ST70134 datasheet(2/22 Pages) STMICROELECTRONICS

2 / 22 page

ST70134A

2/22

Figure 1 : Block Diagram

The Receiver (RX) Part

The DMT signal coming from the line to the

ST70134 is first filtered by two external filters,

Pots HP and channel filters.

analog

multiplexer

allows

the

selection

between two input ports which can be used to

select an attenuated (0, 10dB for ex.) version of

the signal in case of short loop or large echo.

The signal is amplified by a low noise gain stage

(0-31dB) then low-pass filtered to avoid aliasing

and to ease further digital processing by removing

unwanted high frequency out-of-band noise.A

13-bit

A/D

converter

samples

the

data

8.832MS/s (or 4.416MS/s in alternative mode),

transforms the signal into a digital representation

and sends it to the DMT signal processor via the

digital interface.

The Transmitter (TX) part

The 12-bit data words at 8.832MS/s (or 4.416MS/

s) coming from the DMT signal processor through

the digital interface are transformed by D/A con-

verter into a analog signal.

This signal is then filtered to decrease DMT side-

lobes level and meet the ANSI transmitter spectral

response but also to reduce the out-of-band noise

(which can be echoed to the RX path) to an

acceptable level. The pre-driver buffers the signal

for the external line driver and in case of short

loop provide attenuation (-15...0dB).

The VCXO Part

The VCXO is divided in a XTAL driver and a auxil-

iary 8 bits DAC for timing recovery.The XTAL

driver is able to operate at 35.328MHz.

The DAC which is driven by the CTRLIN pin pro-

vides a current output with 8-bit resolution and

can be used to tune the XTAL frequency with the

help of external components.

A time constant between DAC input and VCXO

output can be introduced (via the CTLIN interface)

and programmed with the help of an external

capacitor (on VCOC pin).See chapter ’VCXO’ for

the external circuit related to the VCXO.

The Digital Interface Part

The digital part of the ST70134 can be divided in 2

sections:

– The data interface converts the multiplexed data

from/to the DMT signal processor into valid

representation for the TX DAC and RX ADC.

– The control interface allows the board processor

to configure the STL70134 paths (RX/TX gains,

filter band, ...) or settings (OSR, vcodac enable,

digital / analog loopback,...).

R-MOS-C

TUNING

I/V-REF

XTAL-DRIVER

VCXO DAC

G = -15...0dB

step = 1dB

AGCtx

TXP

TXN

1.1MHz

HC2

1.1MHz

HC1

138kHz

SC2

DIGITAL

DAC

AGCrx

G = 0...31dB

step = 1dB

RXP(0:1)

RXN(0:1)

ADC

13 Bits

12 Bits

Rx (0:3)

Tx (0:3)

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