STLC1510 datasheet(20/40 Pages) STMICROELECTRONICS

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STLC1510

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5.9 Digital Front End (DFE)

The Digital Front End (DFE) block contains dedicated

hardware to map signals between the analog inter-

face (AFE) and the BPU.

The DFE block has the following features:

It performs part of the sampling rate conversion

between the AFE sampling rate and the 2x

symbol rate of the BPU.

It provides the necessary digital hardware to

implement an analog-based AGC.

It provides the necessary buffering to provide

DMT symbol alignment within the BPU.

It provides the facilities to allow timing recovery

in CPE mode. This consists of a digital phase

interpolator and a digital

Σ∆ D/A convertor

Two loopback modes are provided in this block.

Various bypass modes are provided to allow

observation and isolation of any block in the

DFE for test purposes.

Interface to the LAMBA Bus.

5.9.1 Application Description

Figure 7. shows the application of the various DFE

components when used in a CO (network) and CPE

(remote) applications.

5.9.2 Interface Description

The registers accessible by the EPM are:

Decimator oversampling ratio

Decimator order.

Various loopback and bypass modes.

Number of bits transferred to the Aloha ASIC

DAC.

AFE control registers.

ADC clip counter.

RSM parameters such as time constant, peak

detector thresholds, peak detector modes,

integrator initialization, and detector outputs.

IIR coefficients.

Predictor IIR filter coefficients.

Frame synchronization buffer length

Timing recovery (crystal) control word.

Timing recovery

Σ∆ dither level selection.

CO/CPE mode selection.

Phase interpolator parameters such as alpha,

frequency error and frequency error gain.

CO peak detector parameters such as set-up

and hold delays, threshold, and slew rate.

Figure 7. DFE Application Diagram

II R

I n terpola tin g

CS D F I R

II R

BP U

An a lo g

Do m a i n

In te rp

CS D

CI C

Filter

FIFO

DA C

AD C

DA C

AD C

S TLC 15 1 0 (C O)

S TLC 15 20 (C P E )

DF E

CIC

F ilter

CIC

F ilter

FI R

CIC

F ilter

RS M

Σ∆

optional

PI F

Dly

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