Download TR41.3.5-01-11-039-(word)ParallelSetSimulatorCircuit,SWhitesell

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.