PRELIMINARY TECHNICAL DATA

Rev. PrF 2/11/03

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3

50–1000 MHz

a

Quadrature Demodulator

Preliminary Technical Data

AD8348

Features

Integrated I/Q demodulator with IF VGA Amplifier

Operating IF Frequency 50–1000 MHz

(3dB IF BW of 500MHz driven from Rs=200ohms)

Demodulation Bandwidth 60MHz

Linear-in-dB AGC Range 45dB

Third Order Intercept

IIP3 +26 dBm @ min gain (FIF=450MHz)

IIP3 -7 dBm @ max gain (FIF=450MHz)

Quadrature Demodulation Accuracy

Phase Accuracy 0.6

Amplitude Balance 0.3 dB

Noise Figure 12.5dB @ max gain (FIF=500MHz)

LO Input -10 dBm

Single Supply 2.7-5.5V

Power down mode

Compact 28-pin TSSOP package

Applications

QAM/QPSK Demodulator

W-CDMA/CDMA/GSM/NADC

Wireless Local Loop

LMDS/MMDS

General Description

The AD8348 is a broadband quadrature demodulator with an

integrated intermediate frequency (IF) variable-gain amplifier

(VGA) and integrated baseband amplifiers. It is suitable for

use in communications receivers, performing quadrature

demodulation from IF directly to baseband frequencies. The

baseband amplifiers have been designed to directly interface

with dual channel A-to-D converters such as the AD9201,

AD9283, and AD9218 for digitizing and post-processing.

The IF input signal is fed into two Gilbert-cell mixers through

an X-AMP VGA. The IF VGA provides 45dB of gain

control. A precision gain-control circuit sets a linear-in-dB

gain characteristic for the VGA and provides temperature

compensation. The LO quadrature phase splitter employs a

divide-by-two frequency divider to achieve high quadrature

accuracy and amplitude balance over the entire operating fre-

quency range.

Optionally, the IF VGA can be disabled and bypassed. In this

mode, the IF signal is applied directly to the quadrature mixer

inputs via pins MXIP and MXIN.

Functional Block Diagram

Separate I & Q-channel baseband amplifiers follow the

baseband outputs of the mixers. The DC common-mode

voltage level at the baseband outputs is set by the voltage

applied to the VCMO pin. Typically VCMO is connected to

the internal VREF voltage but it can also be connected to an

external voltage. This flexibility allows the user to maximize

the input dynamic range to the A-to-D converter. Connecting

a bypass capacitor at each offset compensation input (IOFS &

QOFS) nulls DC offsets produced in the mixer. Offset

compensation can be overridden by applying an external

voltage at the offset compensation inputs.

The mixers’ outputs are brought off-chip for optional filtering

before final amplification. Inserting a channel selection filter

before each baseband amplifier increases the baseband

amplifiers’ signal handling range by reducing the amplitude of

high-level, out-of-channel interferers before the baseband

signal is fed into the baseband amplifiers. The single-ended

mixer output is amplified and converted to a differential signal

for driving ADCs.