Multifrequency oscillator employing solid-state device switching for frequency selection

Claim 2

Oscillatory signal generating apparatus for a subscribers''s telephone set comprising, in combination, an active oscillator circuit element, a feedback path for said element, a first and second group of tuned circuits connected in a mutual parallel relation, said groups being connectable in the feedback path of said element and being connectable across a telephone line, means for selectively connecting the combinations of one of said tuned circuits from said first group and one of said tuned circuits from said second group into said feedback paths thereby to enable the generation of a selected combination of oscillatory bursts, said last-named means comprising a plurality of pairs of switches, each of said pairs comprising a respective series combination of a respective mechanical switch and a respective solid-state switChing device, each of said solid-state switching devices being operated in response to the operation of a corresponding one of said mechanical switches, whereby the quality of generated oscillatory signals is isolated from and unaffected by the distortion products associated with the operation of said mechanical switches, means for regulating the level of direct current passing through said solid-state switching devices, said regulating means comprising a first transistor having the collector electrode thereof connected to a common point of each of said tuned circuits in one of said groups, leaving the emitter electrode thereof connectable to one side of a telephone line by way of a resistive element, means including a varistor connecting the base of said last-named transistor to one side of said line and a resistive element connecting the base of said last-named transistor to the other side of said line.

Claim 3

Oscillatory signal generating apparatus for a subscribers''s telephone set having line terminals comprising, in combination, a transistor oscillator connected across said terminals, first and second groups of tuned circuits connected in parallel relation in the feedback path of said transistor oscillator, a plurality of dual switch means in each of said groups for shorting out selected portions of said tuned circuits thereby to enable the generation of a selected pair of oscillatory signals each corresponding to a particular tuned circuit in a respective one of said groups, each of said dual switch means including a respective transistor leaving the collector emitter path thereof connected to permit the shorting out of selected portions of the tuned circuits in a corresponding one of said groups, each of said dual switch means further including a respective mechanical switch connected in the base circuit of a respective one of said transistors thereby to permit the application of base current to each of the transistors in said dual switch means, rendering said transistors conductive, said mechanical switches being operable by a pushbutton telephone dial, each of said groups of tuned circuits including a respective plurality of serially conducted inductive elements, said collector electrodes of said transistors being connected to respective terminals of said inductive elements, the free terminal of a terminal one of said inductive elements in each of said groups being connected to the collector electrode of a respective regulating transistor, means including a respective resistive element connecting the emitter electrode of each of said regulating transistors to a common one of said line terminals, means including a common resistive element connecting the base electrodes of each of said regulating transistors to one of said line terminals, and means including a serially connected diode and varistor connecting said last-named base electrodes to the other one of said line terminals.

Claim 4

Oscillatory signal generating apparatus for a subscribers''s telephone set having line terminals comprising, in combination, a transistor oscillator connected across said terminals, first and second groups of tuned circuits connected in parallel relation in the feedback path of said transistor oscillator, a plurality of dual switch means in each of said groups for shorting out selected portions of said tuned circuits thereby to enable the generation of a selected pair of oscillatory signals each corresponding to a particular tuned circuit in a respective one of said groups, each of said dual switch means including a respective transistor leaving the collector emitter path thereof connected to permit the shorting out of selected portions of the tuned circuits in a corresponding one of said groups, each of said dual switch means further including a respective mechanical switch connected in the base circuit of a respective one of said transistors thereby to permit the application of base current to each of the transistors in said dual switch means, rendering said transistors conductive, said mechanical switches being operable by a pushbutton telephone dial, each of said groups of tuned circuits including a respective plurality of serially conducted inductive elements, said collector electrodes of said transistors being connected to respective terminals of said inductive elements, the free terminal of a terminal one of said inductive elements in each of said groups being connected to the collector electrode of a respective regulating transistor, means including a respective resistive element connecting the emitter electrode of each of said regulating transistors to a common one of said line terminals, means including a common resistive element connecting the base electrodes of each of said regulating transistors to one of said line terminals, and means including a serially connected diode and varistor connecting said last-named base electrodes to the other one of said line terminals.

Claim 5

Apparatus in accordance with claim 2 including an oscillator excitation switch comprising a mechanical contact of a dial common switch, and means including said last-named switch for providing excitation current to said oscillator only during the time interval between the closing of a set of said dual switch means and the opening of said excitation switch, said excitation switch operation being arranged to follow the operation of any one of said dual switch means.

Claim 6

In a subscribers''s telephone set including a pair of line terminals, in combination, a speech network including a receiver connected across said line terminals, a conductive path extending from a terminal in the hybrid of said speech network and including, in serial relation, a first resistive element, a transmitter, first and second break contacts of a dial common switch, a first and a second group of tuned circuits in parallel relation, said tuned circuits having a common input point and respective output points, respective current regulating means each connecting a corresponding one of said output points to a common one oF said line terminals, third current regulating means connecting a terminal in said second group of tuned circuits to said common one of said line terminals, a transistor oscillator including said tuned circuits connected across said line terminals, a plurality of dual switch means each adapted for selectively connecting a respective one of said tuned circuits to said oscillator thereby to initiate the generation of a corresponding tone signal, each of said dual switch means comprising a respective transistor and a respective mechanical switch, each of said transistors being rendered conductive by the operation of a corresponding one of said mechanical switches, said mechanical switches being operated by the pushbuttons of a pushbutton telephone dial.

Claim 7

In a subscribers''s telephone set including a pair of line terminals, in combination, a speech network including a receiver connected across said line terminals, a conductive path extending from a terminal in the hybrid of said speech network and including, in serial relation, a first resistive element, a transmitter, first and second break contacts of a dial common switch, a first and a second group of tuned circuits in parallel relation, said tuned circuits having a common input point and respective output points, respective current regulating means each connecting a corresponding one of said output points to a common one oF said line terminals, third current regulating means connecting a terminal in said second group of tuned circuits to said common one of said line terminals, a transistor oscillator including said tuned circuits connected across said line terminals, a plurality of dual switch means each adapted for selectively connecting a respective one of said tuned circuits to said oscillator thereby to initiate the generation of a corresponding tone signal, each of said dual switch means comprising a respective transistor and a respective mechanical switch, each of said transistors being rendered conductive by the operation of a corresponding one of said mechanical switches, said mechanical switches being operated by the pushbuttons of a pushbutton telephone dial.

Claim 8

Apparatus in accordance with claim 4 wherein each of said current regulating means comprises a respective transistor having a collector emitter path thereof connected between a respective one of said tuned circuits and said common one of said line terminals.