Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The invention is in the field of telephone station apparatus
and more particularly the invention relates to monitoring of operational
status of a telephone line connected to a telephone station apparatus.
Key telephone systems are typically provided on a lease
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basis to a subscriber by ar operating telephone company. Historically the
telephone company has insisted that any station apparatus being connected
to key telephone lines shall also be supplied and connected by the
telephone company. Presently however3 a key telephone system subscriber
is permitted to connect other station apparatus sometimes referred to as
interconnect apparatus, providing that such station apparatus at least
meets a functional specification as defined by a national regulating
authority. For example, in the United States of America3 the regulating
authority is the Federal Communications Commission. In Canada, the
regulating authority is the Department of Communications. Operating
telephone companies are thereby substantially assured that interconnect
apparatus meeting these specifications will not be of any detrimental
effect.
In an instance of an interconnect station apparatus being
connected to a telephone line, for example in a key telephone system, the
station apparatus is required to be able to monitor the supervisory status
of the telephone line. Supervisory status, ON HOOK and OFF HOOK, are
manifest by corresponding greater and lesser potential differences being
i present between tip and ring leads in the telephone line. These potential
; diFferences may be of either forward or reverse polarities. Typically the
ON HOOK status is indicated by an absolute potential difference of at
least 40 volts, and the OFF H~OK status is indicated by an absolute
potential difference of usually less than 24 volts. A lines status sensor
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in the interconnect station apparatus must be capable of distinguishing
,~r, the ON HOOK status and the OFF HOOK status while imparting no significant
.: loading effect upon the telephone line, for example as is required in
'~ accordance with the previously mentioned Functional specifications.
Furthermore, in the case of a plurality of interconnect station apparatus
. . being coupled to the telephone line, as is typical in key telephone
. systems, the sum tota'l of the loading of all the line status sensors must
. not exceed that deFined in the functiona'l specification. For example, if
up to five line status sensors are connected along the telephone line, the
input impedance of each line status sensor is preferably at least 50
'. megohms at each of the tip and ring leads.
. Recent designs of interconnect telephone station apparatus,
~' particularly those designs capable of a data communication function,
; include binary logic circuits energized from power and ground terminals of
' a simple mains power supply. It is preferable that a line status sensor
in the interconnect telephone station apparatus will have a binary logic
circuit compatib'le output, and be operable from the same power supply.
It is an object of the invention to provide a line status
~, sensor for use in a station set such that line monitoring requirements of
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said specifications are met.
.. It is also an object of the invention that a plurality of up
to five of the llne status sensors be connectable along a telephone line
,~ with the combined total loadin~ effect of same being within the
;.............. requirements of said specificat1ons.
A line status sensor in accordance with the invention
includes a first circuit for generdting a reference voltage and first and
second lirnit voltages of negative and positive polarities respectively in
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relation to the reference voltage. A translation circuit is responsive to
forward and reverse potential differences appear ng across a pair of line
terminals and to the reference voltage, for generating a correspondingly
proportional voltage signal of correspondin~ polarity in relation to the
reference voltage. A detection circuit generates an output signal being
of one binary state in response to the voltage signal from the translation
circuit being outside of a range defined in relation to the first and
second limit voltages. The detection circuit ~enerates the output signal
being of another binary state in response to the voltage signal being
within the defined range. The output signal is useful in an associated
telephone station apparatus as an indication of ON HOOK and OFF HUOK
conditions of a telephone line connected at the pair of line terminals.
A plurality of the translation and detection circuits in
combination with the first circuit and corresponding pairs of line
terminals provide a lines status sensor useful for monitoring the ON HOOK
and OFF HOOK conditions at each of the pairs of line terminals.
In an alternate configuration of the line status sensor, the
first circuit is adapted to generate third and fourth limit voltages in
addition to the reference voltage and the first and second limit voltages~
; 20 A second detection circuit similar to the last mentioned detection circuit
is responsive to the third and fourth limit voltages and the voltage
signal from the translation circuit, for detecting potential excursion at
the line terminal which are in excess of typical d.c. energizing
potentials and are consistent with an application of ringing signals to
the telephone line.
A method, in accordance with the invention for generating a
supervisory status logic siynal for use in a telephone station apparatus
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connected to a telephone line7 includes the steps of generating a
reference voltage and one and another limit signals having negative and
positive potentials with respect to the reference voltage. Forward and
reverse potential difFerences, appearing across a pair of leads in the
telephone line are translated into a voltage signal of corresponding
polarity in relation to the reference voltage. A supervisory status logic
signal is generated with one of two binary signal states in response to
the voltage signal being outside of a range being defined in relation to
the first and second limit signals and is generated with the other of the
two binary signal states in response to the voltage signal being within
the defined range.
An example embodiment is described with reference to the
; acco~panying drawings in which:
Figure 1 is a schematic diagram of a lines status sensor for
I use with up to five telephone lines, in accordance with the invention; and
Figure 2 is a graphical representation of operating
characteristics oF a lines status sensor in figure 1.
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The lines status sensor in figure 1 is intended for use in a
' station apparatus being suitable for connection with one or rnore telephone
lines. The lines status sensor provides for ON HOOK and OFF HOOK line
status detection in relation to the one or more telephones lines, while
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having an insignificant loading effect. Signals developed within the line
status sensor in response to ringing si~nals in the one or more telephone
lines are optionally useful for detection of the ringing signals~
The lines status sensor in Figure 1 includes five line
status sensors 1()0, 200, 300, ~00 and 500 connected to a voltage divider
at 10. The line status sensor 100 is illustrated in detail and is
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exemplary of the line status sensors 200 - 500. The line status sensor
100 includes line terminals 101 and 1()2 for connection across a two wire
telephone line, and an output line 103 for coupling TTL compatible signals
indicative of the telephone line status to logic circuitry in the station
apparatus. The line status sensors 2no - 500 each have correspondingly
labelled line terminals (201, 202 - 501, 502) and output lines (203 -
503). For consistency in the description, it is assumed that the terminal
1nl is a tip terminal which is normally connected to a corresponding tip
wire in the telephone line and that the terminal 1n2 is a ring terminal
which is normally connected to a corresponding ring wire in the telephone
line. However, as will become evident, this connection is interchangeable
with no consequence to the line status detection function.
Considering the structure of the line status sensor 100~ it
includes a translation circuit, illustrated at 20, coupled to a detection
circuit, illustrated at 30. The translation circuit is connected to
receive a reference voltage from the voltage divider at 10, and the
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~:~ detection circuit is connected to receive first and second limit voltages
from the voltage divider at 10.
: The voltage divider in this example includes resistors 11,
. 20 12, 13 and 1~ being connected in series from between ground and a power
terminal labelled +12V. The reference voltage is supplied on a lead 15
from a junction of the resistors 12 and 13. The first limit voltage is
supplied, having a potential more negative than that of the reference
voltage, on a lead 16 from a junction of the resistors 11 and 12. The
second limit signal is supplied, having a potential more positive than the
reference voltage, on a lead 17 from a junction of the resistors 13 and
14. Capacitors 18 and 19 connected as shown, provide a filter function
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to remove a.c. noise signals which may be present at the power terminal
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The translation circuit at 20 includes a differential
amplifier 21 having an inverting input cornected in series with a resistor
22 to the line terminal 101, and a non inverting input connected in series
with a resistor 23 to the line terminal 102. The non inverting input is
also connected in series with a resistor 2~ to the lead 15. A resistor 25
is connected in parallel with a capacitor 26 between the inverting input
- and an output of the differential amplifier 21. The resistors 22 and 23
are preferably matched to a tolerance of within plus and minus one percent
and in this example have ohmic values in a range of abou~ 50 to 52
megohms. The resistors 24 and 25 are also preferably matched to a
tolerance of within plus and minus one percent. These tolerances are not
j essential but are preferred for consistent operation in a line status
'` sensor. In this example ohmic values were chosen such that a ratio of the
ohmic values of the resistor 22 and the resistor 25 is about 28 to 1.
This ratio determines the gain of the translation circuit and insures that
the differential amplifier 21 will operate well within its linear range
for ON HOOK telephone line voltages of either forward or reverse
polarities. In addition, a large ratio and l percent component
toierances, as in this example, are of benefit to the in circuit common
mode rejection characteristics of the diFferential ampliFier 21,
particularly if the amplifier is chosen to have input impedances similar
to thQse characteristic of field effect devices. For example,
differential amplifiers available with product code LF347 have been found
to be suitable.
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The detection circuit at 30 includes a diFferential
amplifier 31 having an inverting input connected via a lead 32a to a
cathode of a diode 32, the anode of which is connected to the output of
the differential amplifier 21. The differential amplifier 31 also has a
non inverting input connected in series with a resis~or 34, which is
connected via a lead 33a to an anode of a diode 33, the cathode of which
is connected to the output of the differential amplifier 21. A resistor
35 is connected between the non inverting input and an output of the
differential amplifier 31. The output of the differential amplifier 31 is
also connected in series with a resistor 39 to ground, and connected to an
~;~ anode of a diode 38, the cathode of which is connected to the inverting
.;- input of the differential amplifier 31.
. A buffer amplifier 40 is connected in series with the output
of the differential amplifier 31 to provide adequate current on the lead
103 to satis~y a broad spectrum of load current requirements as might be
found in various station apparatus.
The differential amplifiers 21 and 31 and the voltage
divider are conveniently powered from a power source, not shown, having an
output potential in a range of between about 12 and 12.5 volts. The
buffer amplifier is intended to be powered from a power source, typically
a 5 volt supply, not shown, which is common to logic circuits in the
. associated station apparatus.
Operation of the line status sensor 100 is cliscussed with
. reference to flgure 2 wherein a voltage scale at the left hand side of the
figure includes upper and lower portions. The upper portion is a linear
scale representing a range of from four to eight volts. The lower portion
is a linear scale representing a range oF from zero to minus fifty volts.
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Tip and ring voltages as typically appearing across the tip and ring leads
of a telephone line adjacent a station apparatus are shown in reference to
the lower scale. Corresponding output voltages (VA) generated by the
translation circuit are represented by a line VA shown in reference to the
upper scale and the tip and ring voltages. Lines representing voltages
occurring on the leads 32a and 33a in the detection circui~ are also shown
in reference to the upper scale. Potential differences of about 33 volts
and less appearing across the tip and ring leads correspond to an OFF HOOK
, condition which is represented by an area lying between a pair of vertical
dotted lines extending between areas to the right of the upper and lower
portions. The remaining areas are representative of an ON HOOK condition
which corresponds to potential differences of more than the 33 volts
between the tip and ring leads.
In operation the difference between the tip voltage
appearing at the terminal 101 and the voltage at the output of the
differential amplifier 21 is divided across the resistors 22 and 25. Ring
voltages appearing at the terminal 102 are referenced with respect to the
reference voltage on the lead 15 and are divided across the resistors 23
and 24. The differential amplifier 21 responds to these voltages by
generating a translated voltage VA, at its output, being of a potential to
adjust the voltage at the junction of the resistors 25 and 22 to be very
close if not equal to the voltage at the junction of the resistors 23 and
24~ In the case where the resistors 22 and 23 are each 50 megohms and the
resistors 24 and 25 are each 1.8 megohms, the translated voltage VA
corresponds to the voltage VA illustrated in figure 2.
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The detection circuit responds to the translated voltage VA
at the output of the differential amplifier 21 in accordance with the
potentials of the first and second limit voltages and the conduction
; characteristics of the diodes 32 and 33. Diodes of the silicon
semiconductor type are generally suitable however diodes of other
~ semiconductor materials may well be used providing that either the first
;~ and second limit voltages or the response characteristics of the
translation are altered to compensate for the various different
semiconductor forward conduction voltage drops. In the ON HOOK condition
the voltage on the lead 33a is less than the voltage on the lead 32a and
hence the output of the differential amplifier 31 is near ground
potential. In the OFF HOOK condition the voltage on the lead 33a is
greater than the voltage on the lead 32a and hence the output of the
differential amplifier is positive high. Due to the gating action of the
diodes 32 and 33, the lowest voltage on the lead 32a corresponds to the
potential of the first lirnit signal on the lead 16, and the highest
voltage on the lead 33a corresponds to the potential of the second limit
signal on the lead 17. The resistors 34 and 35 are not essential to the
operation of the detection circuit. These elements are used to provide a
minor hysterisis characteristic in the response of the detection circuit
and thereby prevent any tendency toward oscillation which might otherwise
occur at or near a 33 volt potent~al difference being present between the
terminals 101 and 102~ Resistance values of about 5 Kohms and 1 Mohms in
the example embodiment have been found to provide about 1 to 2 volts of
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hysterisis with respect to volkages between the terminals lol and 102.
This hysterisis is not illustrated in figure 2. The diode 38 is used as a
convenient means to provide negative feed back such that when the output
of the differential amplifier 31 is high, it is limited to a potential one
diode forward voltage drop above the potential on the lead 32a, that is a
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~ potential substantially compatible with a low level logic signal input of
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the buffer amplifier 40.
As before mentioned signals potent1ally useful for detection
of ringing signals are generated in the line status sensor in response to
an application of ringing signals to the telephone line. In the presence
of ringing signals, the differential amplifier 21 produces output voltages
which greatly exceed the range of voltages illustrated by the line VA in
figure 2. One suitable ringing detector includes a detection circuit
similar to the detection circuit at 30 however being supplied with limit
signals for example of 4 and 8~5 volts respectively. Transitions 1n the
output signal of the ringing detection circuit are useful to veri~y the
presence of applied rinying signals having a predetermined standard
` ~ frequency of for example 20 Hz, 16 Hz etc.
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