Functional Description
2.5.2
Analog Functions
For both receive and transmit direction, a 2:1 transformer is used to connect the ISAC-S
transceiver to the 4 wire S/T interface. The connections are shown in figure 44.
2 : 1
2 : 1
+ 5 V
+ 5 V
SX1
SX1
VDD
VDD
Transmit
Pair
Transmit
Pair
SX2
SR1
SX2
SR1
10 µF
10 µF
PEB 2085
PEB 2086
VSSD
VSSD
2 : 1
2 : 1
Receive
Pair
Receive
Pair
VSSA
VSSA
SR2
SR2
GND
GND
ITS02339
ITS05640
Figure 44
Connection of the Line Transformers and Power Supply to the ISAC®-S
The external transformer of ratio 2:1 is needed in both receive and transmit direction to provide
for isolation and transform voltage levels according to CCITT recommendations.
The equivalent circuits of the integrated receiver and transmitter are shown in figure 45.
The full-bauded pseudo-ternary pulse shaping is achieved with the integrated transmitter
which is realized as a current limited voltage source. A voltage of 2.1 V is delivered between
SX1-SX2, which yields a current of 7.5 mA over 280 Ω.
Semiconductor Group
82
INFINEON [ Infineon ]
