ST70235A STMicroelectronics, ST70235A Datasheet - Page 11

• Manufacturer Part Number: ST70235A
• Description: Transceiver 144-Pin TQFP
• Manufacturer: STMicroelectronics

Specifications of ST70235A

• Package: 144TQFP
• Power Supply Type: Analog
• Typical Operating Supply Voltage: 1.8|3.3 V
• Minimum Operating Supply Voltage: 1.62|3 V
• Maximum Operating Supply Voltage: 1.98|3.6 V
• Case: QFP

The FFT module is a slave DSP engine controlled
by the firmware running on an external controller.
It works off line and communicates with other
blocks through buffers controlled by the "Data
Symbol Timing Unit". The DSP executes a
program stored in a RAM area, which constitutes
a flexible element that allows for future system
enhancements.
DPLL
The Digital PLL module receives a metric for the
phase error of the pilot tone. In general, the clock
frequencies at the ends (transmitter and receiver)
do not match exactly. The phase error is filtered
and integrated by a low pass filter, yielding an
estimation of the frequency offset. Various
processes can use this estimate to deal with the
frequency mismatch.
In particular, small accumulated phase error can
be compensated in the frequency domain by a
rotation of the received code constellation (Rotor).
Larger errors are compensated in the time domain
by inserting or deleting clock cycles in the sample
input sequence.
Eventually that leads to achieve less than 2ppm
between the two ends.
Mapper/Demapper, Monitor, Trellis Coding,
FEQ Update
The Demapper converts the constellation points
computed by the FFT to a block of bits. This
means to identify a point in a 2D QAM
constellation plane. The Demapper supports
Trellis coded demodulation and provides a Viterbi
maximum likelihood estimator. When the Trellis is
active, the Demapper receives an indication for
the most likely constellation subset to be used.
In the transmit direction, the mapper receives a bit
stream from the Trellis encoder and modulates
the bit stream on a set of carriers (up to 256). It
generates coordinates for 2n QAM constellation,
where n < 15 for all carriers.
The Mapper performs the inverse operation,
mapping a block of bits into one constellation
point (in a complex x+jy representation) which is
passed to the IFFT block. The Trellis Encoder
generates
robustness
4-Dimensional Trellis Coded Modulation scheme.
This
computes error parameters for carriers specified
in the Demapper process. Those parameters can
be used for updates of adaptive filters coefficients,
clock phase adjustments, error detection, etc. A
series of values is constantly monitored, such as
feature
redundant
of
can
the
be
transmission,
bits
disabled.The
to
improve
using
Monitor
the
a
signal power, pilot phase deviations, symbol
erasures generation, loss of frame, etc.
Generic TC Layer Functions
These functions relate to byte oriented data
streams. They are completely described in ANSI
T 1.4 13. Additions described in the Issue 2 of this
specification are also supported.
The data received from the demapper may be
split into two paths, one dedicated to an
interleaved data flow the other one for a fast data
flow. No external RAM is needed for the
interleaved path.
The
increase the error correcting capability of block
codes for error bursts.
After deinterleaving (if applicable), the data flow
enters a Reed-Solomon error correcting code
decoder, able to correct a number of bytes
containing bit errors.
The decoder also uses the information of previous
receiving stages that may have detected the error
bytes and have labelled them with an "erasure
indication". Each time the RS decoder detects and
corrects errors in a RS codeword, an RS
correction event is generated.
The occurrence of such events can be signalled to
the management layer.After the RS decoder, the
corrected byte stream is descrambled in the PMD
(Physical Medium Dependent) descramblers. Two
descramblers are used, for interleaved and
non-interleaved data flows. These are defined in
ANSI T1.413. After descrambling, the data flows
enter the Deframer that extracts and processes
bytes to support Physical layer related functions
according to ANSI T1.413. The ADSL frames
indeed contain physical layer-related information
in addition to the data passed to the higher layers.
In particular, the deframer extracts the EOC
(Embedded Operations Channel), the
(ADSL Overhead Control) and the indicators bits
and passes them to the appropriate processing
unit (e.g. the transceiver controller). The deframer
also performs a CRC check (Cyclic Redundancy
Check) on the received frame and generates
events in case of error detection.Event counters
can be read by management processes.
The outputs of the deframer are an interleaved
and a fast data streams. These data streams can
either carry ATM cells or another type of traffic. In
the latter case, the ATM specific TC layer
functional block, described hereafter, is bypassed
and the data stream is directly presented at the
input of the interface module.
interleaving/deinterleaving
is
ST70235A
used
11/28
AOC
to