Automatic voice-path switching circuit for a speaker phone telephone set

Claim 2

An electrical switching circuit comprising, in combination, input terminal means (2); output terminal means (4); at least two parallel electrical signal transmission paths between said input and output terminal means, said first path comprising a resistor (R15) and a normally conducting depletion type N channel field effect transistor (TR2) serially connected thereto, and said second path comprising a normally nonconducting bipolar NPN transistor (TR3); means (R20, R21) for supplying a bias voltage to the drain of said field effect transistor and to the emitter of said NPN transistor, thereby simultaneously to establish said conducting and non-conducting states; and means for electrically supplying a gating signal to said transistors, which switches said NPN transistor to its conducting state when the magnitude of the gating signal exceeds said bias voltage, and which switches said field effect transistor into its non-conducting state when the magnitude of the gating signal is less than the bias voltage.

Claim 3

A telephone set comprising, in combination, a microphone; and means, including a transmitting amplifier, for supplying outgoing voice signals generated by said microphone to an office line; a loudspeaker; and means including a receiving amplifier, for supplying incoming voice signals to said loudspeaker; means, responsive to the respective magnitudes of the incoming and outgoing voice signals, for generating a control signal representative of the difference between said magnitudes; first means for electrically connecting said microphone to said transmitting amplifier when said control signal at least equals a predetermined threshold voltage level, said first means comprising, in combination, input terminal means (2); output terminal means (4); at least two parallel electrical signal transmission paths between said input and output terminal means, said First path comprising a resistor (R15) and a normally conducting depletion type N channel field effect transistor (TR2) serially connected thereto, and said second path comprising a normally non-conducting bipolar NPN transistor (TR3); means for supplying said threshold voltage to the drain of said field effect transistor and to the emitter of said NPN transistor, thereby simultaneously to establish said conducting and non-conducting states; and means for electrically supplying said control signal to said transistors, thereby switching said NPN transistor to its conducting state when the magnitude of said control signal exceeds said threshold voltage, and switching said field effect transistor into its non-conducting state when the magnitude of said control signal is less than said threshold voltage; and second means, also responsive to said control signal, for electrically connecting the incoming voice signals to said receiving amplifier only when the magnitude of said control signal falls below said predetermined threshold voltage level.

Claim 4

A telephone set comprising, in combination, a microphone; and means, including a transmitting amplifier, for supplying outgoing voice signals generated by said microphone to an office line; a loudspeaker; and means including a receiving amplifier, for supplying incoming voice signals to said loudspeaker; means, responsive to the respective magnitudes of the incoming and outgoing voice signals, for generating a control signal representative of the difference between said magnitudes; first means for electrically connecting said microphone to said transmitting amplifier when said control signal at least equals a predetermined threshold voltage level, said first means comprising, in combination, input terminal means (2); output terminal means (4); at least two parallel electrical signal transmission paths between said input and output terminal means, said First path comprising a resistor (R15) and a normally conducting depletion type N channel field effect transistor (TR2) serially connected thereto, and said second path comprising a normally non-conducting bipolar NPN transistor (TR3); means for supplying said threshold voltage to the drain of said field effect transistor and to the emitter of said NPN transistor, thereby simultaneously to establish said conducting and non-conducting states; and means for electrically supplying said control signal to said transistors, thereby switching said NPN transistor to its conducting state when the magnitude of said control signal exceeds said threshold voltage, and switching said field effect transistor into its non-conducting state when the magnitude of said control signal is less than said threshold voltage; and second means, also responsive to said control signal, for electrically connecting the incoming voice signals to said receiving amplifier only when the magnitude of said control signal falls below said predetermined threshold voltage level.

Claim 5

The telephone set according to claim 2 wherein said second means includes input terminal means, output terminal means, at least one electrical signal transmission path therebetween, and means for electrically supplying said control signal to said transistor, said path comprising at least one transistor normally biased to a non-conduction state by said threshold voltage, and switching to a conduction state when the magnitude of said control signal is less than said threshold level.

Claim 6

The telephone set according to claim 3 wherein said control signal generating means includes means for deriving a positive d-c signal representative of the outgoing voice signal magnitude, and means for deriving a negative d-c signal representative of the incoming voice signal magnitude; means, including a signal summing network, for amplifying said d-c signals; and an R-C integrating circuit responsive to said amplified d-c signals for deriving said control signal.