Advance Information
Functional Description
The termination network is an all passive circuit
which allows the DSLIC to interface to the DSL
through a pulse transformer. The equivalent circuit
of the Passive Line Termination Network can be
seen in Figure 3 below.
The PLT consists of two blocks which includes a
hybrid network and a compensator circuit.
The hybrid network is a 2 to 4 wire converter which
provides a large degree of precancellation of the
near end signal while presenting little attenuation to
the far end signal. This is performed using a
summing junction which effectively subtracts the
transmit signal from the receive path.
The compensator circuit, in conjunction with the
transformer, acts as a highpass filter reducing the
low frequency content in the received line signal.
This, in turn, decreases the effects of ISI and near
end echo, and improves the transceiver perfor-
mance.
MH89101
Typical Application
Figure 4 shows a typical connection diagram of the
MT8910 DSLIC and the Passive Line Termination
Circuit. As seen in Figure 4, the PLT is positioned
between the DSLIC and the line pulse transformer.
Two series protection resistors on the secondary of
the line pulse transformer are used to dissipate any
extraneous energy which may be induced onto the
transmission line.
TX
IN +
680 pF
3.3 nF
R
s
= 30.2
Ω
R
b1
1K6
Ω
R
b2
1K
Ω
130 KΩ
RX
OUT +
68K2
Ω
RX
OUT -
130 KΩ
20 KΩ
XFM +
7K8
Ω
20 KΩ
XFM -
680 pF
TX
IN -
3.3 nF
R
b1
1K6
Ω
R
s
= 30.2
Ω
R
b2
1K
Ω
Figure 3 - Passive Line Termination Network
9-31
MITEL [ MITEL NETWORKS CORPORATION ]
