TA0313 Datasheet, PDF (6/9 Pages) STMicroelectronics – STMicroelectronics Solutions for ADSL Line Interfaces

TA0313
STMicroelectronics Solutions for ADSL Line Interfaces
Increasing the line level by using an active impedance matching
With passive matching, the output signal amplitude of the driver must be twice the amplitude on the load.
To go beyond this limitation an active matching impedance can be used. With this technique it is possible
to maintain good impedance matching with an amplitude on the load higher than half of the output driver
amplitude. This concept is shown in Figure 7 for a differential line.
Figure 7: TS613 as a differential line driver with an active impedance matching
100n
+12V
1k
Vi
3k9
3 ₊ ⁸ _+12V
2^_
1
R2
Rs1
Vo°
½ R1
R3
½ R1
Vi
10µ _3k9 100n
1k _GND
100n
6 ^{_ R4}
7
5+
GND
4
R5
Vo°
Rs2
1µ
10n
Vo
25Ω
Vo
1:2
Hybrid
&
100Ω
Transformer
Component calculation
Let us consider the equivalent circuit for a single-ended configuration, as shown in Figure 8.
Figure 8: Single ended equivalent circuit
+
Vi
_
1/2R1
R2
R3
Rs1
Vo°
-1
Vo
1/2RL
For unloaded system, we can assume that currents through R1, R2 and R3 are respectively:
2-_R---V_--1--i_, (_---V_-----i_--R–_-----V_2----o_----°_---) _and (_---V_-----i_-R-+----3-V_-----o_----)
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