TS634ID STMicroelectronics, TS634ID Datasheet - Page 6

• Manufacturer Part Number: TS634ID
• Description: Dual Wide Band Operational Amplifier Adsl Line Interface
• Manufacturer: STMicroelectronics

TS634
THE TS634 AS LINE DRIVER ON ADSL LINE
INTERFACE. SINGLE SUPPLY
IMPLEMENTATION WITH PASSIVE OR ACTIVE
IMPEDANCE MATCHING.
THE LINE INTERFACE - ADSL Remote
Terminal (RT):
The Figure1 shows a typical analog line interface
used for ADSL service. On this note, the accent
will be made on the emission path. The TS634 is
used as a dual line driver for the upstream signal.
Figure 1 : Typical ADSL Line Interface
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 TS634 as a remote terminal trans-
mitter in differential mode.
Figure 2 : TS634 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-
6/9
Vi
Vi
ST70135
100n
100n
1k
1k
10µ
+12V
GND
ST70134
a +12V single supply
47k
47k
100n
emission
(analog)
reception
(analog)
1/2
1/2
R1
R1
+
_
+
_
Vcc/2
R2
R3
LP filter
GND
+12V
+12V
GND
TS634
Line Driver
12.5
TS636
Receiver
12.5
high output
current
VGA
Vo
Vo
upstream
10n
1µ
impedance
matching
downstream
25
CIRCUIT
HYBRID
Hybrid
&
Transformer
1:2
twisted-pair
telephone
line
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 TS634. 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
this case the load impedance is 25 for each driv-
er.
For the ADSL upstream path necessary to avoid
any distortion. In this simple non-inverting amplifi-
cation configuration, it will be easy to implement a
Sallen-Key lowpass filter by using the TS634. For
ADSL over POTS, a maximum frequency of
135kHz is reached. For ADSL over ISDN, the
maximum frequency will be 276kHz.
INCREASING THE LINE LEVEL BY USING AN
ACTIVE IMPEDANCE MATCHING
With passive matching, the output signal ampli-
tude of the driver must be twice the amplitude on
the load. To go beyond this limitation an active
maching impedance can be used. With this tech-
nique it is possible to keep good impedance
matching with an amplitude on the load higher
than the half of the ouput driver amplitude. This
concept is shown in Figure 3 for a differential line.
Figure 3 : TS634 as a differential line driver with
Vi
Vi
100n
100n
1k
1k
10
Vcc+
GND
an active impedance matching
100n
1/2
1/2
R1
R1
+
+
_
_
Vcc/2
R2
R3
R5
R4
Vcc+
GND
Vcc+
GND
Vo°
Vo°
Rs1
Rs2
resistances can be
Vo
Vo
10n
1
RL
Transformer
Hybrid
1:n
&
100