit mismatches

and unavoidable signal feedthrough limit the minimum gain to

approximately −30 dB. The phase angle between the resultant

gain vector and the positive x-axis is defined as the phase shift.

Note that there is a nominal, systematic insertion phase through

the ADL5390 to which the phase shift is added. In the following

discussions, the systematic insertion phase is normalized to 0°.

The correspondence between the desired gain and phase and

the Cartesian inputs VIBB and VQBB is given by simple trigono-

metric identities

[ ( ) ] ( ) Gain = VIBB /VO 2 + VQBB /VO 2

( ) Phase = arctan VQBB /VIBB

where:

VO is the baseband scaling constant (285 mV).

VIBB and VQBB are the differential I and Q baseband voltages

centered around 500 mV, respectively (VIBB = VIBBP − VIBBM;

VQBB = VQBBP − VQBBM).

Note that when evaluating the arctangent function, the proper

phase quadrant must be selected. For example, if the principal

value of the arctangent (known as arctangent(x)) is used, quad-

rants 2 and 3 would be interpreted mistakenly as quadrants 4

and 1, respectively. In general, both VIBB and VQBB are needed in

concert to modulate the gain and the phase.

Pure amplitude modulation is represented by radial movement

of the gain vector tip at a fixed angle, while pure phase modula-

tion is represented by rotation of the tip around the circle at a

fixed radius. Unlike traditional I-Q modulators, the ADL5390 is

designed to have a linear RF signal path from input to output.

Traditional I-Q modulators provide a limited LO carrier path

through which any amplitude information is removed.

VECTOR MODULATOR EXAMPLE—CDMA2000

The ADL5390 can be used as a vector modulator by driving the

RF I and Q inputs (INPI and INPQ) single-ended through a 90o

power splitter and controlling the magnitude and phase using

the gain control inputs. To demonstrate operation as a vector

modulator, an 880 MHz single-carrier CDMA2000 test model

signal (forward pilot, sync, paging, and six traffic as per

Rev. 0 | Page 15 of 24

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