TS634IDT View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
TS634IDT Datasheet PDF : 9 Pages
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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
high output
current
ST70135
ST70134
emission LP filter
(analog)
reception
(analog)
upstream
TS634
Line Driver
VGA
impedance
matching
HYBRID
CIRCUIT
twisted-pair
telephone
line
downstream
TS636
Receiver
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
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 TS634. 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
this case the load impedance is 25Ω 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
an active impedance matching
100n
Vcc+
1k
Vi
+
Vcc+
_
GND
R2
1/2 R1 R3
Vcc/2
1/2 R1 R5
Vi
10µ
100n
1k
GND
R4
+ Vcc+
100n
_
GND
Rs1
Vo°
Vo°
Rs2
1µ
10n
Vo
RL
1:n
Hybrid
& 100Ω
Transformer
Vo
6/9
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