ADL5371(RevA) Ver la hoja de datos (PDF) - Analog Devices

Número de pieza

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Fabricante

ADL5371
(Rev.:RevA)

500 MHz to 1500 MHz Quadrature Modulator

Analog Devices 

ADL5371

THEORY OF OPERATION

CIRCUIT DESCRIPTION

Overview

The ADL5371 can be divided into five circuit blocks: the LO

interface, the baseband voltage-to-current (V-to-I) converter,

the mixers, the differential-to-single-ended (D-to-S) converter,

and the bias circuit. A detailed block diagram of the device is

shown in Figure 22.

LOIP

LOIN

PHASE

SPLITTER

IBBP

IBBN

QBBP

QBBN

Σ

OUT

Figure 22. Block Diagram

The LO interface generates two LO signals in quadrature. These

signals are used to drive the mixers. The I/Q baseband input

signals are converted to currents by the V-to-I stages, which

then drive the two mixers. The outputs of these mixers combine

to feed the output balun, which provides a single-ended output

interface. The bias cell generates a reference current for the

V-to-I stage.

LO Interface

The LO interface consists of a polyphase quadrature splitter

followed by a limiting amplifier. The LO input impedance is set

by the polyphase. The LO can be driven either single-ended or

differentially. When driven single-ended, the LOIN pin should

be ac-grounded via a capacitor. Each quadrature LO signal then

passes through a limiting amplifier that provides the mixer with

a limited drive signal.

Data Sheet

V-to-I Converter

The differential baseband inputs (QBBP, QBBN, IBBN, and

IBBP) consist of the bases of PNP transistors, which present a

high impedance. The voltages applied to these pins drive the

V-to-I stage that converts baseband voltages into currents. The

differential output currents of the V-to-I stages feed each of

their respective Gilbert-cell mixers. The dc common-mode

voltage at the baseband inputs sets the currents in the two mixer

cores. Varying the baseband common-mode voltage varies the

current in the mixer and affects overall modulator performance.

The recommended dc voltage for the baseband common-mode

voltage is 500 mV dc.

Mixers

The ADL5371 has two double-balanced mixers: one for the

in-phase channel (I channel) and one for the quadrature

channel (Q channel). Both mixers are based on the Gilbert-cell

design of four cross-connected transistors. The output currents

from the two mixers sum together into an on-chip balun, which

converts the differential signal to single-ended.

D-to-S Stage

The output D-to-S stage consists of an on-chip balun that

converts the differential signal to a single-ended signal. The

balun presents high impedance to the output (VOUT).

Therefore, a matching network may be needed at the output for

optimal power transfer.

Bias Circuit

An on-chip band gap reference circuit is used to generate a

proportional-to-absolute temperature (PTAT) reference current

for the V-to-I stage.

Rev. A | Page 10 of 20

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