ST70134 datasheet(3/22 Pages) STMICROELECTRONICS

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ST70134A

3/22

DMT Signal (Done by the DMT companion

chip)

A DMT signal is basically the sum of N indepen-

dently QAM modulated signals, each carried over

a distinct carrier. The frequency separation of

each carrier is 4.3125kHz with a total number of

256 carriers (ANSI). For N large, the signal can be

modelled by a gaussian process with a certain

amplitude probability density function. Since the

maximum amplitude is expected to arise very

rarely, we decide to clip the signal and to trade-off

the resulting SNR loss against AD/DA dynamic. A

clipping factor (Vpeak/Vrms = "crest factor") of 5.3

will be used resulting in a maximum SNR of 75dB.

ADSL DMT signals are nominally sent at an aver-

age of -38dBmHz (-1.65dBm/carrier) with a maxi-

mal

power

15.7mW

for

the

transmitter

(upstream for ADSL over Pots, DMT carriers are

from 7 to 31, for ADSL over ISDN DMT carriers

are from 31 to 64).

Maximum / Minimum Signal Levels

The following table gives the transmitted and

received signal levels for CPE (ATU-R) and, for

reference, at ATU-C. All the levels are referred to

the line voltages (i.e. after hybrid and transform-

ers in TX direction, before hybrid and transformer

in RX direction).

Note that signal amplitudes shown below are for

illustration purpose and depending on the transmit

power and line impedance signal amplitudes can

differ from these values.

The reference line impedance for all power calcu-

lations is 100

Ω.

Package

The ST70134 is packaged in a 64-pin TQFP pack-

age (body size 10x10mm, pitch 0.5mm).

* Power cut back software co facility.

Table 1 : Target Signal Levels (on the line)

Parameter

ATU - R

ATU - C (for reference)

Max level

3.95 Vpdif *

6.8 Vpdif

1.66 mVpdif

15.8 Vpdif *

Max RMS level

791 mVrms

671 mVrms

168 mVrms

3.16 Vrms

Min level

42 mVpdif

839 mVpdif

54 mVpdif

3.95 Vpdif

Min RMS level

8 mVrms

168 mVrms

11 mVrms

791 mVrms

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