Speaker telephone

Claim 2

In a speaker telephone having a microphone and an associated microphone amplifier, a speaker, an incoming amplifier for amplifying incoming signals for reproduction by said speaker, and a hybrid network for coupling a signal from said microphone amplifier to a telephone line and for coupling signals from said telephone line to said incoming amplifier, the improvement therewith of: a diode connected in series between the output of said microphone amplifier and said hybrid network, a transistor switch, having a control element, shunted across the input of said incoming amplifier, a control circuit receiving as separate inputs both the output of said microphone amplifier and the output of said incoming amplifier and providing a common control signal to both said diode and the control element of said transistor switch, occurrence of said common control signal causing said transistor switch to disable the input of said incoming amplifier, and forward biasing said diode to permit signal flow therethrough from said microphone amplifier to said hybrid network, said control circuit comprising; a first transistor, having a control electrode, connected to amplify the output received from said microphone amplifier, first rectifier means for rectifying the amplified signal from said first transistor to provide said rectified signal as said control signal, and control means, connected to the control electrode of the first transistor, for permitting amplification by said first transistor to begin only in the absence of an output from said incoming amplifier, said control means comprising; second rectifier means for rectifying the output of said incoming amplifier, and a second transistor biased on by the rectified output from said second rectifier means and connected to the control electrode of the first transistor to disable amplification by said first transistor when said second transistor is biased on.

Claim 3

A speaker telephone according to claim 1 wherein said first and second transistors are of complementary types, the non-control elements of said second transistor being series connected between a source of dc potential and one non-control element of said first transistor, a current sample from the other non-control element of said first transistor being supplied in series with said rectified incoming amplifier output to the control element of said second transistor, whereby said second transistor establishes the bias level of said first transistor in the absence of output signals from either said microphone amplifier or said incoming amplifier, and whereby gain control of said first transistor is achieved.

Claim 4

A speaker telephone according to claim 2 wherein said first and second rectifier means each comprise a germanium diode rectifier and a resistor-capacitor fIlter for filtering the rectified signal.

Claim 5

A speaker telephone according to claim 2 wherein said first transistor is an NPN type, wherein said second transistor is a PNP type, and wherein the collector of said second transistor is connected to the emitter of said first transistor.

Claim 6

A speaker telephone according to claim 4 wherein the collector of said first transistor is connected to said dc source via the primary of a first transformer and a first resistor, and wherein said first rectifier means comprises a diode connected to the secondary of said first transformer and a capacitor and resistor connected to filter the rectified signal from said diode.

Claim 7

A speaker telephone according to claim 5 wherein said incoming amplifier has an output transformer with two secondary windings, said speaker being connected to one of said secondary windings, said rectifier means comprising: a diode connected between one terminal of the other secondary winding and the base of said second transistor, a resistor connected between the other terminal of said other secondary winding to the junction of said first transformer primary and said first resistor, and a capacitor connected between the base of said second transistor and said junction.

Claim 8

A speaker telephone according to claim 6 wherein said incoming amplifier has a push-pull output stage with two primary windings on said output transformer, both primary windings having the same number of turns, and wherein the turns ratio between either primary winding and said one secondary winding is 2:1 and between either primary winding and said other secondary winding is 2:3.

Claim 9

A speaker telephone according to claim 2 wherein said transistor switch comprises a PNP type, germanium transistor having its emitter and collector connected effectively to short out the input of said incoming amplifier when said germanium transistor conducts, said germanium transistor normally being base biased off, said control signal being connected to the base of said germanium transistor so that occurrence of said control signal biases said germanium transistor into conduction.

Claim 10

A speaker telephone according to claim 2 wherein said diode is germanium and is series connected between the output of said microphone amplifier and said hybrid network, said control signal being connected to said diode so that occurrence of said control signal forward biases said diode.

Claim 11

A control circuit for a speaker telephone of the type wherein an amplified microphone signal is transmitted to a telephone line via a hybrid network and wherein audio from the telephone line is supplied via said hybrid network and an amplifier to a loudspeaker, said control circuit comprising: a first transistor connected to amplify said microphone signal, the amplified signal being rectified to provide a control signal, a second transistor interconnected to disable amplification by said first transistor to inhibit provision of said control signal, in response to occurrence of an output from said amplifier, and control means for enabling transmission of said amplified microphone signal and for inhibiting amplification of said incoming audio during occurrence of said control signal, and wherein said first and second transistors are of complementary type, wherein the collector of said second transistor is connected to the emitter of said first transistor, wherein the rectified output of said amplifier is supplied to the base of said second transistor, and wherein a sample of the first transistor collector current is supplied to the base of said second transistor together with said rectified output.

Claim 12

A control circuit for a speaker telephone of the type wherein an amplified microphone signal is transmitted to a telephone line via a hybrid network and wherein audio from the telephone line is supplied via said hybrid network and an amplifier to a loudspeaker, said control circuit comprising: a first transistor connected to amplify said microphone signal, the amplified signal being rectified to provide a control signal, a second transistor interconnected to disable amplification by said first transistor to inhibit provision of said control signal, in response to occurrence of an output from said amplifier, and control means for enabling transmission of said amplified microphone signal and for inhibiting amplification of said incoming audio during occurrence of said control signal, and wherein said first and second transistors are of complementary type, wherein the collector of said second transistor is connected to the emitter of said first transistor, wherein the rectified output of said amplifier is supplied to the base of said second transistor, and wherein a sample of the first transistor collector current is supplied to the base of said second transistor together with said rectified output.

Claim 13

A control circuit according to claim 10 wherein said control means comprises: a diode series connected in the transmission path of said amplified microphone signal, said diode being forward biased into conduction by said control signal, and a transistor switch connected effectively to short out the input to said ampliFier when said switch is turned on by occurrence of said control signal, and wherein the control signal is filtered by a first resistor-capacitor network and wherein the rectified output of said amplifier is filtered by a second resistor-capacitor network, the time constants of said resistor-capacitor networks establishing the break-in times for said speaker telephone.

Claim 14

In a speaker telephone in which audio incoming from a telephone line is amplified by an amplifier, the improvement comprising: circuit means connecting said telephone line to the input of said amplifier, so that said incoming audio will be amplified by said amplifier only when said amplifier input is not shorted out, a germanium transistor connected across the input of said amplifier with a dc emitter-to-collector voltage of zero, and control means for providing base bias to said germanium transistor during speech transmission from said speaker telephone, said bias causing the collector-to-emitter impedance to drop to a level at which the input to said amplifier is effectively shorted out so that said incoming audio will not be amplified by said amplifier during speech transmission.

Claim 15

In a speaker telephone in which audio incoming from a telephone line is amplified by an amplifier, the improvement comprising: circuit means connecting said telephone line to the input of said amplifier, so that said incoming audio will be amplified by said amplifier only when said amplifier input is not shorted out, a germanium transistor connected across the input of said amplifier with a dc emitter-to-collector voltage of zero, and control means for providing base bias to said germanium transistor during speech transmission from said speaker telephone, said bias causing the collector-to-emitter impedance to drop to a level at which the input to said amplifier is effectively shorted out so that said incoming audio will not be amplified by said amplifier during speech transmission.

Claim 16

A control circuit for a speaker telephone of the type having a microphone and an associated microphone amplifier, a loudspeaker, a loudspeaker amplifier for amplifying signals incoming from a telephone line for reproduction by said speaker, and a hybrid network for coupling signals from said telephone line to said loudspeaker amplifier, said control circuit comprising first and second complementary transistors respectively receiving the outputs of said microphone amplifier and said loudspeaker amplifier, and wherein: a. said second transistor is connected to receive at its base, in addition to said loudspeaker amplifier output, a sample of the emitter-to-collector current of said first transistor, an emitter of one of said transistors being connected to the collector of the other of said transistors so as to establish the bias level of said first transistor in the absence of signals from either said microphone amplifier or said loudspeaker amplifier, b. said first transistor, in the absence of an output from said loudspeaker amplifier, being available to amplify speech from said microphone amplifier, the resultant output of said first transistor being rectified by a rectifier to produce a control signal operative to forward bias a diode interconnecting said microphone amplifier and said hybrid network so as to enable microphone speech transmission via said hybrid network to the telephone line and to switch on a transistor switch connected across the input of said loudspeaker amplifier, the resultant low collector-to-emittor impedance of said transistor switch inhibiting the input to said loudspeaker amplifier of incoming signals from said telephone line, and wherein c. in the absence of speech from said microphone amplifier, received speech output from said loudspeaker amplifier causes said second transistor to increase conduction, clamping said first transistor near cut-off so as to prevent amplification by said first transistor and hence to inhibit production of said control signal, so that said diode will block passage of said outgoing speech to said hybrid network, and so that said transistor switch will stay off permitting continued amplification by said loudspeaker amplifier of incoming speech.

Claim 17

A control circuit for a speaker telephone of the type having a microphone and an associated microphone amplifier, a loudspeaker, a loudspeaker amplifier for amplifying signals incoming from a telephone line for reproduction by said speaker, and a hybrid network for coupling signals from said telephone line to said loudspeaker amplifier, said control circuit comprising first and second complementary transistors respectively receiving the outputs of said microphone amplifier and said loudspeaker amplifier, and wherein: a. said second transistor is connected to receive at its base, in addition to said loudspeaker amplifier output, a sample of the emitter-to-collector current of said first transistor, an emitter of one of said transistors being connected to the collector of the other of said transistors so as to establish the bias level of said first transistor in the absence of signals from either said microphone amplifier or said loudspeaker amplifier, b. said first transistor, in the absence of an output from said loudspeaker amplifier, being available to amplify speech from said microphone amplifier, the resultant output of said first transistor being rectified by a rectifier to produce a control signal operative to forward bias a diode interconnecting said microphone amplifier and said hybrid network so as to enable microphone speech transmission via said hybrid network to the telephone line and to switch on a transistor switch connected across the input of said loudspeaker amplifier, the resultant low collector-to-emittor impedance of said transistor switch inhibiting the input to said loudspeaker amplifier of incoming signals from said telephone line, and wherein c. in the absence of speech from said microphone amplifier, received speech output from said loudspeaker amplifier causes said second transistor to increase conduction, clamping said first transistor near cut-off so as to prevent amplification by said first transistor and hence to inhibit production of said control signal, so that said diode will block passage of said outgoing speech to said hybrid network, and so that said transistor switch will stay off permitting continued amplification by said loudspeaker amplifier of incoming speech.