MSAS-46 - Loop Extender Circuit for the MT8972 DNIC

Application Sheet MSAS-46
Loop Extender Circuit for
the MT8972 DNIC
ISSUE 1
April 1986
The MT8972 expects to receive a composite signal
on LIN (Pin #21) which should be one-half of VLOUT,
plus the sum of the far-end signal, noise and echoes.
The passive circuit (C2, C3, C4, R6, R7 and R8)
supplies one half of the VLOUT with the proper phase
to optimize the internal pre-cancellation.
The
differencing circuit of OP2 forms the external hybrid.
The circuit shown in Figure 1 may be used to extend
the line length over which the MT8972 can operate.
The configuration of the circuit is the same for both
80 kbps and 160 kbps. The component values for
each baud rate are listed in Table 1. Operation has
been achieved with up to 40dB of line attenuation
(measured at 60 kHz for 80 kbps and 120 kHz for
160 kbps). The transmission performance of the
loop extender circuit for a bit error rate of 10-6 is
summarized in Tables 2 and 3.
The circuit shown in Figure 2 illustrates a typical
application of the loop extender circuit. Jumpers
allow the reconfiguration of the circuit from MT8972
alone to MT8972 with loop extender. This switchable
configuration allows the MT8972 and loop extender
circuit to operate on loops with attenuation less than
7dB.
The MT8972 LOUT (Pin #1) signal is pre-equalized
and amplified. It is then passed through the line
termination impedance (CL, RL, RLL) and through
the transformer to the line. The transmitted power on
the line is limited to 10 dBm/120Ω and can be altered
by varying the value of the resistor R2.
R2
C1
LEIN
+VCC
R1
2
6
C4
R7
3
C5
+
4
-VCC
C3
OPI
R8
LEOUT 2
7
_
CL
R4
+VCC
R6
RL
RLL
C2
7
_
2
R3
TR
2:1
6
+
-VCC
4
LEOUT1
3
R5
C7
OP2
C6
Twisted Pair
Copper 24-26
Gauge
Figure 1 - Loop Extender Circuit
A-5
MSAS-46
Application Sheet
R1
R2
R3
R4
R5
R6
R7
R8
RL
OP1,OP2 (Note 1)
24k
75k
20k
20k
10k
360Ω
470Ω
2.7k
430Ω
LF411
C5
C6
C7
47nF
100nF
1µF
TR
5%
5%
1%
1%
10%
2%
2%
5%
2%
(National
Semiconductor)
10%
10%
10%
C1
C2
C3
C4
CL
RLL
80kb
560pF
5.6nF
6.2nF
10nF
12nF
3k
5%
5%
5%
5%
5%
5%
160kb
330pF 5%
3.3nF 5%
3.6nF 5%
5.6nF 5%
15nF 5%
3.9k
5%
Note: VCC = ±10 to ±15V
Transformer
1.
Turns ratio 2:1 (split secondary)
2.
Frequency response - flat passband (+/-3 dB) 10kHz to 500kHz
3.
Primary inductance - 50 mH
4.
DC capability - max. 100mA without transformer saturation
Table 1. Component Values
80 kbps
CONFIGURATION
CABLE
24 AWG
(6.9 dB/km at 60kHz)(Note 2)
26 AWG
(10.0 dB/km at 60kHz)
DNIC to DNIC
0.0 to 5.2 km
0.0 to 3.4 km
DNIC with LEC* to DNIC and LEC
0.9 to 6.5 km
0.65 to 4.1 km
Table 2. Transmission Performance at 80kb (BER = 10-6)
160 kbps
CONFIGURATION
CABLE
24 AWG
(8.0 dB/km at 120kHz)
26 AWG
(11.5 dB/km at 120kHz)
DNIC to DNIC
0.0 to 4.1 km
0.0 to 3.0 km
DNIC with LEC to DNIC and LEC
0.65 to 5.1 km
0.5 to 3.6 km
Table 3. Transmission Performance at 160kb (BER = 10-6)
* LEC = Loop Extender Circuit
Note 1 : The selection criteria for operational amplifier:
-Slew rate SR ≥ 10V/µs
-Output Voltage Swing = 20Vpp for R L = 700Ω
The specified op-amp LF411 can be replaced by LF 353 with supply voltage of ±15V ± 10%.
Note 2 : The attenuation of the cable as specified by Bell System Technical Reference PUB 62411.
A-6
MSAS-46
Application Sheet
CB
LOUT
80 kbps RA = 390Ω CA = 22nF CB = 3.3nF
160 kbps RA = 390Ω CA = 22nF CB = 1.5nF
1
RA
CA
MT8972
+5V
2:1
LIN
21
D1
LEIN
D2
LOOP
EXTENDER
C7
LEOUT 1
Twisted Pair
Copper 24-26
Gauge
LEOUT2
C6
NOTES:
- D1, D2 IN5817 (Schottky)
- Solid jumpers used to connect the loop extender
- Dotted jumpers connect MT8972 without loop extender
100nF
Figure 2 - Typical Application of the Loop Extender
A-7
MSAS-46
Notes:
A-8
Application Sheet
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For more information about all Zarlink products
visit our Web Site at
www.zarlink.com
Information relating to products and services furnished herein by Zarlink Semiconductor Inc. or its subsidiaries (collectively “Zarlink”) is believed to be reliable.
However, Zarlink assumes no liability for errors that may appear in this publication, or for liability otherwise arising from the application or use of any such
information, product or service or for any infringement of patents or other intellectual property rights owned by third parties which may result from such application or
use. Neither the supply of such information or purchase of product or service conveys any license, either express or implied, under patents or other intellectual
property rights owned by Zarlink or licensed from third parties by Zarlink, whatsoever. Purchasers of products are also hereby notified that the use of product in
certain ways or in combination with Zarlink, or non-Zarlink furnished goods or services may infringe patents or other intellectual property rights owned by Zarlink.
This publication is issued to provide information only and (unless agreed by Zarlink in writing) may not be used, applied or reproduced for any purpose nor form part
of any order or contract nor to be regarded as a representation relating to the products or services concerned. The products, their specifications, services and other
information appearing in this publication are subject to change by Zarlink without notice. No warranty or guarantee express or implied is made regarding the
capability, performance or suitability of any product or service. Information concerning possible methods of use is provided as a guide only and does not constitute
any guarantee that such methods of use will be satisfactory in a specific piece of equipment. It is the user’s responsibility to fully determine the performance and
suitability of any equipment using such information and to ensure that any publication or data used is up to date and has not been superseded. Manufacturing does
not necessarily include testing of all functions or parameters. These products are not suitable for use in any medical products whose failure to perform may result in
significant injury or death to the user. All products and materials are sold and services provided subject to Zarlink’s conditions of sale which are available on request.
Purchase of Zarlink’s I2C components conveys a licence under the Philips I2C Patent rights to use these components in and I2C System, provided that the system
conforms to the I2C Standard Specification as defined by Philips.
Zarlink, ZL and the Zarlink Semiconductor logo are trademarks of Zarlink Semiconductor Inc.
Copyright Zarlink Semiconductor Inc. All Rights Reserved.
TECHNICAL DOCUMENTATION - NOT FOR RESALE