xe056lcc Xecom, Inc, xe056lcc Datasheet - Page 8

• Manufacturer Part Number: xe056lcc
• Description: Surface-mount Slim-link Daa For 56k Bps Data Transfer
• Manufacturer: Xecom, Inc

2/4 Wire Conversion:
Two-way communications over a two-wire telephone line requires that the transmit and receive signal share
the available bandwidth. The 2/4 wire convertor separates these signals at the host interface. Most modem
analog front end chips incorporate an internal 2/4 wire convertor.
If you are using the XE056LCC for an application other than a modem, such as audio, or your modem
analog front end does not provide the 2/4 wire convertor, you will need to provide a discrete 2/4 wire
convertor. Figure 12 shows a simple 2/4 wire convertor circuit.
The performance of the 2/4 wire convertor is measured by its Transhybrid Loss. The Transhybrid Loss
shows how much the 2/4 wire convertor attenuates the transmit signal on the received data path. The
circuit above provides a typical Transhybrid Loss of 20 dB. The value of R3 can be changed to improve
the Transhybrid Loss.
The Transhybrid Loss will vary with the quality of the impedance match to the telephone line. The
impedance presented to the telephone line isa a funciton of the impedance matching resistor, RT.
Variations from line to line mean that a perfect impedance match is rarely achieved.
The 2/4 wire convertor also amplifies the transmit and receive signals to compensate for the insertion
loss of the DAA. This circuit provides 6 dB gain of both the transmit and receive signals. The values of
R1 and R2 set the transmit gain. The values of R4 and R5 set the receive gain.
XE056LCC Applications Notes
XECOM
R1=10k
3
2
7
+
_
R2=22k
TL082C
R4=40k
1
6
5
(8)
R5=11K
R6=10K
R3=20k
RT
T1
T2
DAA
XE056LCC