Protection of a telephone line against overvoltages

1. A structure for protecting a first line and a second line against overvoltages lower than a negative threshold or higher than a positive threshold, comprising:

at least one thyristor connected between each of the first and second lines and a reference potential;

wherein, for all thyristors:

a metallization corresponding to an electrode on a gate side, wherein that metallization is in contact, by its entire surface, with a surface of a corresponding semiconductor region; and

the gate is directly connected to a voltage source providing a DC voltage defining one of said negative and positive thresholds.

2. The structure of claim 1 , wherein the positive threshold is zero, comprising:

each of the first and second lines is coupled to the anode of a diode and to the cathode of a cathode-gate thyristor, and cathodes of the diodes and the anodes of the thyristors are coupled to the reference potential;

a common negative DC voltage source connected to the two gates of the cathode-gate thyristors.

3. The structure of claim 2 , wherein the cathode-gate thyristors and the diodes are formed in a same monolithic component.

4. The structure of claim 1 , wherein:

each of the first and second lines is connected to the cathode of a cathode-gate thyristor and to the anode of an anode-gate thyristor, the anodes of the cathode-gate thyristors and the cathodes of the anode-gate thyristors being coupled to the reference potential;

the gates of the cathode-gate thyristors are directly connected to a common negative DC voltage source defining the negative threshold; and

the gates of the anode-gate thyristors are directly connected to a common positive DC voltage source defining the positive threshold.

5. The structure of claim 4 , wherein all thyristors are formed in a same monolithic component.

6. The structure of claim 1 , wherein at least one of the voltage sources is a power supply source of a Subscriber Line Interface Circuit (SLIC) for the first and second lines.

7. The structure of claim 1 , wherein at least one of the voltage sources comprises at least one battery.

8. A structure for protecting a first line and a second line against overvoltages lower than a negative threshold or higher than a positive threshold, comprising:

at least one thyristor connected between each of the first and second lines and a reference potential;

wherein:

all thyristors have no emitter short circuits; and

all thyristors have a semiconductor gate region maintained at one of a negative and positive DC potential by a gate electrode.

9. The structure of claim 8 , wherein the positive threshold is zero, comprising:

each of the first and second lines is coupled to the anode of a diode and to the cathode of a cathode-gate thyristor, and cathodes of the diodes and the anodes of the thyristors are coupled to the reference potential;

a common negative potential is maintained at the two gates of the cathode-gate thyristors.

10. The structure of claim 8 , wherein the positive threshold is zero, comprising:

each of the first and second lines is coupled to the anode of a diode and to the cathode of a cathode-gate thyristor, and cathodes of the diodes and the anodes of the thyristors are coupled to the reference potential;

a common negative potential is maintained at the two gates of the cathode-gate thyristors.

11. The structure of claim 8 , wherein the at least one thyristor is:

conductive when the voltage between one of the first and second line and the reference potential is greater than one of the positive DC potential and negative DC potential; and

non-conductive when the voltage between one of the first and second line and the reference potential is less than one of the positive DC potential and negative DC potential.