Copyright © 2000, Texas Instruments Incorporated SBWS014 Printed in U.S.A. December, 2000
ADSL ANALOG FRONT-END
FEATURES
a71 NOISE FLOOR: –144dBm/Hz
a71 MULTIRATE COMPATIBLE
a71 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.
a71 8.8M TO 1.1MWords/s WORD RATE
a71 FIVE GENERAL-PURPOSE OUTPUTS
a71 570mW POWER DISSIPATION
a71 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
AF
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