REV. 0

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

a

AD6432

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 617/329-4700

World Wide Web Site: http://www.analog.com

Fax: 617/326-8703

© Analog Devices, Inc., 1997

GSM 3 V Transceiver IF Subsystem

FUNCTIONAL BLOCK DIAGRAM

SAW

BP

OP AMP

AD6432

PA

RF

SYNTH

IF

SYNTH

PLO

FEATURES

Fully Compliant with Standard and Enhanced GSM

Specification

DC-350 MHz RF Bandwidths

80 dB Gain Control Range

I/Q Modulation and Demodulation

Onboard Phase Locked Tunable Oscillator

On-Chip Noise Roofing IF Filters

Ultralow Power Design

2.7 V–3.6 V Operating Voltage

User-Selectable Power-Down Modes

Small 44-Lead TQFP Package

Interfaces Directly with AD20msp410 and AD20msp415

GSM Baseband Chipsets

APPLICATIONS

I/Q Modulated Digital Wireless Systems

GSM Mobile Radios

GSM PCMCIA Cards

GENERAL DESCRIPTION

The AD6432 IF IC provides the complete transmit and receive

IF signal processing, including I/Q modulation and demodula-

tion, necessary to implement a digital wireless transceiver such

as a GSM handset. The AD6432 may also be used for other

wireless TDMA standards using I/Q modulation.

The AD6432’s receive signal path is based on the proven archi-

tecture of the AD607 and the AD6459. It consists of a mixer,

gain-controlled amplifiers, integrated roofing filter and I/Q

demodulators based on a PLL. The low noise, high-intercept

variable-gain mixer is a doubly-balanced Gilbert-cell type. It has

a nominal –13 dBm input-referred 1 dB compression point and

a 0 dBm input-referred third-order intercept.

The gain-control input accepts an external control voltage input

from an external AGC detector or a DAC. It provides an 80 dB

gain range with 27.5 mV/dB gain scaling, where the mixer and

the IF gains vary together.

The I and Q demodulators provide inphase and quadrature

baseband outputs to interface with Analog Devices’ AD7015

and AD6421 (GSM, DCS1800, PCS1900) baseband convert-

ers. An onboard quadrature VCO, externally phase-locked to

the IF signal, drives the I and Q demodulators. The quadrature

phase-locked oscillator (QPLO) requires no external compo-

nents for frequency control or quadrature generation, and de-

modulates signals at standard GSM system IFs of 13 MHz, or

26 MHz with a reference input frequency of 13 MHz; or, in

general, 1X or 2X the reference frequency. Maximum reference

frequency is 25 MHz.

This reference signal is normally provided by an external

VCTCXO under the control of the radio’s digital signal

processor. The transmit path consists of an I/Q modulator

and buffer amplifier, suitable for carrier frequencies up to

300 MHz and provides an output power of –17.5 dBm in

a 50

Ω system. The quadrature LO signals driving the

I and Q modulator are generated internally by dividing by

two the frequency of the signal presented at the differential

LO port of the AD6432. In both the transmit and receive

paths, onboard filters provide 30 dB of stopband attenuation.

The AD6432 comes in a 44-lead plastic thin quad flatpack

(TQFP) surface mount package.