Method and device for the matching of the impedances of the subscriber termination and of the subscriber access to the characteristic impedance of the subscriber telephone line

Claim 2

Device for the adjustment of the subscriber access impedance (Zau) as well as that of the subscriber termination (Ztu) to the characteristic impedance (Zc) of the telephone line (LT) connecting the subscriber termination (TU) to the subscriber access (AU), in this subscriber termination there is initially an impedance (Zau) and (Ztu) different from the characteristic impedance (Zc) of the subscriber telephone line, characterized in that it includes in the subscriber access (AU) and in the subscriber termination (TU), respectively: - a second generator (Txau and Txtu, respectively) of periodical reference signals (Eau and Etu, respectively) connected to the end (C and A, respectively) of said matching impedance (Zau and Ztu, respectively) opposed to that in the direction of the subscriber telephone line (LT); - second multiplier means (M2 and M1, respectively) connected to said generator (Txau and Txtu, respectively) and to a constant coefficient (C); - second adder means (Σ2 and Σ1, respectively) having one input connected to said output of said multiplier means (M2 and M1, respectively) and the other input connected to the end (D and B, respectively) of the adjustment impedance (Zau and Ztu, respectively) directed towards the subscriber telephone line (LT), suitable to produce an error signal (ERau and ERtu, respectively); - a phase error detector (XO2 and X01, respectively) having the inputs connected to the heads of said impedance to be adjusted (Zau and Ztu, respectively) through the same number of comparator circuits (CP3, CP4 and CP1, CP2), respectively, two of them (CP1, CP3) being connected in differential mode; - a control logic (LCau and LCtu, respectively) for the timed and programmed control of the above mentioned components having the inputs connected to the output of the phase error detector (XO2 and XO1, respectively), to the output of said adder means (Σ2 and Σ1, respectively) as well as to said generator (Txau and Txtu, respectively); a command unit (CC3 and CC2, respectively) connected to the output of said control logic (LCau and LCtu, respectively) and suitable to generate a control signal (k) to modify the value of said matching impedance (Zau).

Claim 3

Device as in claims 1 and 2 characterized in that said control unit (CC) includes a first operational amplifier (AP4) with adder function of two signals arriving from a second operational not inverting amplifier (AP5) and from a third operational inverting amplifier (AP6) of unitary gain.

Claim 4

Method for the adjustment of the impedance (Ztu) of a subscriber termination to the characteristic impedance of the telephone line connecting the latter to the corresponding subscriber access in the exchange, in this access there is a programmed impedance (Zau) which is equal to the characteristic impedance (Zc) of said subscriber telephone line (LT), characterized in that there are the following operative phases programmed: a) emitting a first periodical reference signal (Etu) with a frequency (300 - 500 Hz) includes in the low range of the voice band (3000 - 3400 Hz) along the subscriber telephone line; b) measuring the level of said reference signal downstream from the matching impedance (Ztu); c) comparing this measured signal with a preset fraction of the reference signal (Etu) to find out the error signal (Ertu) turning out zero when the measured signal is equal to said preset fraction; d) generating a control coefficient (k) to modify the subscriber impedance value (Ztu) depending on said error signal (ERtu) until putting it to zero.

Claim 5

Method for the automatic adjustment of the adjustable impedance (Ztu) provided for between a subscriber set and the telephone line (LT) connecting it to the corresponding subscriber access (AU) in the exchange as well as to the adjustable impedance (Zau), provided for in the exchange, between the telephone line (LT) and the corresponding subscriber access (AU), characterized in that the following operative phases are scheduled: a) emitting from the subscriber termination a second periodical reference signal (Etu) with a frequency (3000 - 3400 Hz) included in the high range of the voice band along the subscriber telephone line (LT) controlling that the phase error (EFtu) connected with the subscriber set (TU) is equal to zero; b) emitting from the subscriber termination (TU) said first reference signal (300 - 500 Hz) adjusting the coefficient K in such a way that the local error function is cancelled; c) emitting from the subscriber access (AU) said second periodical reference signal (Eau) along the subscriber telephone line (LT) controlling that the phase error (EFau) connected to the subscriber access (AU) is equal to zero; d) emitting from the subscriber access (AU) the above mentioned first reference signal (300-500 Hz) adjusting the coefficient K in such a way that the local error function is cancelled.

Claim 6

Method for the automatic adjustment of the adjustable impedance (Ztu) foreseen in the subscriber termination along the telephone line (LT) connecting it to the corresponding subscriber access(AU) in the exchange as well as of the adjustable impedance (Zau) provided for in the exchange between the telephone line (LT) and the corresponding subscriber access (AU), characterized in that the following operative phases are programmed: a) emitting from the subscriber access (AU) said second periodical reference signal (Eau) along the subscriber telephone line (LT) checking that the phase error (EFau) connected to the subscriber access (AU) is different from zero; emitting from the subscriber termination (TU) said second periodical reference signal (Etu) along the subscriber telephone line (LT) checking that the phase error (EFtu) connected to the subscriber termination (TU) is different to zero; c) sending back from the subscriber access (AU) the above mentioned periodical reference signal (Eau) modifying the impedance provided for in the subscriber termination (Ztu) until the phase error measured at the subscriber access will be cancelled (EFau = 0), and therefore freeze the obtained subscriber termination impedance value; d) emitting further from the subscriber access(AU) the above mentioned first periodical reference signal adjusting the programmed impedance in the subscriber access until the amplitude error measured at the subscriber access (Erau) will be cancelled.

Claim 7

Method according to claims 4, 5 and 6 characterized in that said predetermined fraction is equal to 1/2.

Claim 8

Method according to claims 4, 5 and 6 characterized in that the above mentioned periodical reference signals have a frequency included between 300 and 3400 Hz.