Electronic telephone network

Claim 2

An electronic telephone network for receiving and transmitting signals over a two-wire telephone line the impedance of which may vary over a given range, said network comprising in combination: a preamplifier, means for applying telephone input signals to said preamplifier; a line-driver amplifier having an input coupled to said preamplifier and an output coupled to said line and being responsive to said preamplifier for amplifying the output signals of said preamplifier and wherein the gain of said line-driver amplifier varies in accordance with its output impedance relative to the impedance of said line; means coupled across said line-driver amplifier for substantially separating received signals from said telephone line and for providing the separated signals at an output thereof, said separating means including an attenuator wherein an attenuated portion of the signals at said output of said line-driver amplifier is combined with a portion of the signals at its input to provide said separated signals; a receive amplifier coupled to said output of said separating means for increasing the level of said separated signals; means for deriving operating potential for said network from said line; means coupled between said preamplifier and said line-driver amplifier and responsive to said telephone input signals for providing a control signal when the level of said telephone input signals exceeds a predetermined value; and, means coupled to said line-driver amplifier and responsive to said control signal for decreasing the AC output impedance of said line-driver amplifier from a first given level to a second given level when the level of said telephone input signals exceeds said predetermined value, thereby to reduce the gain variations of said line-driver amplifier with respect to variations in the impedance of said line over said given range.

Claim 3

An electronic telephone network for receiving and transmitting telephone signals over a two-wire line said network comprising in combination: a first amplifier; means for applying the transmit portion of said telephone signals to said first amplifier; means for providing a control signal when the transmit portion of said telephone signals exceeds a predetermined level; first means responsive to said first amplifier and said control signal for applying the output signal of said first amplifier to said line, said first means comprising a line-driver amplifier having at least one output transistor having first and second main electrodes coupled across said line and a control electrode, said line-driver amplifier including means for controlling the value of the DC current flowing through said main electrodes and said line to a predetermined value, and said line-driver amplifier including means responsive to said control signal for decreasing the AC output impedance of said line-driver amplifier when the transmit portion of said telephone signals exceeds said predetermined level; second means responsive to said first amplifier and the output of said first means for separating the received telephone signals from the composite telephone signals and for providing the separated signals at an output thereof, said separating means including an attenuator coupled across said line-driver amplifier wherein the output of said first amplifier is combined with an attenuated version of the output of said line-driver amplifier to provide said separated signals; a second amplifier coupled to said output of said second means for increasing the level of said separated signals; third means cooperating with said line-driver amplifier for deriving operating potential for said network from said line; and, fourth means coupled between said first amplifier and said first means and responsive to a signal related to said operating potential for altering the amplitude characteristics of said output signal of said first amplifier in accordance with the loss characteristics of said line.

Claim 4

An electronic telephone network for receiving and transmitting telephone signals over a two-wire line said network comprising in combination: a first amplifier; means for applying the transmit portion of said telephone signals to said first amplifier; means for providing a control signal when the transmit portion of said telephone signals exceeds a predetermined level; first means responsive to said first amplifier and said control signal for applying the output signal of said first amplifier to said line, said first means comprising a line-driver amplifier having at least one output transistor having first and second main electrodes coupled across said line and a control electrode, said line-driver amplifier including means for controlling the value of the DC current flowing through said main electrodes and said line to a predetermined value, and said line-driver amplifier including means responsive to said control signal for decreasing the AC output impedance of said line-driver amplifier when the transmit portion of said telephone signals exceeds said predetermined level; second means responsive to said first amplifier and the output of said first means for separating the received telephone signals from the composite telephone signals and for providing the separated signals at an output thereof, said separating means including an attenuator coupled across said line-driver amplifier wherein the output of said first amplifier is combined with an attenuated version of the output of said line-driver amplifier to provide said separated signals; a second amplifier coupled to said output of said second means for increasing the level of said separated signals; third means cooperating with said line-driver amplifier for deriving operating potential for said network from said line; and, fourth means coupled between said first amplifier and said first means and responsive to a signal related to said operating potential for altering the amplitude characteristics of said output signal of said first amplifier in accordance with the loss characteristics of said line.

Claim 5

The telephone network according to claim 2, including a switchable attenuator coupled between said first amplifier and said line-driver amplifier and responsive to said control signal for attenuating the output signal from said first amplifier when the transmit portion of said input telephone signals are less than said predetermined level.

Claim 6

The telephone network according to claim 3, wherein said first and second amplifiers are operatively coupled to said operating potential through constant current loads.

Claim 7

An amplifier adapted for coupling telephone signals to a telephone line and for controlling the DC current flowing through said telephone line to a predetermined value at a given telephone line loop resistance, said amplifier comprising: at least one output transistor having first and second main electrodes coupled across said telephone line, and having a control electrode; means for applying said telephone signals to said control electrode; means coupled between said control electrode and one of said main electrodes for deriving a first signal related to the DC current flowing through said main electrodes; means coupled across said telephone line for deriving a second signal related to the DC voltage appearing across said telephone line; means for comparing said first and second signals to provide a third signal indicative of the difference between said first and second signals; and means coupled between said control electrode and the comparing means, and responsive to said third signal for adjusting the value of said DC current flowing through said main electrodes to said predetermined value.

Claim 8

An amplifier adapted for coupling telephone signals to a telephone line and for controlling the DC current flowing through said telephone line to a predetermined value at a given telephone line loop resistance, said amplifier comprising: at least one output transistor having first and second main electrodes coupled across said telephone line, and having a control electrode; means for applying said telephone signals to said control electrode; means coupled between said control electrode and one of said main electrodes for deriving a first signal related to the DC current flowing through said main electrodes; means coupled across said telephone line for deriving a second signal related to the DC voltage appearing across said telephone line; means for comparing said first and second signals to provide a third signal indicative of the difference between said first and second signals; and means coupled between said control electrode and the comparing means, and responsive to said third signal for adjusting the value of said DC current flowing through said main electrodes to said predetermined value.

Claim 9

The amplifier according to claim 5, wherein said main electrodes comprise a collector and an emitter electrode, wherein said control electrode comprises a base electrode and wherein said means for deriving said first signal is coupled between said base and emitter electrodes.

Claim 10

The amplifier according to claim 6, wherein said first signal is proportional to the DC current flowing through said telephone line.

Claim 11

The amplifier according to claim 7, wherein said first signal is the base-emitter DC voltage of said transistor.

Claim 12

The amplifier according to claim 5, wherein a plurality of transistors, having their respective electrodes parallel connected, are provided.

Claim 13

The amplifier according to claim 9, wherein said transistors have substantially matched DC operating characteristics.

Claim 14

The amplifier according to claim 5, wherein said means for comparing said first and second signals comprises a balanced differential input amplifier including a first, second and third transistors, said first transistor providing an active constant current source for said second and third transistors, said second and third transistors having input electrodes respectively coupled to one of said first and second signals, and one of said first and second transistors having its output electrode coupled to said control electrode of said output transistor.

Claim 15

The amplifier according to claim 5, wherein said means for applying said telephone signals incorporates said means for comparing said first and second signals.

Claim 16

An amplifier adapted for coupling telephone signals to a telephone line while controlling the DC line current flowing through said telephone line to a predetermined value at a given telephone line loop resistance, said amplifier comprising: at least one output transistor having first and second main electrodes coupled across said telephone line, and having a control electrode; means for applying said telephone signals to said control electrode; first means coupled between said control electrode and one of said main electrodes for deriving a first signal related to the DC line current flowing through said main electrodes; second means for providing a reference signal related to said given telephone line loop resistance; and means coupled to said first and second means and to said control electrode, and responsive to said first signal and said reference signal for adjusting said DC line current to said predetermined value.

Claim 17

An amplifier adapted for coupling telephone signals to a telephone line while controlling the DC line current flowing through said telephone line to a predetermined value at a given telephone line loop resistance, said amplifier comprising: at least one output transistor having first and second main electrodes coupled across said telephone line, and having a control electrode; means for applying said telephone signals to said control electrode; first means coupled between said control electrode and one of said main electrodes for deriving a first signal related to the DC line current flowing through said main electrodes; second means for providing a reference signal related to said given telephone line loop resistance; and means coupled to said first and second means and to said control electrode, and responsive to said first signal and said reference signal for adjusting said DC line current to said predetermined value.

Claim 18

The amplifier according to claim 13, wherein said first signal is derived from the base-emitter voltage of said output transistor.

Claim 19

The amplifier according to claim 14, wherein said reference signal is provided by a voltage divider coupled across said telephone line.

Claim 20

The amplifier according to claim 13, wherein said output transistor is modulated by said telephone signals over a range of conductivity values including its cut-off and saturated values.

Claim 21

The amplifier according to claim 13, wherein said output transistor includes a feedback loop between one of said main electrodes and said control electrode, said feedback loop including means responsive to said telephone signals for translating the AC output impedance of said amplifier between two levels wherein said output impedance is decreased when said amplifier is applying said telephone signals to said telephone line.