Abstract A two-tone generator having switching transistors in two LC resonance circuits each composed of a coil and a capacitor for producing a dial tone in the form of two-tone signal by switching the value of the inductances of the coils in response to the control of each of a pair of push-button switches, in which only one make contact is actuated in response to the depression of each push button, so that the ON-OFF output of the contact is employed to control a desired one of a pair switching transistors in each of the two resonance circuits for determining the oscillation frequencies of the two-tone generator associated with the two LC resonance circuits. The switching transistors are coupled with the two LC resonance circuits to switch the value of the inductance of each coil in response to the turn-ON of the collector-emitter path thereof. Each of the switching transistors is turned-ON by flowing a base current greater than the peak value of the AC signal in the resonance circuit without flowing any DC current in the collector-emitter path thereof.
A two-tone generator for producing a dial tone in the form of two-tone signal, comprising: a two-tone oscillator having two LC resonance circuits each composed of a primary coil and a secondary coil and a capacitor in parallel with said secondary coil; a plurality of switching transistors having the collectoremitter paths thereof coupled between corresponding taps along respective ones of said secondary coils and said capacitors to switch the values of the inductances of the secondary coils in response to turning-ON of ones of said switching transistors; a plurality of switches individually controllable and each having a contact operable to an open and a closed condition; a matrix connected to the contacts of the switches for providing outputs corresponding to closed contacts of the switches; and biasing means electrically coupled to said matrix and said switching transistors for biasing the bases of respective selected ones of said switching transistors of the two LC resonance circuits with base currents sufficient to turn-ON said selected ones of said switching transistors in response to said outputs of the matrix.
Claim 2
Dependent Claim
176 words
A two-tone generator for producing a dial tone in the form of two-tone signal, comprising: a two-tone oscillator having two LC resonance circuits each composed of a primary coil and a secondary coil and a capacitor in parallel with said secondary coil; a plurality of switching transistors having the collectoremitter paths thereof coupled between corresponding taps along respective ones of said secondary coils and said capacitors to switch the values of the inductances of the secondary coils in response to turning-ON of ones of said switching transistors; a plurality of switches individually controllable and each having a contact operable to an open and a closed condition; a matrix connected to the contacts of the switches for providing outputs corresponding to closed contacts of the switches; and biasing means electrically coupled to said matrix and said switching transistors for biasing the bases of respective selected ones of said switching transistors of the two LC resonance circuits with base currents sufficient to turn-ON said selected ones of said switching transistors in response to said outputs of the matrix.
Claim 3
Dependent Claim
112 words
A two-tone generator according to claim 1, further including: first diodes each having a cathode connected to the base of a respective one of the switching transistors of the two LC resonance circuits, at least one second diode connected in series through a transmitter with said biasing means, said first diodes being connected to the terminal of the second diode opposite to the diode terminal connected to the transmitter, and switching elements connected between said resonance circuits and said biasing means and biased to conduct when none of the switch contacts are closed for supplying DC currents to the respective secondary coils of the two LC resonance circuits through said switching transistors.
Claim 4
Dependent Claim
31 words
A two-tone generator according to claim 2, further comprising a transistor connected through the second diode with the biasing means for controlling the supply of a DC current to the transmitter.