3/7

ST20190

Figure 3. Block Diagram of ST20184

5.2 ST20196

5.2.1 Discrete Multi Tone (DMT) Modulation and Demodulation

The ST20196 includes a digital Quadrature Amplitude Modulation (QAM) mapper/demapper which allows

coding of up to 15 bits per tone. The device incorporates the necessary Inverse- and Fast Fourier Trans-

form (IFFT, FFT), an innovative unique Per Tone Equalizer (PTEQ), echo cancelling (EC), Trellis coding

and decoding plus timing units and a fully digital clock recovery scheme (TDI). These last blocks feature

efficient synchronization algorithms to improve the efficiency of the recovery of data. The ST20196 per-

formances rely on embedded programmable cores.

In ADSL2 mode the modem supports diagnostics modes, enhanced power management modes to reduce

the CO power (L2), 1 bit constellation, relocatable and modulated pilot.

5.2.2 Framing Functions

The ST20196 incorporates framing functions for the generic and ATM Transmission Convergence (TC)

layers. The new TC layer architecture is fully under the control of an embedded controller. This provides

the flexibility to adapt to different framing variants via firmware. The TC consists of data scrambling and

Reed-Solomon error correction with and without inter-leaving. It also includes the rate converter function-

ality as defined in G.dmt Annex C. Several framing variants are implemented (such as interleaved and

non-interleaved modes, full and reduced overhead) to ensure compliance with ANSI T1.413 Issue 2 and

ITU G.992.1 (G.dmt), G.992.2 (G.Lite), G.992.3 and G.992.4.

RX LPF

ADC

TX LPF

DAC

D

I

G

I

T

A

L

TXLD

TXP

TXN

Dying Gasp

Tuning Circuit

I/V Reference

VCXO

(optional)

CTRL/TST

Interface

2.5V Regulator

+

POR

LNA1ab

RX HPF

LNA2

RXP1

RXN1

LNA1c

RXP2

RXN2

RXP3

RXN3

Bypass

Bypass

Loopback

5V area

Digital

Hybrid

switches