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 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. trading as Zarlink Semiconductor or its subsidiaries (collectively “Zarlink”) is believed to be reliable. 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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