Telephone subset circuit

Claim 2

An electronic circuit for use in a telephone subscriber''s instrument having a microphone and a receiving transducer comprising: first amplification means for coupling said microphone to a twowire telephone line coupled to a telephone exchange and to provide a side tone; automatic gain control means coupled to said microphone and said first amplification means; second amplification means for coupling said line to said receiving transducer; voltage regulator means coupled to said line and said first and second amplification means, said voltage regulator means being responsive to line conditions of said line to adjust the gain of both of said first and second amplification means according to said line conditions; a first conductor coupled between said first amplification means and said second amplification means to provide said side tone for said receiving transducer to enable a subscriber to hear in said receiving transducer what is leaving said instrument; a second conductor to couple an output of said first amplification means to one wire of said line; and a resistor-capacitor filter network coupled between one wire of said line and the input of said second amplification means, said filter network conducting therethrough an equal value of output signal from said first amplification means in phase opposition thereby leaving only said side tone and an input signal from said telephone line to be coupled to said second amplification means.

Claim 3

An electronic circuit according to claim 1, wherein said first and second amplification means, said automatic gain control means and said voltage regulator means are integrated circuitry formed on a single semiconductor chip.

Claim 4

An electronic circuit according to claim 2, wherein said first and second amplification means, said automatic gain control means, said voltage regulator means and said filter network include only transistors, semiconductor diodes, resistors and capacitors.

Claim 5

An electronic circuit according to claim 2, wherein said line is coupled to said chip by a pair of terminals formed in said chip.

Claim 6

An electronic circuit according to claim 4, wherein said filter network is disposed externally of said chip connected to one of said pair of terminals and connected to an additional terminal formed in said chip, said additional terminal being connected to the output of said first amplification means and the input of said second amplification means.

Claim 7

An electronic circuit for use in a telephone subscriber''s instrument having a microphone and a receiving transducer comprising: a first pair of terminals to which a two-wire telephone line is connected when said electronic circuit is in use and over which power for said electronic circuit is supplied; a second pair of terminals to which said microphone is connected when said electronic circuit is in use; automatic gain control means coupled to said second pair of terminals to receive speech from said microphone; first amplification means coupled to said gain control means and providing a side tone; a voltage regulator connected to said first pair of terminals responsive to the level of current on said line when said electronic circuit is in use, said voltage regulator having a first output connection and a second output connection; said first output connection coupling said regulator to said first amplification means to enable the gain of said first amplification means to be adjusted in accordance with the level of said line current; a first output from said first amplification means coupled to one of said first pair of terminals and hence to said line when said electronic circuit is in use; a third pair of terminals to which said receiving transducer is connected when said electronic circuit is in use; second amplification means having its input connected to said one of said first pair of terminals and its output connected to said third pair of terminals when said electronic circuit is in use; said second and third pair of terminals being isolated from each other by said first and second amplification means; said second output connection coupling said regulator to said second amplification means to enable to gain of said second amplification means to be adjusted in accordance with the level of said line current; and a second output from said first amplification means coupled to said second amplification means to couple said side tone to said second amplification means and hence to said receiving transducer to enable a subscriber to hear in said receiving transducer what is leaving said instrument.

Claim 8

An electronic circuit for use in a telephone subscriber''s instrument having a microphone and a receiving transducer comprising: a first pair of terminals to which a two-wire telephone line is connected when said electronic circuit is in use and over which power for said electronic circuit is supplied; a second pair of terminals to which said microphone is connected when said electronic circuit is in use; automatic gain control means coupled to said second pair of terminals to receive speech from said microphone; first amplification means coupled to said gain control means and providing a side tone; a voltage regulator connected to said first pair of terminals responsive to the level of current on said line when said electronic circuit is in use, said voltage regulator having a first output connection and a second output connection; said first output connection coupling said regulator to said first amplification means to enable the gain of said first amplification means to be adjusted in accordance with the level of said line current; a first output from said first amplification means coupled to one of said first pair of terminals and hence to said line when said electronic circuit is in use; a third pair of terminals to which said receiving transducer is connected when said electronic circuit is in use; second amplification means having its input connected to said one of said first pair of terminals and its output connected to said third pair of terminals when said electronic circuit is in use; said second and third pair of terminals being isolated from each other by said first and second amplification means; said second output connection coupling said regulator to said second amplification means to enable to gain of said second amplification means to be adjusted in accordance with the level of said line current; and a second output from said first amplification means coupled to said second amplification means to couple said side tone to said second amplification means and hence to said receiving transducer to enable a subscriber to hear in said receiving transducer what is leaving said instrument.

Claim 9

An electronic circuit according to claim 6, wherein said automatic gain control means, said first and second amplification means, said voltage regulator, said first and second connections and said first and second outputs are integrated circuitry formed on a single semiconductor chip, and said first, second and third pair of terminals are formed in said chip.

Claim 10

An electronic circuit according to claim 7, wherein said automatic gain control means, said first and second amplification means and said voltage regulator include only transistors, semiconductor diodes, resistors and capacitors.

Claim 11

An electronic circuit according to claim 6, further including a resistor-capacitor filter network connected between said one of said first pair of terminals and said second output of said first amplification means, said filter network having an equal value of output signal from said first amplification means in phase opposition therein and an input signal from said telephone line to said second amplification means therein thereby leaving only said side tone and said input signal for coupling to said second amplification means.

Claim 12

An electronic circuit according to claim 9, wherein said automatic gain control means, said first and second amplification means, said voltage regulator and said first and second outputs are integrated circuitry formed on a single semiconductor chip, and said first, second and third pair of terminals are formed in said chip, said resistor-capacItor filter network, said microphone and said receiving transducer being disposed externally of said chip.

Claim 13

An electronic circuit according to claim 9, further including a gain control detection means coupled to said automatic gain control means and said first amplification means controlled by both said automatic gain control means and said first amplification means to enhance gain control of said first amplification means when speech level exceeds a specified value.

Claim 14

An electronic circuit according to claim 11, wherein said first amplification means is a chain of three amplifiers with said gain control being exerted on the second amplifier of said chain.

Claim 15

An electronic circuit according to claim 11, wherein said automatic gain control means, said first and second amplification means, said voltage regulator, said first and second outputs and said gain control detection means are integrated circuitry formed on a single semiconductor chip, and said first, second and third pair of terminals are formed in said chip, said resistor-capacitor filter network, said microphone and said receiving transducer being disposed externally of said chip.

Claim 16

An electronic circuit according to claim 13, wherein said automatic gain control means, said first and second amplification means, said voltage regulator and said gain control detection means include only transistors, semiconductor diodes, resistors and capacitors.

Claim 17

An electronic circuit according to claim 6, further including a gain control detection means coupled to said automatic gain control means and said first amplification means controlled by both said automatic gain control means and said first amplification means to enhance gain control of said first amplification means when speech level exceeds a specified value.

Claim 18

An electronic circuit according to claim 15, wherein said first amplification means is a chain of three amplifiers with said gain control being exerted on the second amplifier of said chain.

Claim 19

An electronic circuit according to claim 15, wherein said automatic gain control means, said first and second amplification means, said voltage regulator, said first and second outputs and said gain control detection means are integrated circuitry formed on a single semiconductor chip, and said first, second and third pair of terminals are formed in said chip, said microphone and said receiving transducer being disposed externally of said chip.

Claim 20

An electronic circuit according to claim 17, wherein said automatic gain control means, said first and second amplification means, said voltage regulator and said gain control detection means include only transistors, semiconductor diodes, resistors and capacitors.