Automatic disconnect circuit for reducing dial pulse distortion and noise in a subscriber carrier telephone system

Claim 2

Apparatus for automatically disconnecting a local subscriber carrier battery charging circuit that is connected, in a subscriber carrier telephone system including a physical subscriber subset and a carrier subscriber subset, through a cable pair to a central office power source from the latter during the off-hook conditions produced on the cable pair by the physical subscriber subset, said apparatus comprising a pair of input terminals for connection to associated lines of a cable pair; a pair of output terminals for connection to associated input terminals of the charging circuit; first means for selectively connecting said output terminals to associated input terminals for connecting the charging circuit through said apparatus to the power source; second means for detecting an off-hook condition produced on the cable pair by a physical subscriber subset; third means responsive to operation of said second-detecting means for opening said first-connecting means to disconnEct the charging circuit from the central office power source; said first-connecting means comprising a first transistor having collector and emitter electrodes electrically connected in series between one input and one output terminal, and having a base electrode electrically connected to said third means; and fourth means connecting the other input and other output terminals thereof, said first transistor being conducting to connect and cut off to disconnect the charging circuit and the power source; and said second-detecting means comprising a Zener diode that is electrically connected across said input terminals, said diode conducting when the voltage applied thereto in response to a line voltage is greater than the Zener breakdown voltage thereof and being cut off when this applied voltage is less than the Zener voltage thereof; said third means being responsive to nonconduction of said diode for driving said first transistor into cutoff to disconnect said 0ne input and one output terminals.

Claim 3

Apparatus according to claim 1 wherein said diode is connected across the input terminals through said third means, the latter comprising a capacitor connected in series with said diode and said input terminals.

Claim 4

Apparatus according to claim 2 wherein said third means comprises a second transistor having collector and emitter electrodes electrically connected between said first transistor base electrode and said fourth-connecting means, and having a base electrode; said Zener diode being electrically connected across said second transistor collector-base junction.

Claim 5

Apparatus for automatically disconnecting a local subscriber carrier battery charging circuit that is connected, in a subscriber carrier telephone system including a physical subscriber subset and a carrier subscriber subset, through a cable pair to a central office power source from the latter throughout the off-hook and dial conditions produced on the cable pair by the physical subscriber subset for reducing dial pulse distortion, said apparatus comprising a pair of input terminals for connection to associated lines of a cable pair; a pair of output terminals for connection to associated input terminals of the charging circuit; first means for selectively connecting said output terminals to associated input terminals for connecting the charging circuit through said apparatus to the power source; second means for detecting an off-hook condition produced on the cable pair by a physical subscriber subset; third means responsive to operation of said second-detecting means for opening said first-connecting means to disconnect the charging circuit from the central office power source; and fourth means for detecting a transient voltage occurring on the cable pair on initiation of a dial pulse in the physical subscriber subset; said third means being responsive to operation of said fourth-detecting means for holding open said first means at the start of a dial pulse for a time interval that is greater than the duration of the break portion of a dial pulse.

Claim 6

Apparatus for automatically disconnecting a local subscriber carrier battery charging circuit that is connected, in a subscriber carrier telephone system including a physical subscriber subset and a carrier subscriber subset, through a cable pair to a central office power source from the latter throughout the off-hook and dial conditions produced on the cable pair by the physical subscriber subset for reducing dial pulse distortion, said apparatus comprising a pair of input terminals for connection to associated lines of a cable pair; a pair of output terminals for connection to associated input terminals of the charging circuit; first means for selectively connecting said output terminals to associated input terminals for connecting the charging circuit through said apparatus to the power source; second means for detecting an off-hook condition produced on the cable pair by a physical subscriber subset; third means responsive to operation of said second-detecting means for opening said first-connecting means to disconnect the charging circuit from the central office power source; and fourth means for detecting a transient voltage occurring on the cable pair on initiation of a dial pulse in the physical subscriber subset; said third means being responsive to operation of said fourth-detecting means for holding open said first means at the start of a dial pulse for a time interval that is greater than the duration of the break portion of a dial pulse.

Claim 7

Apparatus according to claim 4 wherein said first means comprises a first transistor having collector and emitter electrodes connected in series between one input and one output terminal thereof, and having a base electrode electrically connected to said third means; and fifth means electrically connecting said other input and output terminals thereof, said first transistor being conducting to connect and cut off to disconnect the one input and one output terminals thereof; and wherein said fourth-detecting means comprises a first capacitor and first resistor electrically connected in series across said input terminals, and a second transistor having a base-emitter junction connected across said first resistor and having a collector electrode electrically connected to said third means, said second transistor conducting in response to a voltage developed across said first resistor in Response to the transient voltage produced across the input terminals on initiation of a dial pulse by the physical subscriber subset.

Claim 8

Apparatus according to claim 5 wherein said third means comprises a second capacitor electrically connected across the collector-emitter junction of said second transistor, conduction of the latter-second transistor discharging said second capacitor for holding said first transistor cut off.

Claim 9

Apparatus according to claim 6 wherein said second capacitor is electrically connected across the base-emitter junction of said first transistor, said second capacitor having a charge time for charging to the first transistor base-emitter turn-on junction voltage that is greater than the duration of the break portion of a dial pulse for holding said first transistor cut off and thus disconnecting said one input and one output terminals throughout the break portion of a dial pulse.

Claim 10

Apparatus according to claim 7 wherein said third means comprises a third transistor having collector-emitter electrodes resistively electrically connected between said first transistor base electrode and said fifth-connecting means and having a base electrode; wherein said second-detecting means comprises a Zener diode; and including sixth-connecting means resistively electrically connecting said diode in series between the terminal of said second capacitor that is spaced from the one input terminal and the other input terminal and also resistively connecting said diode across the base-collector junction of said third transistor; said diode being conducting when the voltage applied thereto in response to a line voltage is greater than the Zener voltage thereof and being cut off when this line voltage is less than the Zener voltage thereof, nonconduction of said diode cuasing said third transistor to cut off and said second capacitor to discharge to drive said first transistor into cut-off to disconnect the one input and one output terminals thereof.

Claim 11

Apparatus according to claim 5 for disconnecting the input and output terminals thereof and thus the charging circuit from the power source when a ringing voltage to the physical subscriber subset is applied on the cable pair, said apparatus including a Zener diode electrically connected across said first capacitor.

Claim 12

Apparatus according to claim 5 including a diode connected in the reverse direction between said first transistor and said one output terminal.

Claim 13

Apparatus according to claim 8 wherein said fifth connecting means comprises a fourth transistor having emitter-collector electrodes connected in series between the other input and other output terminals and having a base electrode connected in series with said third transistor emitter and collector electrodes.

Claim 14

Apparatus according to claim 5 including a second resistor connected across said first capacitor and providing a leakage path for discharging the latter during the time interval that said first transistor is nonconducting.

Claim 15

Apparatus according to claim 6 wherein said third means comprises a third transistor having emitter and collector electrodes resistively electrically connected in series between said first transistor base electrode and said fifth-connecting means, and having a base electrode electrically connected to the terminal of said second capacitor that is spaced from said one input terminal, said second capacitor being electrically connected across the base-emitter junctions of said first and third transistors which are electrically connected in series.

Claim 16

Apparatus according to claim 13 wherein said second capacitor has a charge time for charging to the sum of the base-emitter junction turn-on voltages of said first and third transistors that is greater than the duration of the break portion of a dial pulse for holding said first transistor cut off throughout the break portion of a dial pulse.

Claim 17

Apparatus according to claim 14 wherein said second means comprises a first Zener diode and sixth mEans resistively electrically connecting said first diode in series between said input terminals and across the base-collector junction of said third transistor.

Claim 18

Apparatus according to claim 15 wherein said fifth means comprises a fourth transistor having emitter and collector electrodes electrically connected in series between said other input and other output terminals and having a base electrode electrically connected in series with the emitter and collector electrodes of said third transistor.

Claim 19

Apparatus according to claim 16 including a second-leakage resistor connected across the base-emitter junction of said fourth transistor.

Claim 20

Apparatus according to claim 17 including a third resistor connected across said first capacitor and providing a leakage path for discharging the latter during nonconduction of said first transistor.

Claim 21

Apparatus according to claim 17 for disconnecting said input and output terminals and thus the charging circuit from the power source during application of a ringing voltage on the cable pair to the physical subscriber subset for reducing noise in a subscriber carrier subset, said apparatus including a second Zener diode electrically connected across said first capacitor.

Claim 22

Apparatus according to claim 19 including a third semiconductor diode connected in the reverse direction between the one of said first and fourth transistors having the third transistor collector electrode connected thereto and the associated output terminal.

Claim 23

A two-port network for disconnecting, upon initiation of a dial pulse by a physical subscriber subset in a subscriber carrier telephone system that also includes a carrier subscriber subset, a local subscriber carrier battery charging circuit that is connected to the output port thereof from a cable pair and central office talking battery that are connected in series to the input port thereof for reducing dial pulse distortion, said network comprising a first-switching transistor having an emitter electrode electrically connected to one terminal of the input port, having a collector electrode electrically connected to one terminal of the output port, and having a base electrode; a second transistor having an emitter electrode connected to said one input terminal and having base and collector electrodes; first-connecting means electrically connecting the other terminals of the input and output ports together; a first capacitor connected across the emitter-collector junction of said second transistor and the emitter-base junction of said first transistor; a first resistor; a second capacitor; second-connecting means connecting said first resistor and said second capacitor in series across the input port with said first resistor connected across the base-emitter junction of said second transistor; a third transistor having collector and emitter electrodes electrically connected in series between said first transistor base electrode and said first-connecting means, and having a base electrode; and third-connecting means resistively electrically connecting the terminal of said first capacitor that is spaced away from the one input terminal to the base electrode of said third transistor and to the other imput terminal; said first capacitor having a charge time for charging to the first-switching transistor base-emitter junction turn-on voltage that is greater than the time interval required for the central office A-pulsing relay contacts to open; said first-switching transistor and said third transistor conducting to pass a charging current from the central office talking battery prior to the physical subscriber telephone subset producing a dial pulse; said second transistor conducting in response to a voltage produced across said first resistor and caused by a transient voltage across the input terminals on the leading edge of a dial pulse to discharge said first capacitor to cut off said first-switching transistor and disconnEct the input and output ports for a time interval that is greater than that required for the central office A-pulsing relay contacts to open.

Claim 24

A two-port network for disconnecting, upon initiation of a dial pulse by a physical subscriber subset in a subscriber carrier telephone system that also includes a carrier subscriber subset, a local subscriber carrier battery charging circuit that is connected to the output port thereof from a cable pair and central office talking battery that are connected in series to the input port thereof for reducing dial pulse distortion, said network comprising a first-switching transistor having an emitter electrode electrically connected to one terminal of the input port, having a collector electrode electrically connected to one terminal of the output port, and having a base electrode; a second transistor having an emitter electrode connected to said one input terminal and having base and collector electrodes; first-connecting means electrically connecting the other terminals of the input and output ports together; a first capacitor connected across the emitter-collector junction of said second transistor and the emitter-base junction of said first transistor; a first resistor; a second capacitor; second-connecting means connecting said first resistor and said second capacitor in series across the input port with said first resistor connected across the base-emitter junction of said second transistor; a third transistor having collector and emitter electrodes electrically connected in series between said first transistor base electrode and said first-connecting means, and having a base electrode; and third-connecting means resistively electrically connecting the terminal of said first capacitor that is spaced away from the one input terminal to the base electrode of said third transistor and to the other imput terminal; said first capacitor having a charge time for charging to the first-switching transistor base-emitter junction turn-on voltage that is greater than the time interval required for the central office A-pulsing relay contacts to open; said first-switching transistor and said third transistor conducting to pass a charging current from the central office talking battery prior to the physical subscriber telephone subset producing a dial pulse; said second transistor conducting in response to a voltage produced across said first resistor and caused by a transient voltage across the input terminals on the leading edge of a dial pulse to discharge said first capacitor to cut off said first-switching transistor and disconnEct the input and output ports for a time interval that is greater than that required for the central office A-pulsing relay contacts to open.

Claim 25

A network according to claim 21 that is symmetrical wherein said first-connecting means comprises a fourth transistor having emitter and collector electrodes electrically connected to the other input and other output terminals, respectively, and having a base electrode electrically connected to one of said third transistor emitter and collector electrodes; wherein said second-connecting means comprises a second resistor connected to the other input terminal and in series with said first resistor and second capacitor; including a fifth transistor having an emitter-base junction connected across said second resistor with the emitter electrode connected to the other input terminal, and having a collector electrode; and wherein said third-connecting means comprises a third capacitor connected across said fifth transistor emitter-collector junction and said fourth transistor emitter-base junction.

Claim 26

The network according to claim 22 including a third resistor connected in parallel with said second capacitor for providing a discharge path for the latter during nonconduction of said first and fourth-switching transistors.

Claim 27

A network according to claim 22 for disconnecting the input and output terminals throughout the off-hook and dialing conditions produced on the cable pair by the physical subscriber subset, wherein said third-connecting means comprises a first Zener diode electrically connected between said first and third capacitor and across the base-collector junction of said third transistor, said first diode being rendered nonconducting for cutting off said third transistor and thus said first and fourth-switching transistors when the line voltage applied thereto drops below the first diode Zener voltage in response to the physical subscriber subset going off-hook.

Claim 28

The network according to claim 24 for disconnecting the input and output terminals thereof in response to a ringing voltage applied on the cable pair to the physical subscriber subset, wherein said second-connecting means comprises a second Zener diode connected across said second capacitor, said second diode conducting when the line voltage applied thereto exceeds its Zener voltage for rendering said second and fifth transistors conducting to discharge the associated first and third capacitors for rendering said first and fourth-switching transistors nonconducting.

Claim 29

Apparatus according to claim 25 including a third semiconductor diode connected in the reverse direction between the one of said first and fourth transistor collector electrodes having the third transistor collector electrode connected thereto and the associated output terminal.

Claim 30

A two-port network for disconnecting, upon initiation of a dial pulse by a physical subscriber subset in a telephone system that also includes a carrier suscriber subset, a local subscriber carrier battery charging circuit that is connected to the output port thereof from a cable pair and central office talking battery that are connected in series to the input port thereof for reducing dial pulse distortion, said network comprising first and second switching transistors having emitter electrodes electrically connected to different terminals of the input port, having collector electrodes electrically connected to different terminals of the output port, and having base electrodes; a third transistor having an emitter electrode connected to the one input terminal that is connected to said first transistor emitter electrode, and having base and collector electrodes; a first capacitor connected across the emitter-collector junction of said third transistor and the emitter-base junction of said first transistor; a first resistor; a second capacitor; first-connecting means connecting said first resistor and second capacitor in series across the input port with said first resistor connected across the base-emitter junction of said third transistor; a fourth transistor having emitter and collector electrodes electrically connected in series between said first and second transistor base electrodes, and having a base electrode; and second-connecting means resistively electrically connecting the terminal of said first capacitor that is spaced away from the one input terminal to the other input terminal and to the base electrode of said fourth transistor; said first capacitor having a charge time for charging to the sum of the first and fourth transistor base-emitter junction turn-on voltages that is greater than the time interval required for the central office A-pulsing relay contacts to open; said first and second-switching transistors and said fourth transistor conducting to pass a charging current from the central office talking battery prior to the physical subscriber telephone subset producing a dial pulse; said third transistor conducting in response to a voltage produced across said first resistor and caused by a transient voltage across the input terminal on the leading edge of a dial pulse to discharge said first capacitor to cut off said first and second-switching transistors and disconnect the input and output ports for a time interval that is greater than that required for the central office A-pulsing relay contacts to open.

Claim 31

A two-port network for disconnecting, upon initiation of a dial pulse by a physical subscriber subset in a telephone system that also includes a carrier suscriber subset, a local subscriber carrier battery charging circuit that is connected to the output port thereof from a cable pair and central office talking battery that are connected in series to the input port thereof for reducing dial pulse distortion, said network comprising first and second switching transistors having emitter electrodes electrically connected to different terminals of the input port, having collector electrodes electrically connected to different terminals of the output port, and having base electrodes; a third transistor having an emitter electrode connected to the one input terminal that is connected to said first transistor emitter electrode, and having base and collector electrodes; a first capacitor connected across the emitter-collector junction of said third transistor and the emitter-base junction of said first transistor; a first resistor; a second capacitor; first-connecting means connecting said first resistor and second capacitor in series across the input port with said first resistor connected across the base-emitter junction of said third transistor; a fourth transistor having emitter and collector electrodes electrically connected in series between said first and second transistor base electrodes, and having a base electrode; and second-connecting means resistively electrically connecting the terminal of said first capacitor that is spaced away from the one input terminal to the other input terminal and to the base electrode of said fourth transistor; said first capacitor having a charge time for charging to the sum of the first and fourth transistor base-emitter junction turn-on voltages that is greater than the time interval required for the central office A-pulsing relay contacts to open; said first and second-switching transistors and said fourth transistor conducting to pass a charging current from the central office talking battery prior to the physical subscriber telephone subset producing a dial pulse; said third transistor conducting in response to a voltage produced across said first resistor and caused by a transient voltage across the input terminal on the leading edge of a dial pulse to discharge said first capacitor to cut off said first and second-switching transistors and disconnect the input and output ports for a time interval that is greater than that required for the central office A-pulsing relay contacts to open.

Claim 32

Apparatus according to claim 27 including a second resistor connected in parallel with said second capacitor for providing a discharge path for the latter during nonconduction of said first and second-switching transistors.

Claim 33

Apparatus according to claim 27 for disconnecting the input and output terminals throughout the off-hook and dialing conditions produced on the cable pair by the physical subscriber subset, wherein said second-connecting means comprises a first Zener diode electrically connected across the base-collector junction of said fourth transistor, said first diode being rendered nonconducting for discharging said first capacitor and cutting off said first and fourth transistors and thus said second transistor when the line voltage applied thereto drops below its Zener voltage in response to the physical subscriber subset going off-hook; said first capacitor having a charge time for charging to the sum of the first and fourth transistor base-emitter junction turn-on voltages that is greater than the duration of the break portion of a dial pulse.

Claim 34

Apparatus according to claim 29 for disconnecting the input and output terminals thereof in response to a ringing voltage applied on the cable pair so the physical subscriber subset, wherein said first-connecting means includes a second Zener diode connected across said second capacitor, said second diode conducting when the line voltage applied thereto exceeds the Zener voltage thereof for rendering said third transistor conducting to discharge said first capacitor for rendering said first and second-switching transistors nonconducting.

Claim 35

Apparatus according to claim 30 including a third semiconductor diode connected in the reverse direction between the one of said first and second transistor collector electrodes having the fourth transistor collector electrode connected thereto and the associated output terminal.