Telephone transceiver with amplified microphone and speaker

Claim 2

In a telephone transceiver of the type employing an amplified loudspeaker and an amplified microphone within the same housing, the improvement comprising: transformer means, said transformer means including a centertapped primary winding and a secondary winding; means for coupling the secondary winding of said transformer means to the loudspeaker, said coupling means including first amplifier means having a pair of input terminals connected to opposite ends of said transformer means secondary winding; first connecting means connecting a first end of said transformer means primary winding to a first terminal of a two wire telephone network; balancing circuit means for connecting the second end of said transformer means primary winding to the second terminal of a two wire telephone network; second amplifier means having input terminals and a pair of output terminals, said second amplifier means input terminals being connected to the microphone, said second amplifier means including an output stage connected across said output terminals and having the operatIng characteristics of a variable resistance, said second amplifier means providing a modulated direct current output signal in response to a modulated input signal received from the microphone; second connecting means for connecting a first of said second amplifier means output terminals to the second telephone network terminal; and third connecting means for connecting the other of said second amplifier means output terminals to the center-tap of said transformer means primary winding, said second amplifier means modulating the transformer means primary winding direct current to produce currents which are equal and in phase in both halves of said center-tapped primary winding, the magnetic fields generated by said in-phase currents being substantially mutually cancelling so that there will be no current induced in the transformer secondary winding.

Claim 3

The apparatus of claim 1 wherein said second amplifier means comprises: a superimposed modulation amplifier having a pair of input terminals and a pair of output terminals, the microphone being connected across said superimposed modulation amplifier input terminals.

Claim 4

The apparatus of claim 2 wherein said second amplifier means further comprises: first rectifier means, said first rectifier means having a first polarity output terminal connected to the second telephone network terminal by said first connecting means, said first rectifier means having a second polarity terminal connected to the center tap of said transformer means primary winding, said rectifier means first and second polarity terminals forming said second amplifier means output terminals, said first rectifier means deriving direct current power from the telephone line for operating said superimposed modulation amplifier; means for delivering direct current power derived from the telephone line by said first rectifier means to said superimposed modulation amplifier; and means for connecting said superimposed modulation amplifier output terminals to opposite polarity terminals of said first rectifier means whereby said superimposed modulation amplifier will modulate direct current flowing through said transformer means primary winding.

Claim 5

The apparatus of claim 3 wherein said first amplifier means comprises: a differential amplifier.

Claim 6

The aparatus of claim 3 further comprising: second rectifier means connected to the telephone network, said second rectifier means providing direct current power for operating said first amplifier means; and means for delivering current from said second rectifier means to said first amplifier means.

Claim 7

The apparatus of claim 3 wherein said superimposed modulation amplifier comprises: means for receiving and amplifying modulated signals received from the microphone; continuously conductive modulator means, said modulator means being connected between a pair of oppositely polarized terminals of said first rectifier means and at least in part defining said second amplifier means output stage, said modulator means including a semiconductor which functions as a variable resistance; and means applying amplified microphone signals from said receiving and amplifying means to said modulator means whereby the current delivered to said modulator means from said first rectifier means will be modulated in accordance with the signals received from the microphone.

Claim 8

The apparatus of claim 6 wherein said modulation amplifier further comprises: isolation circuit means connecting said amplifying means in parallel with said modulator means whereby the voltage for operation of said amplifying means will be developed across said modulator means and current for the microphone will be supplied via said first rectifier means.

Claim 9

The apparatus of claim 7 further comprising: second rectifier means connected to the telephone network, said second rectifier means providing direct current power for operating said first amplifier means; and means for delivering current from said second rectifier means to said first amplifier means.

Claim 10

The apparatus of claim 1 wherein said second amplifier means comprises: means for receiving and amplifying modulated signals provided by the microphone; continuously conductive modulator means, said modulator means at least in part defining said second amplifier means output stage, said modulator means including a semiconductor device which functions as a variable resistance; and means applying amplified microphone signals from said receiving and amplifying means to said modulator means.

Claim 11

The apparatus of claim 9 wherein said first amplifier means comprises: a differential amplifier.

Claim 12

In a telephone transceiver comprising a telephone handset including a microphone and a speaker, a subset supporting said handset, said subset also supporting a switch hook mechanism operated by said handset when resting on said subset, and an amplified loudspeaker and an amplified microphone, the improvement comprising: transformer means, said transformer means including a center-tapped primary winding and a secondary winding inductively coupled to said primary winding; means connecting the secondary winding of said transformer means to the loudspeaker, said connecting means including first amplifier means having a pair of input terminals connected to opposite ends of said transformer means secondary winding; means connecting a first end of said transformer means primary winding to a first terminal of a two wire telephone network; means including a balancing circuit for connecting the second end of said transformer means primary winding to the second terminal of the two wire telephone network; superimposed modulation amplifier means having an input circuit, said modulation amplifier means also having a pair of output terminals and an output stage which has the operating characteristics of a variable resistance, said output stage being connected across said output terminals and providing a modulated direct current output signal in response to a modulated input signal; means connecting the microphone to said modulation amplifier means input circuit whereby said modulating direct current output signal is commensurate with signals provided from the microphone; and means connecting said modulation amplifier means output terminals respectively to the second terminal of the telephone network and to the center-tap of said transformer means primary winding whereby said modulation amplifier means modulates the transformer means primary winding direct current to produce currents which are equal and in phase in both portions of said primary winding, the magnetic fields generated by said in-phase currents being substantially mutually cancelling so that there will be no current induced in the transformer secondary winding.

Claim 13

In a telephone transceiver comprising a telephone handset including a microphone and a speaker, a subset supporting said handset, said subset also supporting a switch hook mechanism operated by said handset when resting on said subset, and an amplified loudspeaker and an amplified microphone, the improvement comprising: transformer means, said transformer means including a center-tapped primary winding and a secondary winding inductively coupled to said primary winding; means connecting the secondary winding of said transformer means to the loudspeaker, said connecting means including first amplifier means having a pair of input terminals connected to opposite ends of said transformer means secondary winding; means connecting a first end of said transformer means primary winding to a first terminal of a two wire telephone network; means including a balancing circuit for connecting the second end of said transformer means primary winding to the second terminal of the two wire telephone network; superimposed modulation amplifier means having an input circuit, said modulation amplifier means also having a pair of output terminals and an output stage which has the operating characteristics of a variable resistance, said output stage being connected across said output terminals and providing a modulated direct current output signal in response to a modulated input signal; means connecting the microphone to said modulation amplifier means input circuit whereby said modulating direct current output signal is commensurate with signals provided from the microphone; and means connecting said modulation amplifier means output terminals respectively to the second terminal of the telephone network and to the center-tap of said transformer means primary winding whereby said modulation amplifier means modulates the transformer means primary winding direct current to produce currents which are equal and in phase in both portions of said primary winding, the magnetic fields generated by said in-phase currents being substantially mutually cancelling so that there will be no current induced in the transformer secondary winding.

Claim 14

The apparatus of claim 11 wherein said superimposed modulation amplifier means further comprises: first rectifier means, said first recitifier means having a first polarity output terminal connected to the second telephone network terminal by said first connecting means, said first rectifier means having a second polarity terminal connected to the center tap of said transformer means primary winding, said rectifier means first and second polarity terminals forming said superimposed modulation amplifier means output terminals, said first rectifier means deriving direct current power from the telephone line for operating said superimposed modulation amplifier; means for delivering direct current power derived from the telephone line by said first rectifier means to said superimposed modulation amplifier; and means for connecting said superimposed modulation amplifier output terminals to opposite polarity terminals of said first rectifier means whereby said superimposed modulation amplifier will modulate direct current flowing through said transformer means primary winding.

Claim 15

The apparatus of claim 12 further comprising: first switch means for selectively connecting the handset and amplified microphone and loudspeaker to the telephone network through said transformer means.

Claim 16

The apparatus of claim 13 wherein said first switch means comprises: a plurality of single pole double throw switches operated simultaneously, the normally closed terminals of said switches connecting said handset microphone and receiver respectively to said transformer primary and secondary windings, the normally open terminals of said switches connecting the output terminal of said modulation amplifier means and the input terminal of said first amplifier means respectively to said transformer means primary and secondary windings; and second switch means for connecting said modulation amplifier means output terminals and first amplifier means input terminals in parallel with said handset microphone and speaker with said plurality of switches in the normally closed condition.

Claim 17

The apparatus of claim 14 further comprising: a single housing having the microphone and loudspeaker and said amplifier and switch means mounted therein, said housing supporting the switch hook mechanism and the subset receiving the handset.