US 5,398,282 AGranted

Automatic sidetone selector

AssigneeNorthern Telecom Limited

InventorsChristopher M. Forrester, David A. Pepper, Guy J. Fortier, Norbert J. Diesing, W. J. Leonard McCready

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Abstract

Sidetone in a four-wire telephone station set that is coupled to a two-wire telephone line through a four-to-two wire hybrid circuit is automatically and cancel the phase "to a predetermined value", set by incrementally adjusting a balancing impedance connected to the circuit until an optimum impedance match between the telephone set and line is achieved. Under software control, during idle intervals between dialed digits when a call is initiated, a microcontroller mutes the telephone transmitter and receiver on the telephone side of the circuit and substitutes for these components a tone signal generator to produce a sidetone signal that is applied to a full-wave rectifier and therefrom to a peak voltage detector to generate a sidetone envelope. Individual ones of several impedance balancing networks are then sequentially connected to the telephone side of the circuit and the sidetone envelope for each balancing impedance is digitally encoded and stored. A mutual comparison of the stored data indicates a minimum sidetone value which corresponds to an optimum impedance match that is retained unless a subsequent telephone call results in a change of balancing impedance.

Claims22

Dependent claims

Apparatus for automatically adjusting sidetone to an optimum value in a first telephone station set including a keypad for dialing digits, a transmitter and a receiver switchably connectable via respective signal paths to a telephone side of a hybrid balance circuit having a line side connected to a telephone central office, comprising in combination:

means for muting the transmitter and receiver;
means for detecting the presence of any dial tone and noise signals in the muted receiver signal path;
means for injecting a tone signal into the transmitter signal path in the absence of any dial tone and noise signals or when any such detected signals are less than a predetermined threshold value;
impedance means operably connectable to the telephone side of the balance circuit in incrementally adjustable steps for matching a telephone line connecting the line side of the balance circuit to the central office;
means for generating an envelope of the tone signal in the receiver signal path corresponding to a sidetone value for each incremental impedance adjustment;
means for storing the respective envelopes of the tone signals as data in volatile memory means and comparing each stored envelope with a predetermined reference value;
and
means responsive to a best match between the compared envelopes and reference value for selectively connecting the correspondingly adjusted impedance across the telephone side of the balance circuit, thereby matching the telephone line and setting the sidetone to the optimum value.

5 more elements

A method for automatically adjusting sidetone to an optimum value in a telephone station set including a keypad for dialing digits, a transmitter and a receiver switchably connectable via respective signal paths to a telephone side of a hybrid balance circuit having a line side connected to a telephone central office, comprising the steps of:

muting the transmitter and receiver;
detecting the presence of any dial tone and noise signals in the muted receiver signal path;
injecting a tone signal into the transmitter signal path in the absence of any dial tone and noise signals or when any such detected signals are less than a predetermined threshold value;
operably connecting impedance means to the telephone side of the balance circuit in incrementally adjustable steps for matching a telephone line connecting the line side of the balance circuit to the central office;
generating an envelope of the tone signal in the receiver signal path corresponding to a sidetone value for each incremental impedance adjustment;
storing the respective envelopes of the tone signals as data in volatile memory means and comparing each stored envelope with a predetermined reference value;
and
connecting across the telephone side of the balance circuit the adjusted impedance that corresponds to a best match detected between the compared envelopes and reference value, thereby matching the telephone line and setting the sidetone to the optimum value.

5 more elements

Dependencies are inferred from the claim text.