stlc3040 STMicroelectronics, stlc3040 Datasheet - Page 4

• Manufacturer Part Number: stlc3040
• Description: Subscriber Line Interface Codec Filter, Cofislic
• Manufacturer: STMicroelectronics

STLC3040
4 FUNCTIONAL DESCRIPTION
The STLC3040 is implemented by a combination
of analog and digital circuits, merging the best
available analog and digital processing perform-
ances of the BiCMOS technology. In particular
two main blocks of the STLC3040 can be identi-
fied: an analog front end interfacing the HV
(L3000N, L3000S, STLC3170) and a programma-
ble DSP. (See fig. 3)
4.1 - Signal processing.
The line-current signal received in pin IT from the
HV (L3000N, L3000S, STLC3170) is mirrored out
of pin ACDC. On its way, its value is sensed to
determine Off-Hook signalling.
conversation this istantaneous sensing is used for
fast Hook signalling such as numbering. Then
line-current AC and DC parts are splitted by RDC
and CAC. The signal is processed to realize AC
and DC impedance synthesis. Indeed IT pin car-
ries the AC current due to voice signals present at
line terminals and the DC current related to the
specific V-I operating point.
During Stand-By mode signal is created by the
DC current after AC part has been removed. This
filtered Hook produces robust signalling in Stand-
by mode or pause-period during reduced-power
Ring mode.
As far as the DC characteristic is concerned, two
Figure 3: Block Diagram.
4/49
FSC
DCL
DU
DD
Rx
Tx
GCI
INT.
LB1
LB1
Comp.
exp.
A/u
A/u
DIGITAL SIGNAL PROCESSOR
GR
GX
D95TL205D
Canc.
Echo
While in active
+
B
Ilim
R
X
RDC
IT
+
+
RDC
KD
Z
DSD
DC Char
different conditions are present and depend on
loop resistance.
a) Resistive Feed Region: the SLIC kit operates
b) Constant current region: when IL reaches the
Concerning AC Processing the AC current-signal
is converted to voltage on the reference resistor
RAC (1620 ).
Line impedance (real or complex) synthesis is
carried out thanks to programmable filters. All the
filters are integrated in the digital side of COFIS-
LIC except the so called KA filter that is in the
Analog Front End.
KD and Z (in digital side) filters allow to match the
line impedance if properly programmed. Further-
more KA ensures stability to impedance synthesis
loop.
In the Receive direction (Rx), the Analog Front
End (AFE) receives a 1-bit modulated composite
signal, which represents part of the voltage to be
forced into the line. It performs DAC and filtering
ACDC
CAC
as a voltage source with a series resistance
equal to (2Rp+n
programmed from 1 to 8 via CR8 register. Vari-
ous values of voltage drops are possible as
shown in Fig. 4.
programmed limiting current value (from 0 to
69.3mA; 1.1mA step via CR6 register), the Kit
operates as a proper constant current source.
(see Fig. 4).
DEC
CAC
LB2
LB3
ANALOG FRONT END
2
Curr. buff.
LB3
50 ), where n can be
ASD
RING
TEST
TTX
Filter
Post
RAC
ANTIALIAS
FILTER
Canc.
TTX
KA
+
RAC
VOUT