Tone keying circuit for telephone inband signaling system

Claim 2

In a telephone dial pulse signaling system, apparatus for converting first and second d.c. signaling voltage levels into in-band tone signals comprising: a tone source; a signaling control means responsive to the first and second d.c. signaling voltage levels to provide output signals having, respectively, either a first state or a second state; a voice-frequency path; tone keying means connected between said tone source and said path, said keying means operative to interrupt said tone source in response to signals having one said state from said control means; and shunting means operatively connected to said keying means and responsive to said control means and said other signal state for enhancing said tone source output level for a predetermined time interval.

Claim 3

Apparatus in accordance with claim 1 in which said signaling control means further comprises: a voltage divider having its input connected to receive said first and second signaling voltage levels; and an inverter having its input connected to the output of said voltage divider and having an output connected to the tone keying means whereby a control signal having the required signals having either a first state or a second state is obtained. 3. Apparatus in accordance with claim 1 in which said tone keying means further comprises: an input connected to said tone source; impedance matching means in the transmission path of said tone keying means; gating means connected to said impedance matching means, said gating means passing and interrupting the tone signal applied to said transmission path in response to control signals of said one state; and coupling means having an input connected to said transmission path and an output connected to said voice frequency path.

Claim 4

Apparatus in accordance with claim 3 in which said coupling means further comprises: a voice frequency transformer having a center tapped primary winding and a secondary winding, said primary winding being connected to the output of said gating means and said center tap being connected to said signaling control means; a capacitor connected across the primary winding, said capacitor being resonant with the inductance of said transformer at the frequency of the tone source, thereby causing a high impedance at the tone frequency; and a pair of equal valued resistors, one in each leg of the secondary of said transformer to connect the secondary to the voice frequency path, said resistors being selected to minimize the bridging loss to said path.

Claim 5

Apparatus in accordance with claim 4 in which said gating means comprises a pair of diodes, one in each leg of the tone keyer transmission path.

Claim 6

Apparatus in accordance with claim 4 in which said impedance matching means comprises a pair of equal valued resistors, one in each leg of said tone keyer transmission path, each said resistor being selected to be equal to one-half of the reflected impedance of said coupling transformer to obtain maximum power transfer from the tone signal source to the voice transmission path.

Claim 7

Apparatus in accordance with claim 1 in which said shunting means further comprises: timing means having an input connected to said control means and an output; switching means having an input connected to the output of said timing means and having two outputs, one said output being connected to one leg and the other output being connected to the other leg of the tone keyer transmission path, said switching means being responsive to said timing means and said control means so that said switching means is turned off by said other state of said output signal and is held in this condition by said timing means for said predetermined time interval thereby enhancing the level of the tone signal for the predetermined time interval.

Claim 8

Apparatus in accordance with claim 7 in which said timing means further comprises: a transistor having base, emitter and collector electrodes said collector being operatively connected to the input of said switching means; a voltage divider consisting of two resistors having one end of each resistor connected together forming a voltage divider junction, the opposite end of one said resistor connected to a voltage of one potential and the opposite end of said other resistor connected to a voltage of a different potential, and having said junction connected to the base of said transistor thereby supplying a base bias voltage; a timing resistor having one end connected to the positive d.c. potential of said voltage divider; and a capacitor having one lead connected to the output of the signaling control means and the other lead connected to the other end of said timing resistor and to the emitter of said transistor and supplying a bias thereto for controlling conduction of the transistor and thereby the switching means to enhance the tone signal for said predetermined time interval.

Claim 9

Apparatus in accordance with claim 7 in which said timing means further comprises: a timing resistor having one end connected to a positive potential and its other end connected to the input of said switching means; and a timing capacitor having one end connected to said signaling control meaNs and the other end connected to the input of said switching means so that the switching means is responsive to said control means and said timing capacitor.

Claim 10

Apparatus in accordance with claim 9 in which said switching means further comprises: a pair of transistors each having base, emitter and collector electrodes, said emitters being connected together and to a source of negative d.c. potential; a first shunting resistor having one end connected to one leg of the tone keyer transmission path and the other end connected to the collector of one transistor of the pair; a second shunting resistor having one end connected to the other leg of the tone keyer transmission path and the other end connected to the collector of the other transistor of said pair; a first base bias resistor connected at one end to the base of said one transistor of said pair and the other end connected to the input of said switching means; and a second base bias resistor connected at one end to the base of said other transistor of said pair and the other end connected to the input of said switching means.

Claim 11

Apparatus in accordance with claim 3 in which said gating means further comprises: a first pair of diodes positioned in the transmission path of the tone keying means, one in each leg and each poled to be back biased when the control signal is of one said state; and a second pair of diodes positioned in shunt across the transmission path of the tone keying means and each arranged to conduct when the control signal is of one said state.

Claim 12

In a telephone dial pulse signaling system, apparatus for converting first and second d.c. signaling voltage levels into tone signals comprising: a tone source; a voice-frequency path; a signaling control means responsive to the first and second d.c. signal voltage levels to provide output signals having, respectively, either a first state or a second state; a tone keying means, connected between said tone source and said v-f path, comprising: a transmission path having an input and an output, an input coupling means having an input connected to the tone source and an output connected to the input of the transmission path, a switching means connected across said transmission path, said switching means providing a shunt path when said switch is operated; a timing means connected to said switching means and to said control means, said timing means being activated to effectively open said shunt path for a predetermined time interval when the output from the control means first changes from the second state to the first said state, to provide an enhanced tone burst during the dial signaling interval; a gating means in series with said transmission path, said gating means responsive to the output of said control means to turn the enhanced tone signal on and off in response to the first and second output states from said control means; and an output coupling means operatively connecting the output of said transmission path to the voice frequency path.

Claim 13

In a telephone dial pulse signaling system, apparatus for converting first and second d.c. signaling voltage levels into tone signals comprising: a tone source; a voice-frequency path; a signaling control means responsive to the first and second d.c. signal voltage levels to provide output signals having, respectively, either a first state or a second state; a tone keying means, connected between said tone source and said v-f path, comprising: a transmission path having an input and an output, an input coupling means having an input connected to the tone source and an output connected to the input of the transmission path, a switching means connected across said transmission path, said switching means providing a shunt path when said switch is operated; a timing means connected to said switching means and to said control means, said timing means being activated to effectively open said shunt path for a predetermined time interval when the output from the control means first changes from the second state to the first said state, to provide an enhanced tone burst during the dial signaling interval; a gating means in series with said transmission path, said gating means responsive to the output of said control means to turn the enhanced tone signal on and off in response to the first and second output states from said control means; and an output coupling means operatively connecting the output of said transmission path to the voice frequency path.

Claim 14

Apparatus in accordance with claim 12 in which said signaling control means further comprises: a voltage divider having its input connected to receive the first and second d.c. signaling voltage levels; and an inverter having its input connected to the output of said voltage divider and having an output connected to the tone keying means whereby a control signal having the required output states is obtained.

Claim 15

Apparatus in accordance with claim 12 in which said output coupling means further comprises: a voice-frequency transformer having a center tapped primary winding and a secondary winding, said primary winding being connected to the output of said transmission path and said center tap being connected to said signaling control means; a capacitor connected across the primary winding, said capacitor being resonant with the inductance of said transformer at the frequency of the tone source, thereby causing a high impedance at the tone frequency; and a pair of equal valued resistors, one in each leg of the secondary of said transformer to connect the secondary to the voice-frequency path, said resistors being selected to minimize the bridging loss to said path.

Claim 16

Apparatus in accordance with claim 14 in which said transmission path further comprises: impedance matching means comprising a second pair of equal valued resistors, one in each leg of said transmission path, each said resistor being selected to be equal to one-half of the reflected impedance of the output coupling transformer to obtain maximum power transfer from the tone signal source to the voice-frequency path.

Claim 17

Apparatus in accordance with claim 12 in which said timing means further comprises: a transistor having base, emitter and collector electrodes, said collector being operatively connected to the input of said switching means; a voltage divider consisting of two resistors having one end of each resistor connected together forming a voltage divider junction, the opposite end of one said resistor connected to a voltage of one potential and the opposite end of said other resistor connected to a voltage of a different potential, and having said junction connected to the base of said transistor, thereby supplying a base bias voltage; a timing resistor having one end connected to the positive d.c. potential of said voltage divider; and a capacitor having one lead connected to the output of the signaling control means, and the other lead connected to the other end of said timing resistor and to the emitter of said transistor and supplying a bias thereto for controlling conduction of the transistor and thereby the switching means to enhance the tone signal for said predetermined time interval.

Claim 18

Apparatus in accordance with claim 16 in which said timing means further comprises: a timing resistor having one end connected to a positive potential and its other end connected to the input of said switching means; and a timing capacitor having one end connected to said signaling control means and the other end connected to the input of said switching means so that the switching means is responsive to said control means and said timing capacitor.

Claim 19

Apparatus in accordance with claim 17 in which said switching means further comprises: a pair of transistors each having base, emitter and collector electrodes, said emitters being connected together and to a source of negative d.c. potential; a first shunting resistor having one end connected to one leg of the tone keyer transmission path and the other end connected to the collector of one transistor of the pair; a second shunting resistor having one end connected to the other leg of the tone keyer transmission path and the other end connected to the collector of the other transistor of said pair; a first base bias resistor connected at one end to the base of said one transistor of said pair and the other end connected to the input of said switching means; and, a second base bias resistor connected at one end to the base of said other transistor of said pair, and the other end connected to the input of said switching means.