ST70235A datasheet(9/28 Pages) STMICROELECTRONICS

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ST70235A

9/28

= Input, CMOS levels

I-PU

= Input with pull-up resistance, TTL

levels

I-PD

= Input with pull-down resistance, TTL

levels

I-TTL

= Input TTL levels

= Push-pull output

= Push-pull output with high-impedance

state

= Input / Tristate Push-pull output

BS cell = Boundary-Scan cell

= Input cell

= Output cell

= Bidirectional cell

C= Clock

Main Block Description

The following drawings describe the sequence of

functions performed by the chip.

DSP Front-End

The DSP Front-End contains 4 parts in the

receive direction: the Input Selector, the Analog

Front-End Interface, the Decimator and the Time

Equalizer.

The input selector is used internally to enable test

loopbacks inside the chip. The Analog Front-End

lnterface transfers 16-bit words, multiplexed on 4

input/output signals. Word transfer is carried out in

4 clock cycles.

The Decimator receives 16-bit samples at 8.8MHz

(as sent by the Analog Front-End chip: ST70134)

and reduces this rate to 2.2MHz.

The Time Equalizer (TEQ) module is a FIR filter

with programmable coefficients. Its main purpose

reduce

the

effect

Inter-Symbol

Interferences (ISI) by shortening the channel

impulse response.

Both the Decimator and TEQ can be bypassed. In

the

transmit

direction,

the

DSP

Front-End

includes:

sidelobe

filtering,

clipping,

delay

equalization

and

interpolation.

The

sidelobe

filtering and delay equalization are implemented

by IIR Filters, reducing the effect of echo in FDM

systems.

Clipping is a statistical process limiting the

amplitude of the output signal, optimizing the

dynamic range of the AFE. The interpolator

receives data at 2.2MHz and generates samples

at a rate of 8.8MHz.

DMT Modem

This module is a programmable DSP unit. Its

instruction set enables the basic functions of the

DMT algorithm like FFT, IFFT, Scaling, Rotor and

Frequency Equalization (FEQ) in compliance with

ANSI T1.413 specifications.

In the RX path, the 512-point FFT transforms the

time-domain

DMT

symbol

into

frequency

domain representation which can be further

decoded by the subsequent demapping stages.

In other words, the Fast Fourier Transform

process is used to transform from time domain to

frequency domain (receive path). 1024 time

samples are processed. After the first stage time

domain equalization and FFT block an ICI

(InterCarrier Interference) free information stream

turns out.

MISCELLANEOUS

GP_IN

I-PD

General purpose input

GP_OUT

General purpose output

RESETB

Hard reset

TESTSE

none

Enable scan test mode

IDDq

none

Test pin, active high

COMP_ROUT

none

Compensation cell resistor

DISABLE_COMP

I-PD

Disable compensation cell

Mnemonic

Type

BS Type

Number

of Signals

Function

PIN SUMMARY (continued)

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