TS612ID View Datasheet(PDF) - STMicroelectronics
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Description
Manufacturer
TS612ID Datasheet PDF : 10 Pages
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TS612
ADSL CONCEPT
Asymmetric Digital Subscriber Line (ADSL), is a
new modem technology, which converts the exist-
ing twisted-pair telephone lines into access paths
for multimedia and high speed data communica-
tions.
ADSL transmits more than 8 Mbps to a subscriber,
and can reach 1Mbps from the subscriber to the
central office. ADSL can literally transform the ac-
tual public information network by bringing mov-
ies, television, video catalogs, remote CD-ROMs,
LANs, and the Internet into homes.
An ADSL modem is connected to a twisted-pair
telephone line, creating three information chan-
nels: a high speed downstream channel (up to
1.1MHz) depending on the implementation of the
ADSL architecture, a medium speed upstream
channel (up to 130kHz) and a POTS (Plain Old
Telephone Service), split off from the modem by
filters.
THE LINE INTERFACE - ADSL Remote
Terminal (RT):
The Figure1 shows a typical analog line interface
used for ADSL. The upstream and downstream
signals are separated from the telephone line by
using an hybrid circuit and a line transformer. On
this note, the accent will be made on the emission
path.
Figure 1 : Typical ADSL Line Interface
high output
current
digital to emission LP filter
analog (analog)
digital
treatment
analog to
digital
reception
(analog)
upstream
TS612ID
Line Driver
reception
circuits
impedance
matching
HYBRID
CIRCUIT
twisted-pair
telephone
line
downstream
The TS612 is used as a dual line driver for the up-
stream signal.
For the remote terminal it is required to create an
ADSL modem easy to plug in a PC. In such an ap-
plication, the driver should be implemented with a
+12 volts single power supply. This +12V supply is
available on PCI connector of purchase.
The figure 2 shows a single +12V supply circuit
that uses the TS612 as a remote terminal trans-
mitter in differential mode.
Figure 2 : TS612 as a differential line driver with
a +12V single supply
100n
+ +12V
+12V
1k
_
GND
R2
Vi
47k
1/2 R1
Vcc/2
1/2 R1
Vi
10µ 47k 100n
1k GND
R3
+ +12V
100n
_
GND
1µ
12.5
10n
1:2
Vo
25Ω
Hybrid
&
100Ω
Transformer
Vo
12.5
The driver is biased with a mid supply (nominaly
+6V), in order to maintain the DC component of
the signal at +6V. This allows the maximum dy-
namic range between 0 and +12 V. Several op-
tions are possible to provide this bias supply (such
as a virtual ground using an operational amplifier),
such as a two-resistance divider which is the
cheapest solution. A high resistance value is re-
quired to limit the current consumption. On the
other hand, the current must be high enough to
bias the inverting input of the TS612. If we consid-
er this bias current (5µA) as the 1% of the current
through the resistance divider (500µA) to keep a
stable mid supply, two 47kΩ resistances can be
used.
The input provides two high pass filters with a
break frequency of about 1.6kHz which is neces-
sary to remove the DC component of the input sig-
nal. To avoid DC current flowing in the primary of
the transformer, an output capacitor is used.
The 1µF capacitance provides a path for low fre-
quencies, the 10nF capacitance provides a path
for high end of the spectrum.
In differential mode the TS612 is able to deliver a
typical amplitude signal of 18V peak to peak.
The dynamic line impedance is 100Ω. The typical
value of the amplitude signal required on the line
is up to 12.4V peak to peak. By using a 1:2 trans-
former ratio the reflected impedance back to the
primary will be a quarter (25Ω) and therefore the
amplitude of the signal required with this imped-
ance will be the half (6.2 V peak to peak). Assum-
ing the 25Ω series resistance (12.5Ω for both out-
puts) necessary for impedance matching, the out-
put signal amplitude required is 12.4 V peak to
peak. This value is acceptable for the TS612. In
this case the load impedance is 25Ω for each driv-
er.
7/10
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