EP0116767A2 — Battery feed circuit for a telephone subscriber l…

Claim 1

Independent Claim 88 words

A battery feed circuit, for supplying direct current (DC) to a two wire subscriber line loop including a telephone set, comprising: DC impedance active convertor means operable to provide a variable DC output voltage, with a specified value of DC impedance, to the subscriber line ; and switching power supply means operable to provide a variable DC voltage to a power source terminal of the DC impedance active convertor means in dependence upon the length of the subscriber line and state (on-hook or off-hook) of the telephone set.

Claim 2

Dependent Claim 88 words

A battery feed circuit, for supplying direct current (DC) to a two wire subscriber line loop including a telephone set, comprising: DC impedance active convertor means operable to provide a variable DC output voltage, with a specified value of DC impedance, to the subscriber line ; and switching power supply means operable to provide a variable DC voltage to a power source terminal of the DC impedance active convertor means in dependence upon the length of the subscriber line and state (on-hook or off-hook) of the telephone set.

Claim 3

Dependent Claim 62 words

A circuit as claimed in claim 1, wherein the DC impedance active convertor means comprises an operational amplifier connected in series with one of the two wires of the subscriber line, and a DC voltage feedback loop the input of which is connected to the said one of the two wires and the output of which is connected to the operational amplifier.

Claim 4

Dependent Claim 58 words

A circuit as claimed in claim 1 or 2, wherein the switching power supply means are operable to compare a power source voltage for the said operational amplifier with the output voltage of the DC voltage feedback loop, and to control the said power source voltage to be less than the output voltage of the DC feedback loop.

Claim 5

Dependent Claim 157 words

A battery feed circuit, for supplying DC current to a two wire subscriber line, comprising: first and second amplifiers, respectively connected to first and second wires of the subscriber line, operable to provide the first wire and the second wire with DC voltage; first and second output resistors, respectively connected to the outputs of the first and second amplifiers, providing those amplifiers with respective output impedances; a DC voltage feedback loop, having an input connected to at least the said first wire, operable to provide a DC output voltage proportional to the DC voltage on the said first wire and to feed that output voltage back to the first amplifier; and a switching power supply operable to compare a power source voltage of the first amplifier with the output voltage of the DC voltage feedback loop, and to control the said power source voltage to be less than the output voltage of the DC voltage feedback loop.

Claim 6

Dependent Claim 157 words

A battery feed circuit, for supplying DC current to a two wire subscriber line, comprising: first and second amplifiers, respectively connected to first and second wires of the subscriber line, operable to provide the first wire and the second wire with DC voltage; first and second output resistors, respectively connected to the outputs of the first and second amplifiers, providing those amplifiers with respective output impedances; a DC voltage feedback loop, having an input connected to at least the said first wire, operable to provide a DC output voltage proportional to the DC voltage on the said first wire and to feed that output voltage back to the first amplifier; and a switching power supply operable to compare a power source voltage of the first amplifier with the output voltage of the DC voltage feedback loop, and to control the said power source voltage to be less than the output voltage of the DC voltage feedback loop.

Claim 7

Dependent Claim 41 words

A battery feed circuit as claimed in claim 4, further comprising an AC feedback loop, operable differentially to amplify AC components of signals coming from the first and second wires, and to provide feedback to the first and second amplifiers respectively.

Claim 8

Dependent Claim 225 words

A circuit as claimed in claim 4 or 5, wherein the switching power supply comprises: a zener diode,connected between a power source voltage input terminal of the first amplifier and an output terminal of the DC voltage feedback loop, operable to provide a DC reference voltage ; a reference wave signal generator, generating a reference wave signal; first comparator means , operable to compare the voltage of the said power source voltage input terminal of the first amplifier with the DC reference voltage, and to provide high voltage output or a low voltage output in dependence upon which of the compared voltages is higher; second comparator means, operable to compare said high voltage or said low voltage, output from the first comparator means, with the reference wave signal, and to provide a rectangular wave signal, the waveform of which depends upon the results of such comparison; and switching transistor circuit means, comprising a transistor, a capacitor, and first and second resistors, operable to provide a DC voltage by on/off switching of the collector current of the transistor in accordance with the rectangular wave signal, supplied through the first resistor to the transistor, the capacitor having a discharge path through the second resistor and the transistor, when the transistor is on, and a charge path including the first and second amplifiers when the transistor is off.

Claim 9

Dependent Claim 36 words

A battery feed circuit as claimed in claim 4,5 or 6, wherein each of the first and second amplifiers is a non-polarity inverting operational amplifier, having unity voltage gain, infinite input impedance, and zero output impedance.

Claim 10

Dependent Claim 40 words

A battery feed circuit as claimed in claim 4,5,6 or 7, wherein each of the first and second output resistors is the smallest possible consistent with AC signal phase difference between input and output of the resistor being negligibly small.

Claim 11

Dependent Claim 33 words

A battery feed circuit as claimed in claim 4,5,6, 7 or 8, wherein the input of the second amplifier is biased by a small value of DC bias voltage, for example 3 volts.

Claim 12

Dependent Claim 28 words

A battery feed circuit as claimed in any one of claims 4 to 9, wherein the zener voltage of the zener diode is small, for example 3 volts.

Claim 13

Dependent Claim 44 words

A battery feed circuit as claimed in claim 6, or any one of claims 7 to 10 read as appended to claim 6, wherein the second resistor of the switching transistor means is smaller than the internal DC resistance of the said charging path.

Claim 14

Dependent Claim 25 words

A battery feed circuit as claimed in any one of claims 4 to 11, wherein the reference wave signal has a triangular or sawtooth waveform.

Claim 15

Dependent Claim 36 words

A battery feed circuit as claimed in any of claims 4 to 12, wherein the frequency of the reference wave signal is a multiple of a sampling frequency used for PCM coding of a telephone signal.

Claim 16

Dependent Claim 64 words

A battery feed circuit as claimed in claim 6, or any one of claims 7 to 13 read as appended to claim 6, wherein the frequency of the reference wave signal is selected so that the value of the capacitor of the switching transistor circuit means is as small as possible consistent with constrained limits on the time constant of the said charging path.

Battery feed circuit for a telephone subscriber line

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