ST70134 - ST70135A

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Discrete MultiTone Digital Modem (ST70135A)

The DMT

modem has been

developed in

HCMOS6 (0.35

µm) technology. It performs PMD

(Physycal Medium Dependant) sub-layer and TC

(Transmission Convergence) sub-layer functions.

In other words we can split the chip into two

separate blocks: the first one which carries out

modem functions (PMD sub layer) and a second

one in charge of ATM framing. The chip is

controlled and programmed by an external

processor and is seen as a memory mapped

device.

MODEM Functions

The modem part of the chip includes all the

necessary blocks

needed for digitally DMT

mapping and demapping. A 14-bit code for every

carrier allows constellations with up to 16383

points. Internally, digital filters carry out Time

Equalization to reduce the effects of the inter

symbol interference. That is followed by Fast

Fourier Transform (in transmit direction an Inverse

FFT is performed) in order to change from time

domain to

frequency domain. Afterwards a

Frequency Equalization cuts down carrier by

carrier the channel distortion, signal’s amplitude

attenuation and phase rotation. By efficient

algorithms,

this

block

drives,

through

the

ST70134’s integrated VCXO controller, the NT

crystal oscillator which comes up in an excellent

synchronisation (less than 2ppm) with ATU-C.

FRAMING Functions

ST70135A performs framing functions for generic

and ATM TC sub layers.

ATM TC sub layer performs cell level functions:

delineation,

idle

cells

or

unassigned

cells

insertion/extraction, payload scrambling, Header

Error Correction (HEC) check and data frame

generation.

ST70135A DMT modem main features:

– Time-domain equalisation

– Rotor and frequency-domain equalisation

– Decimation, interpolation

– FFT and IFFT

– Mapping/demapping over 256 carriers

– Trellis coding and decoding using Viterbi algorithm

– Error and noise monitoring on individual tones

– Reed-Solomon encoding and decoding

– (De) framing and (de) interleaving

– Cell HEC generation/verification

– Payload (de) scrambling

– ATM cell insertion/extraction

– Idle &/or Unassigned cell insertion/filtering

– VPI/VCI filtering

– UTOPIA interface (Level 1 or 2)

– Microcontroller interface with 16-bit multiplexed

address/data bus and big/little endian format

supported

– JTAG test port

– Single 3.3V supply, 1.0W

– PQFP144 (28 x 28mm body, 0.65mm pitch)

Figure 3 : DMT Modem block diagram

FFT

Rx

DSP FE

DEMAPPER

VITERBI

CELL

BASED

FUNCT.

DE-

FRAMER

Rx

INTERF.

INTERLEAVED

FAST

SIGNAL MONITORING

& FEQ UPDATE & DPLL

ADSL

AFE

PMD SUBLAYER

TC SUBLAYER

ATM (UTOPIA)

IFFT

Tx

DSP FE

MAPPER

VITERBI

R/S

CODER

CELL

BASED

FUNCT.

FRAMER

Tx

INTERF.

FAST

INTERLEAVED

R/S

DECODER