Copyright © 2000, Texas Instruments Incorporated

SBWS014

Printed in U.S.A. December, 2000

ADSL ANALOG FRONT-END

FEATURES

q NOISE FLOOR: –144dBm/Hz

q MULTIRATE COMPATIBLE

q VCXO CIRCUITRY AND DAC

AFE1302

DESCRIPTION

Burr-Brown’s Analog Front-End from Texas Instru-

ments reduces the size and cost of an ADSL-compliant

system by providing the active analog circuitry needed

to connect an ADSL Digital Signal Processor (DSP) to

an external line driver, receiver, TX/RX filters, hy-

brid, transformer, and POTS filter. The AFE1302 is

designed for downstream data rates of 4Mbps and

higher, and operation at a clock rate of 35.328MHz,

with an output word rate of up to 8.832MWords/s.

Functionally, this unit consists of a transmit (TX) chan-

nel, a receive (RX) channel, a VCXO (Voltage Con-

trolled Crystal Oscillator) control Digital-to-Analog

Converter (DAC), and VCXO active circuitry. The TX

section converts, filters, and buffers outgoing Discrete

Multi Tone (DMT) data from the ADSL DSP.

The receive section amplifies, filters, and digitizes the

DMT data received on the twisted pair line.

This IC operates on a single 5V supply. The digital

circuitry in the unit can be connected to a supply voltage

ranging from 3.3V to 5V. The chip uses only 570mW.

The AFE1302 is designed to be used with external

amplifiers and filters for noise reduction and dynamic-

range improvement.

The RX channel consists of a low-noise PGA, a switched

capacitor low-pass filter, and fourth-order delta-sigma

Analog-to-Digital Converter (ADC). The delta-sigma

modulator operating at a 32X oversampling ratio pro-

duces a 16-bit output at word rates up to 8832kHz.

The TX channel consists of a fourth-order delta-sigma

DAC, switched-capacitor low-pass filter, program-

mable attenuator, and buffer. The buffer drives off-

chip into a low-noise line driver configured as a 3-pole

active filter to produce an overall low-noise high-drive

TX output signal on a twisted pair line.

q 8.8M TO 1.1MWords/s WORD RATE

q FIVE GENERAL-PURPOSE OUTPUTS

q 570mW POWER DISSIPATION

q TQFP-48 PACKAGE

16-Bit

DAC

16-Bit

ADC

VCXO

DAC

Atten

PGA

Interpolation

Filter

Decimation

Filter

Analog

Loop Back

General Purpose

Digital Output

VCXO

Active Ckts

Buffer

LP

Filter

LP

Filter

Digital

Interface

From DSP

TX Output

RX Input

5

AFE1302

Digital

Loopback

Patents Pending

www.ti.com

AFE1

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