ADL5373ACPZ-WP 데이터 시트보기 (PDF) - Analog Devices

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ADL5373ACPZ-WP

2300 MHz to 3000 MHz Quadrature Modulator

Analog Devices 

Data Sheet

THEORY OF OPERATION

CIRCUIT DESCRIPTION

Overview

The ADL5373 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) stage, and

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

in Figure 24.

LOIP

LOIN

PHASE

SPLITTER

IBBP

IBBN

QBBP

QBBN

Σ

VOUT

Figure 24. Block Diagram

The LO interface generates two LO signals in quadrature. These

signals are used to drive the mixers. The I and 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.

The bias cell generates reference currents 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. For optimal performance, the LO should be

driven differentially. Each quadrature LO signal then passes

through a limiting amplifier that provides the mixer with a

limited drive signal.

ADL5373

V-to-I Converter

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

IBBP) consist of the bases of the 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 influences 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 ADL5373 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 a load. The signal developed across

this load is used to drive the D-to-S stage.

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. B | Page 11 of 20

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