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Transcript
TR41.3.5-01-11-039 STANDARDS PROJECT PN-3-4350.110 TITLE Parallel Set Simulator for Transmission Testing SOURCE VTech Advanced American telephones 2 Shannon Ct Howell, NJ 07731 CONTACT Stephen R Whitesell Phone 732 751 1079 Fax 732 751 0095 Email [email protected] DATE October 15, 2001 DISTRIBUTION TR-41.3.5 Abstract In addition to providing a 600 ohm ac termination, the circuit used to simulate a parallel set for purposes of transmission testing should approximate the allowed lower limit offhook dc V-I characteristics with a high degree of accuracy. Simulator circuits proposed in previous contributions, including one by this contributor, fail to do so. A circuit schematic that achieves this goal is proposed. Copyright Notice: The contributor grants a free, irrevocable, non-exclusive license to the Telecommunications Industry Association (TIA) to incorporate text or other copyrightable material contained in this contribution and any modifications thereof in the creation of a TIA Publication; to copyright and sell in TIA’s name any TIA Publication even though it may include all or portions of this contribution; and at TIA’s sole discretion to permit others to reproduce in whole or in part such contribution or the resulting TIA Publication. This contributor will also be willing to grant licenses under such copyrights to third parties on reasonable, non-discriminatory terms and conditions for the purpose of practicing a TIA Publication that incorporates this publication. Disclaimer: This contribution has been prepared by VTech Advanced American Telephones (VTech) to assist the TIA TR-41 Engineering Committee or one of its sub-elements as noted above. It is offered as a basis for discussion and is not to be construed as a binding proposal on VTech. VTech specifically reserves the right to amend or modify the material contained herein, and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of VTech other than as provided in the copyright statement above. Intellectual Property Statement: The individual preparing this contribution is unaware of any patents or published pending patent applications, the use of which may be essential to the practice of all or part of this contribution when incorporated into a TIA Publication. 2 TR41.3.5-01-11-039 Background Contribution TR41.3.5-99-11-023 proposed requirements and a simulator circuit to be used for determining the effect of a parallel set off-hook on transmission performance. The simulator circuit was based on approximating a lower limit V-I characteristic that was being used internally in Lucent Technologies Consumer Products (now VTech Advanced American Telephones) to supplement the information given in TIA/EIA-470-B. However, it does not do a good job of approximating the lower V-I limit proposed in Contribution TR41.3.5-00-08-042. Nor does it do a good job of approximating the revised lower limit V-I characteristic shown in Figure 1 that TR-41.3.5 is proposing to adopt for TIA/EIA-470-C (PN-3-4350). 25 20 Unacceptable Region (47.5, 19) (83.75, 19) 2.5 =5 0•I 40 Set Voltage (Volts) V 15 Undefined Region (106.25, 10) 10 Preferred Region Conditional Region (20, 8) (18, 7.2) (50, 7) 5 Unacceptable Region (20, 4) 0 0 20 40 60 80 100 Set Current (mA) Figure 1: Proposed Off-Hook V-I Template for TIA/EIA-470-C Contribution TR41.3.5-00-11-057 proposed a different parallel set simulator. This proposal is included in Draft 5 of PN-3-4350.110 (Contribution TR41.3.5-01-11-036). It approximates the lower limit V-I characteristic in Contribution TR41.3.5-00-08-042 reasonably well in the region around 20 mA, but deviates somewhat at lower and higher currents. It deviates even further from the lower V-I limit shown in Figure 1. 3 TR41.3.5-01-11-039 Discussion The parallel set simulator used for transmission testing should have dc V-I characteristics representing the minimum effective resistance in order to rob as much current away from the set under test as possible. However, the simulator should be constrained to be representative of products expected to be encountered in real use. This implies the simulator should approximate the lower allowed limit for the off-hook V-I characteristic shown in Figure 1. Since the simulator is used for testing under various loop conditions, it should simulate the characteristic well over the full range of currents likely to be encountered. This simulator should also provide a nominal 600 ohm ac impedance for loading the transmission path. The lower limit curve in Figure 1 consists of three segments which may be described as follows: A 200 ohm resistor for currents between 0 and 20 mA. A 100 ohm resistor with a 2 volt offset for currents between 20 and 50 mA. A 53.3 ohm resistor with a 4.33 volt offset between 50 and 106.25 mA. This limit curve may be realized by the idealized circuit shown in Figure 2. However, low voltage zener diodes are rather far from ideal at low current values and do not have sharp corners to their own V-I characteristics. In addition, 2.0 V zener diodes are difficult to find. T (+) 53.3 46.7 4.33 V 100.0 2.00 V R (–) Figure 2: Idealized Circuit Schematic for Lower Limit V-I Characteristic A more realistic approach is to use forward biased strings of a standard silicon rectifier diode such as the 1N4004. A schematic for a parallel set simulator circuit using this implementation is shown in Figure 3. Although the circuit is polarity sensitive as shown, additional diode strings of the opposite polarity may be added in parallel with the ones shown if desired to eliminate this issue. A 120 C repeat coil is used to provide a balanced 600 ohm ac termination. 4 TR41.3.5-01-11-039 T (+) 39 , 1 W 2 4 47 1 6 3 8 5 7 600 100 R (–) Notes: 1. Circuit is polarity sensitive. 2. Use IN4004, or similar, for diode strings. 3. Resistor values shall be ± 1%. 4. 120 C repeat coil adds approximately 15 resistance w hen connected as show n. 120 C Repeat Coil Figure 3: Implementation of Simulator for Parallel Set Transmission Tests Data comparing the V-I characteristics of the simulator in Figure 3 to those of the simulator currently shown in Figure 4 of Contribution TR41.3.5-01-11-036 and to the actual V-I limit are shown in Table 1. It is clear that the circuit of Figure 3 does a much better job of approximating the lower limit V-I characteristic. If necessary, component values may be adjusted slightly to ensure a good approximation to the V-I limit characteristic. Deviations of less than ± 0.3 V over the 0 to 100 mA current range are readily achievable. Table 1 Current (mA) Limit (V) -036 Fig 4 (V) Deviation (V) Fig 3 (V) Deviation (V) 5 1.00 1.96 .96 1.00 .00 10 2.00 2.68 .68 2.01 .01 15 3.00 3.37 .37 2.99 -.01 20 4.00 4.05 .05 3.82 -.18 25 4.50 4.72 .22 4.46 -.04 30 5.00 5.39 .39 5.00 .00 35 5.50 6.05 .55 5.51 .01 40 6.00 6.71 .71 5.95 -.05 45 6.50 7.38 .88 6.37 -.13 50 7.00 8.03 1.03 6.75 -.25 55 7.27 8.69 1.42 7.10 -.17 60 7.53 9.35 1.82 7.45 -.08 70 8.07 10.65 2.58 8.09 .02 80 8.60 11.94 3.34 8.71 .11 90 9.13 13.22 4.09 9.31 .18 100 9.67 14.50 4.83 9.89 .22 TR41.3.5-01-11-039 5 Proposal Replace Figure 4 in Contribution TR41.3.5-01-11-036 with Figure 3 above. If specification of the 120 C repeat coil is considered a problem because of its limited availability, an “or equivalent” could be added to the figure. The Tellabs 4422 dual repeat coil modules should provide an acceptable equivalent. Another alternative would be to specify the circuit of Figure 3, provide a more generic specification for a split winding audio transformer. If this approach is taken, the value of the 39 ohm resistor should be left as a variable so that it plus the resistance of the transformer windings is approximately 53 ohms. In addition, a tolerance should be placed on the degree to which the simulator’s V-I characteristic approximates the limit curve. This can be accomplished by adding an additional note to the figure that reads as follows: Slight adjustment of component values may be necessary to ensure the dc V-I characteristic of this circuit, as measured at tip and ring, is within ± 0.3 V of the lower limit for the Preferred Region of the off-hook V-I characteristics shown in [proper reference to Figure 3 in PN-3-4350.221] over the range 0 to 100 mA.