TS612 ST Microelectronics, Inc., TS612 Datasheet - Page 7

• Manufacturer Part Number: TS612
• Description: Dual Wideband Op-amp With High Output Current
• Manufacturer: ST Microelectronics, Inc.

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
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.
analog to
digital
digital
treatment
digital to
analog
emission
(analog)
reception
(analog)
LP filter
TS612ID
Line Driver
reception
circuits
high output
current
upstream
impedance
matching
downstream
CIRCUIT
HYBRID
twisted-pair
telephone
line
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
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 (5 A) as the 1% of the current
through the resistance divider (500 A) to keep a
stable mid supply, two 47k
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 1 F 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 100 . 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 (25 ) 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 25
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 25 for each driv-
er.
Vi
Vi
100n
100n
1k
1k
10µ
+12V
GND
a +12V single supply
47k
47k
100n
series resistance (12.5
1/2
1/2
R1
R1
+
+
_
_
Vcc/2
R2
R3
GND
+12V
+12V
GND
12.5
12.5
resistances can be
Vo
Vo
10n
1µ
25
for both out-
Hybrid
&
Transformer
1:2
TS612
7/10