Telephone circuits utilizing active elements

Claim 2

A telephone circuit comprising a transistor circuit including an input terminal, an output terminal and a common terminal; receiving means having first and second terminals ; said first terminal being connected to said common terminal of said transistor circuit ; transmitting means including a first terminal connected to said input terminal of said transistor circuit and a second terminal connected to said second terminal of said receiving means ; telephone lines connected between said output terminal of said transistor means and the second terminal of said receiving means ; a balancing network connected between said input terminal and said common terminal of said transistor circuit ; a D.C. supply circuit connected between said telephone lines and said transmitting means for supplying current to said transmitting means ; a first variable impedance element connected in parallel with said transmitting means ; and a second variable impedance element connected in parallel with said receiving means ; said first and second variable impedance means varying their impedance in accordance with the D.C. voltage of said telephone lines.

Claim 3

The telephone circuit according to claim 1 wherein said transmitting means comprises an electromagnetic transmitter and a sending amplifier connected to said transmitter and supplied with a constant voltage.

Claim 4

The telephone circuit according to claim 1 wherein said D.C. supply circuit comprises a constant current circuit connected in parallel with said telephonE lines, and biasing means for biasing said constant current circuit to obtain a constant voltage.

Claim 5

The telephone circuit according to claim 3 wherein said biasing means includes at least one constant voltage diode.

Claim 6

The telephone circuit according to claim 1 wherein said first variable impedance element comprises a field effect transistor having a drain terminal and a source terminal which are connected across said electromagnetic transmitter and a gate terminal connected to means sensitive to the D.C. voltage of said telephone lines.

Claim 7

The telephone circuit according to claim 5 wherein said means sensitive to said D.C. voltage comprises a resistance potentiometer connected across said telephone lines.

Claim 8

The telephone circuit according to claim 1 wherein said second variable impedance element comprises a field effect transistor having a drain terminal and a source terminal connected across said receiving means and a gate terminal connected to means sensitive to the D.C. voltage of said telephone lines.

Claim 9

A telephone circuit comprising a potentiometer having an output tap and connected across telephone lines ; a D.C. supply circuit connnected in parallel with said potentiometer and including a constant current circuit and biasing means for biasing said constant current circuit for providing a constant voltage ; a transistor including an output terminal, an input terminal and a common terminal ; said output terminal being connected to one of said telephone lines ; receiving means with one terminal connected to said common terminal of said transistor and the other terminal connected to the other of said telephone lines ; a balancing network with one terminal connected to said input terminal of said transistor and the other terminal to said common terminal of said transistor ; transmitting means including a sending amplifier having an output terminal connected to said input terminal of said transistor and constant voltage input terminals energized by a said constant voltage, and a transmitter having two terminals connected to another input terminals of said sending amplifier; a first field effect transistor having a drain terminal and a source terminal which are connected in parallel with said transmitter ; and a second field effect transistor having a drain terminal connected to the one end of said receiving means and a gate terminal connected to the gate terminal of said first field effect transistor ; said output tap of said potentiometer being connected to the gate terminals of said first and second field effect transistors ; said biasing means of said D.C. supply circuit being connected to said constant voltage input terminals of said sending amplifier ; and an intermediate point of said biasing means being connected to the source terminals of said first and second field effect transistors.

Claim 10

A telephone circuit comprising a potentiometer having an output tap and connected across telephone lines ; a D.C. supply circuit connnected in parallel with said potentiometer and including a constant current circuit and biasing means for biasing said constant current circuit for providing a constant voltage ; a transistor including an output terminal, an input terminal and a common terminal ; said output terminal being connected to one of said telephone lines ; receiving means with one terminal connected to said common terminal of said transistor and the other terminal connected to the other of said telephone lines ; a balancing network with one terminal connected to said input terminal of said transistor and the other terminal to said common terminal of said transistor ; transmitting means including a sending amplifier having an output terminal connected to said input terminal of said transistor and constant voltage input terminals energized by a said constant voltage, and a transmitter having two terminals connected to another input terminals of said sending amplifier; a first field effect transistor having a drain terminal and a source terminal which are connected in parallel with said transmitter ; and a second field effect transistor having a drain terminal connected to the one end of said receiving means and a gate terminal connected to the gate terminal of said first field effect transistor ; said output tap of said potentiometer being connected to the gate terminals of said first and second field effect transistors ; said biasing means of said D.C. supply circuit being connected to said constant voltage input terminals of said sending amplifier ; and an intermediate point of said biasing means being connected to the source terminals of said first and second field effect transistors.

Claim 11

The telephone circuit according to claim 8 wherein said biasing means of said D.C. supply means comprises two serially connected constant voltage diodes and the juncture between said diodes comprises said intermediate point.

Claim 12

The telephone circuit according to claim 8 wherein said biasing means of said D.C. supply circuit comprises a single constant voltage diode and a potentiometer connected in parallel with said constant voltage diode, an intermediate tap of said potentiometer being utilized as said intermediate point.

Claim 13

The telephone circuit according to claim 8 wherein said balancing network comprises a parallel combination of a capacitor and a resistor, and a resistor connected in series with said parallel combination and wherein said balancing network is connected between said input terminal and said common terminal of said transistor through a capacitor which provides a low impedance path for A.C. components.

Claim 14

The telephone circuit according to claim 11 wherein said transistor, resistors, and field effect transistors are fabricated as an integrated circuit on a substrate.