STLC60134S 데이터 시트보기 (PDF) - STMicroelectronics
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STLC60134S Datasheet PDF : 22 Pages
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STLC60134S
the ATU-C/ATU-R receivers and transmitters. Ex-
ternal low noise driver and input stage used with
STLC60134S guarantee low noise performances.
The STLC60134S chip can be used at ATU-C
and ATU-R ends (behaviour set by LTNT pin).
The selection consists mainly of a filter inter-
change between the RX and TX path. The filters
(with a programmable cutoff frequency) use auto-
matic Continuous Time Tuning to avoid time vary-
ing phase characteristic which can be of dramatic
consequence for DMT modem. It requires few ex-
ternal components, uses a 3.3V supply (a sepa-
rate 3.0V supply of the digital part is possible)
and is packaged in a 64-pin TQFP in order to re-
duce PCB area.
The Receiver (RX) part
The DMT signal coming from the line to the
STLC60134S is first filtered by the two following
external filters:
POTS HP filter:
Channel filter:
Attenuation of speech and POTS
signalling
Attenuation of echo signal to
improve RX dynamic
An analog multiplexer allows the selection be-
tween two input ports which can be used to select
an attenuated(0, 10dB for ex.) version of the sig-
nal in case of short loop or large echo. The sig-
nal is amplified by a low noise gain stage (0-
31dB) then low-pass filtered to avoid anti-aliasing
and to ease further digital processing by remov-
ing unwanted high frequency out-of-band noise.
A 12-bit A/D converter samples the data at
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 proces-
sor through the digital interface are transformed
by D/A converter into a analog signal.
This signal is then filtered to decrease DMT side-
lobes level and meet the ANSI transmitter spec-
tral 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 aux-
iliary 8 bits DAC for timing recovery.
The XTAL driver is able to operate at 35.328MHz
and provides an amplitude regulation mechanism
to avoid temperature / supply / technology de-
pendent frequency pulling.
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 be-
tween DAC input and VCXO output can be intro-
duced (via the CTLIN interface) and programmed
with the help of an external capacitor (on VCOC
pin).
See chapter ’VCXO’ for the external circuit re-
lated to the VCXO.
The Digital Interface part
The digital part of the STLC60134S can be di-
vided in 3 sections:
The data interface converts the multiplexed
data from/to the DMT signal processor into
valid representation for the TX DAC and RX
ADC. It performs also the error correction
mechanism needed at the (redundant) ADC
output.
The control interface allows the board proces-
sor to configure the STLC60134S paths
(RX/TX gains, filter band, ...) or settings (OSR,
vcodac enable, digital / analog loopback,...).
The test interface to enable digital (Full Scan,
nandtree, loop backs, functional,...) or analog
(TIN, TOUT assignation) tests to be per-
formed.
DMT Signal
A DMT signal is basically the sum of N inde-
pendently QAM modulated signals, each carried
over a distinct carrier. The frequency separation
of each carrier is 4.3125kHz with a total number
of 256 carriers (ANSI). For N large, the signal can
be modelled by a gaussian process with a certain
amplitude probability density function. Since the
maximum amplitude is expected to arise very
rarely, we decide to clip the signal and to trade-
off the resulting SNR loss against AD/DA dy-
namic. A clipping factor (Vpeak/Vrms = ”crest fac-
tor”) of 5 will be used resulting in a maximum
SNR of 75dB.
ADSL DMT signals are nominally sent at -40dBm/Hz
±3dB (-3.65dBm/carrier) with a maximal power of
100mW for down link transmitter and 15.7mW for
uplink transmitter.
DMT symbols are transmitted without ’window-
ing’ causing sin (x)/x like sidelobes. For spectral
response shaping, the 1st sidelobe level is as-
sumed to be 13dB under the carrier level with
an attenuation of -20dB/dec.
The minimum SNR + D neede d for DMT carrier
demodulation is about (3 ⋅ N + 20) dB with a
minimum of 38dB were N is the constellation size
of a carrier (in bits).
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