Telephone subscriber line ring-trip detection circuit

Claim 2

A telephone system comprising a transmission network, a plurality of subscriber lines normally connected to respective input terminals of said network, each of said lines including a normally open hookswitch and a ringer circuit, a ringing current circuit for said lines inCluding a source of direct current, a source of alternating ringing current, and a plurality of first voltage dividers associated respectively with said lines; a plurality of relay means individually associated with said lines for disconnecting a selected line of said plurality of lines from said transmission network and for connecting said selected line to a first tap on its associated voltage divider for applying said ringing current to the ringer circuit of said selected line when said selected line is called, and ring trip detection circuit means for detecting a closed hookswitch condition on said selected line comprising a plurality of direct current detection circuits, a plurality of second voltage divider circuits included in said ringing current circuit associated respectively with said detection circuits, and an auxiliary network having a plurality of input terminals connected respectively to second taps on said first voltage dividers and a plurality of output terminals connected respectively to said plurality of detection circuits, said auxiliary network being operable responsive to the determination of an idle one of said detection circuits to complete a bridge path including said idle detection circuit between a second tap of said first voltage divider associated with said selected line and a tap on said second voltage divider associated with said idle detection circuit.

Claim 3

A telephone system as claimed in claim 1 in which said lines are coupled to said transmission network by means of transformers effectively blocking direct current from said last-mentioned network.

Claim 4

A telephone system as claimed in claim 2 in which said auxiliary network comprises a coordinate array of solid state crosspoint devices.

Claim 5

A telephone system as claimed in claim 3 in which said plurality of subscriber lines are greater in number than said plurality of detection circuits.

Claim 6

A telephone system having a common control comprising a plurality of subscriber lines, each including a normally open hookswitch, a transmission network, a common ringing circuit including a direct current source for said subscriber lines, switch means individual to each of said lines operated under control of said common control for switching connections of a selected one of said lines between said network and said ringing circuit, means for detecting a closed hookswitch condition in said selected line comprising first circuit means including said common ringing circuit, a first conducting path connected to said common ringing circuit including a first voltage divider, a second conducting path connected to said common ringing circuit including a second voltage divider, a plurality of voltage level detector means each having a first and a second input, an auxiliary network having a plurality of conducting paths connectable therethrough, one of said last-mentioned paths connecting a tap of said first voltage divider and the first input of a selected one of said voltage level detector means, and second circuit means for connecting a tap of said second voltage divider and the second input of said selected one of said voltage level detector means, said switch means serially connecting the hookswitch of said selected line in said circuit means parallel to said voltage dividers when switching a connection of said last-mentioned line from said transmission network to said ringing circuit.

Claim 7

A telephone system having a common control comprising a plurality of subscriber lines, each including a normally open hookswitch, a transmission network, a common ringing circuit including a direct current source for said subscriber lines, switch means individual to each of said lines operated under control of said common control for switching connections of a selected one of said lines between said network and said ringing circuit, means for detecting a closed hookswitch condition in said selected line comprising first circuit means including said common ringing circuit, a first conducting path connected to said common ringing circuit including a first voltage divider, a second conducting path connected to said common ringing circuit including a second voltage divider, a plurality of voltage level detector means each having a first and a second input, an auxiliary network having a plurality of conducting paths connectable therethrough, one of said last-mentioned paths connecting a tap of said first voltage divider and the first input of a selected one of said voltage level detector means, and second circuit means for connecting a tap of said second voltage divider and the second input of said selected one of said voltage level detector means, said switch means serially connecting the hookswitch of said selected line in said circuit means parallel to said voltage dividers when switching a connection of said last-mentioned line from said transmission network to said ringing circuit.

Claim 8

A telephone system having a common control comprising a plurality of subscriber lines, each including a normally open hookswitch, a transmission network, a common ringing circuit including a direct current source for said subscriber lines, switch means individual to each of said lines operated under control of said common control for switching connections of a selected one of said lines between said network and said ringing circuit, means for detecting a closed hookswitch condition in said selected line comprising a plurality of voltage level detector means each having a first and a second input, an auxiliary netwoRk having a plurality of conducting paths selectively connectable therethrough, circuit means including said common ringing circuit and having a first and a second parallel branch connected to said common ringing circuit and including, respectively, a first and a second voltage divider, and a bridging circuit connected between taps of said first and second voltage dividers, said bridging circuit including a selected one of said auxiliary network conducting paths connected at one end to the tap of said first voltage divider and connected at the other end to the first input of a selected one of said voltage level detector means, said bridging circuit further including circuit means for connecting the second input of said selected one of said voltage level detector means to the tap of said second voltage divider, said switch means connecting the hookswitch of said selected line across said first voltage divider when switching the connection of said last-mentioned line from said transmission network to said ringing circuit.

Claim 9

A telephone system having a common control comprising a plurality of subscriber lines, each including a normally open hookswitch, a transmission network, a common ringing circuit including a direct current source for said subscriber lines, switch means individual to each of said lines operated under control of said common control for switching connections of a selected one of said lines between said network and said ringing circuit, means for detecting a closed hookswitch condition in said selected line comprising a plurality of voltage level detector means each having a first and a second input, an auxiliary netwoRk having a plurality of conducting paths selectively connectable therethrough, circuit means including said common ringing circuit and having a first and a second parallel branch connected to said common ringing circuit and including, respectively, a first and a second voltage divider, and a bridging circuit connected between taps of said first and second voltage dividers, said bridging circuit including a selected one of said auxiliary network conducting paths connected at one end to the tap of said first voltage divider and connected at the other end to the first input of a selected one of said voltage level detector means, said bridging circuit further including circuit means for connecting the second input of said selected one of said voltage level detector means to the tap of said second voltage divider, said switch means connecting the hookswitch of said selected line across said first voltage divider when switching the connection of said last-mentioned line from said transmission network to said ringing circuit.

Claim 10

A telephone system as claimed in claim 6 in which each of said voltage level detector means comprises a comparator circuit for comparing the voltage levels at the taps of said first and second voltage dividers.

Claim 11

A telephone system as claimed in claim 7 in which a connection of said selected subscriber line and said transmission network transmits alternating current signals exclusively.

Claim 12

A telephone system as claimed in claim 6 in which each of said voltage level detector means comprises a comparator circuit for comparing the voltage levels at the taps of respective first and second voltage dividers and for generating an output signal when said voltage levels differ by a predetermined magnitude.

Claim 13

In a telephone system having a transformer coupled transmission network, in combination, a plurality of subscriber lines normally connected to transformer terminals of said network, each of said lines terminating in a normally open hookswitch and a ringer circuit, a ringing circuit for said lines including a direct current source and an alternating ringing current source, individual relay switch means for each of said lines for disconnecting an associated line from said network and for connecting said associated line to said ringing circuit when said line is called to provide a ringing current path including the ringer circuit of said line and a direct current path when the hookswitch of said line is closed, and a ring-trip detection circuit means comprising an individual first voltage divider associated with each of said lines connected to said ringing circuit parallel to a line, said divider having a tap for providing a first output voltage when the hookswitch of the associated line is open and a second output voltage when the hookswitch of the associated line is closed, a plurality of voltage level detector means each having a first and a second input, an auxiliary network having a plurality of input terminals connected respectively to the taps of said individual first voltage dividers and having a plurality of output terminals connected respectively to said first inputs of said plurality of voltage level detector means, said auxiliary network establishing a connection between the tap of a first voltage divider associated with a called line and a first input of a voltage level detector means when said last-mentioned detector means is determined as idle for applying said first and second output voltages to said last-mentioned first input, an individual second voltage divider associated with each of said plurality of voltage level detector means connected to said ringing circuit also parallel to a subscriber line, said divider having a tap for providing a reference output voltage, and means for connecting respectively the taps of said second voltage dividers and the second inputs of said voltage level detector means.

Claim 14

In a telephone system having a transformer coupled transmission network, in combination, a plurality of subscriber lines normally connected to transformer terminals of said network, each of said lines terminating in a normally open hookswitch and a ringer circuit, a ringing circuit for said lines including a direct current source and an alternating ringing current source, individual relay switch means for each of said lines for disconnecting an associated line from said network and for connecting said associated line to said ringing circuit when said line is called to provide a ringing current path including the ringer circuit of said line and a direct current path when the hookswitch of said line is closed, and a ring-trip detection circuit means comprising an individual first voltage divider associated with each of said lines connected to said ringing circuit parallel to a line, said divider having a tap for providing a first output voltage when the hookswitch of the associated line is open and a second output voltage when the hookswitch of the associated line is closed, a plurality of voltage level detector means each having a first and a second input, an auxiliary network having a plurality of input terminals connected respectively to the taps of said individual first voltage dividers and having a plurality of output terminals connected respectively to said first inputs of said plurality of voltage level detector means, said auxiliary network establishing a connection between the tap of a first voltage divider associated with a called line and a first input of a voltage level detector means when said last-mentioned detector means is determined as idle for applying said first and second output voltages to said last-mentioned first input, an individual second voltage divider associated with each of said plurality of voltage level detector means connected to said ringing circuit also parallel to a subscriber line, said divider having a tap for providing a reference output voltage, and means for connecting respectively the taps of said second voltage dividers and the second inputs of said voltage level detector means.

Claim 15

In a telephone system having a transformer-coupled transmission network, the combination as claimed in claim 10 in which sAid plurality of subscriber lines are greater in number than said plurality of voltage level detector means.

Claim 16

In a telephone system having a transformer-coupled transmission network, the combination as claimed in claim 11 in which each of said voltage level detector means comprises a comparator circuit means for comparing the voltage levels at said respective taps of said first and second voltage dividers when said hookswitch of a called subscriber line is closed.