®
MH89101
Passive Line Termination Circuit
Advance Information
Features
•
•
•
Passive Line Termination (PLT) for MT8910
DSLIC
High precision trimmed resistors
Excellent resistor matching required to meet
longitudinal balance as specified in ANSI-
T1.601
Compact SIL package
ISSUE 1
August 1991
Ordering Information
MH89101
6 Pin SIL Package
0°C to +70°C
Description
The MH89101 is a thick film hybrid device which is
used in conjunction with the MT8910 to perform two
to four wire conversion and analog signal
conditioning on the received 2B1Q signal.
•
Applications
•
•
•
•
Pair gain system
ISDN NT1 and NT2 interfaces
Digital multiplexers and concentrators
ISDN U-interface terminals
The signal conditioning is necessary to enable the
DSLIC to interface to the Digital Subscriber Line as
defined in ANSI T1.601-1988. The precanceller
block will perform two to four wire conversion and
provide adequate isolation between transmit and
receive paths.
The small size and the precise resistor matching on
the hybrid makes it suitable for line card or terminals
which use the MT8910 2B1Q U-Interface
Transceiver.
TXin +
XFM +
RXout -
Compensator
Circuit
Precanceller
RXout +
XFM -
TXin -
Figure 1 - Functional Block Diagram
9-29
MH89101
Advance Information
TXin +
XFM +
RXout +
RXout -
XFM -
TXin -
1
2
3
4
5
6
(component side)
Figure 2 - Pin Connections
Pin Description
Pin #
1
2
3
4
5
6
Name
TX
in+
XFM+
RX
out+
RX
out-
XFM-
TX
in-
Description
Transmit Line Signal Input.
Must be connected to the L
out+
output of the DSLIC.
Transformer.
Node of the 2 to 4 wire converter which must be connected to the primary of
the line transformer.
Receive Line Signal Output.
Output of the compensator circuit which must be connected
to the L
in+
input of the DSLIC.
Receive Line Signal Output.
Output of the compensator circuit which must be connected
to the L
in-
input of the DSLIC.
Transformer.
Node of the 2 to 4 wire converter which must be connected to the primary of
the line transformer.
Transmit Line Signal Input.
Must be connected to the L
out-
output of the DSLIC.
9-30
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
MH89101
Advance Information
1:1.3
MT8910
L
out +
L
in +
L
in -
L
out -
MH89101
TX
in +
XFM +
RX
out +
RX
out -
XFM -
TX
in -
D3
D1
+ 5V
D2
7mH
D4
5.5 mH
1.5
µF
10Ω ± 10%
Power
Feed/Extract
5.5 mH
10Ω ± 10%
Note:
D1-D4 Schottky Diodes MUR 105
Figure 4 - Typical Connection Diagram
15.24 mm ± 0.51 mm
(0.6" ± 0.020")
10.67 mm ± 0.51 mm
(0.42" ± 0.020")
1
1.45 mm max.
(0.058")
4.45 mm ± 0.39 mm
(0.175" ± 0.015")
2.54 mm ± 0.254 mm
(0.1" ± 0.010")
NOTE:
All dimensions mm (inches)
0.5 mm nominal
(0.020")
Figure 5 - Physical Dimensions
9-32
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