Telecommunication line circuit

Claim 2

Telecommunication line circuit including a Herter bridge (RO - R5) with a first pair of terminals (STB, SRA) coupled to a bidirectinal 2-wire line, a second pair of terminals (STA, SRB) coupled to an exchange; and a third pair of terminals (A, B) where longitudinal currents are eliminated from sensed signals, as well as a ringing generator (RC) that may be coupled across the second pair of terminals, characterized in that the second pair of terminals is coupled to a receive leg (Rx) of a 4-wire exchange circuit and, through switching means (sw30/31), to the ringing generator while the third pair of terminals is coupled to a transmit leg (Tx) of the 4-wire exchange circuit.

Claim 3

Telecommunication line circuit according to claim 1, characterized in that the third pair of terminals (A, B) of the Herter bridge (R0 - R5) is also coupled to AC/DC feedback circuits (C1, OA3; DCFC) enabling to synthesize desired characteristics and values of AC impedance and DC resistances from series feed resistances (R0, Rl) forming part of the Herter bridge as well as of the AC/DC feedback circuits.

Claim 4

Telecommunication line circuit according to claim 2 characterized in that the Herter bridge (RO - R5) is designed so that the output at the third pair of terminals (A, B) contains only components proportional to voltages across the series feed resistances (R0, R1).

Claim 5

Telecommunication line circuit according to claim 1, characterized in that the terminals (A, B) of said third pair are coupled to respective inputs of an operational amplifier (OA2) as well as to a first bias source (VAUX) through respective first bias resistances CR6, R7) of equal value, so as to ensure that an input stage of said operational amplifier (OA2) is not driven outside its operation range upon a ringing signal being applied across said second pair of terminals (STA, SRB) by said ringing generator (RC).

Claim 6

Telecommunication line circuit according to claim 4, characterized in that the non-inverting input of said operational amplifier (OA2) is connected to a second bias source (VAG) through a second bias resistance (R9), whilst its output (C01) is connected to its inverting input through a feedback third resistance (R8), the values of the resistances of said Herter bridge (RO - R5) and of said second (R9) and third (R8) resistance being so chosen that the output stage of said operational amplifier (OA2) is not driven outside its operating range upon said ringing signal being applied across said second pair of terminals (STA, SRB).

Claim 7

Telecommunication line circuit according to claim 5, characterized in that the value of said second bias source (VAG) constitutes the reference output of said operational amplifier (OA2) in the absence of a sensed signal and that the value of said first bias source (VAUX) and of said first (R6, R7) second (R9) resistances have been so chosen 3VAUX - VAG that from a predetermined wanted value ( ) 2 onwards more current flows from said non-inverting input (B) towards said first bias source (VAUX) than towards said second bias source (VAG).

Claim 8

Telecommunication line according to claim 4, characterized in that the output (C01) of said operational amplifier (OA2) is coupled to a DC level detection circuit (CO) through a signal path (R23, PG3, C3, PG4, PG2) which includes a filter circuit (R23, C2) for said ringing signal and which is unblocked (RNG=l) upon said ringing signal being applied across said second pair of terminals (STA, SRB).

Claim 9

Telecommunication line circuit according to claim 7, characterized in that the output (COl) of said operational amplifier (OA2) is also coupled to said DC level detection circuit (CO) through a second signal path (FC, OA6, PG1), which is unblocked (RNG=O) when no ringing signal is applied across said second pair of terminals (STA, SRB).

Claim 10

Telecommunication line circuit according to claim 4, characterized in that said receive leg is coupled to respective first push-pull inputs (TDC, RAC) of two operational line amplifiers (LOA0, LOA1) whose outputs are coupled to respective ones of said second pair of terminals (STA, SRB) and that the output of said operational amplifier (OA2) is capacitively (Cl) coupled to respective second push-pull inputs (TAC, RDC) of said two operational line amplifiers, all in such a way that an AC impedance synthesis circuit is formed.

Claim 11

Telecommunication line circuit according to claim 9, characterized in that the output (C01) of said operational amplifier (OA2) is capacitively (CI) coupled to said second push-pull inputs (TAC, RDC) through an amplifier stage (OA3) including an impedance network determining the desired AC impedance to be synthesized.

Claim 12

Telecommunication line circuit according to claim 10 characterized in that the output of said operational amplifier stage 3 (OA3) is coupled (C2, R21, R22) to said transmit leg (Tx).

Claim 13

Telecommunication line circuit according to claim 9, characterized in that the output (C01) of said operational amplifier (OA2) is coupled (DCFC) to voltage supply inputs (VEET) of said two operational line amplifiers (LOA0, LOA1) in such a way that a resistance synthesis circuit is formed.

Claim 14

Telecommunication line circuit according to claim 1, characterized in that it includes second switching means (sw10/11) to disconnect said second pair of terminals (STA, SRB) from said receive leg (Rx) when said first mentioned switching means (sw30/31) connect said ringing generator (RC) to said second pair of terminals and vice-versa.

Claim 15

Telecommunication line circuit (SLIC) including a pair of operational line amplifiers (LOAO, LOA1) able to supply DC feed signals as well as AC signals, e.g. speech, received on a receive leg (Rx) to a telecommunication station (TSS) through respective feed resistances (R0, Rl) and respective line conductors of a telecommunication line, said station (TSS) being able to generate AC signals, e.g. speech, and to open or close a DC loop between said line conductors (LIO, LII) a sensing circuit (RO, Rl, SENC) including said feed resistance (RD, Rl) and able to sense signals on said feed resistances and to generate on its output (CO1) a sensed output signal which is capacitively coupled (Cl) to said line amplifiers (LOAO, LOA1) and also coupled to a transmission leg (Tx) and to a DC level detection circuit (CO), said operational amplifiers and said sensing circuit forming an impedance synthesis circuit, characterized in that it also includes a ringing generator (RC) able to supply ringing signals to said line and to said sensing circuit (R0, R1. SENC) which is also able to sense ringing signals.

Claim 16

Telecommunication line circuit (SLIC) including a pair of operational line amplifiers (LOAO, LOA1) able to supply DC feed signals as well as AC signals, e.g. speech, received on a receive leg (Rx) to a telecommunication station (TSS) through respective feed resistances (R0, Rl) and respective line conductors of a telecommunication line, said station (TSS) being able to generate AC signals, e.g. speech, and to open or close a DC loop between said line conductors (LIO, LII) a sensing circuit (RO, Rl, SENC) including said feed resistance (RD, Rl) and able to sense signals on said feed resistances and to generate on its output (CO1) a sensed output signal which is capacitively coupled (Cl) to said line amplifiers (LOAO, LOA1) and also coupled to a transmission leg (Tx) and to a DC level detection circuit (CO), said operational amplifiers and said sensing circuit forming an impedance synthesis circuit, characterized in that it also includes a ringing generator (RC) able to supply ringing signals to said line and to said sensing circuit (R0, R1. SENC) which is also able to sense ringing signals.

Claim 17

Telecommunication line circuit according to claim 14, characterized in that said sensing circuit includes a Herter bridge.