International Business Machines Corporation

Daniel F Reynes

Jean-Pierre L Suzzoni

Michel F Ferry

Emile Morlec

Jean-Claude C Grange

Nghiem H Tu

Philippe Hernandez

A switching network includes electronic crosspoint switches for providing electronic connection or disconnection between two voice stations. Each station is connected to the network through a line transformer. When two stations are connected to each other, the voice path in the network includes the secondary winding of the 1st station transformer, a series of crosspoint switches, a middle junctor, a series of crosspoint switches, and the secondary winding of the 2nd station transformer. Each middle junctor includes a negative resistance circuit which introduces a negative resistance in series with the voice path, thus compensating for the series losses in the network, and two negative inductance circuits connected on both sides of the junctor in parallel with the voice path, to compensate for the parallel losses, especially those introduced by the line transformers.

Device for increasing the parallel inductance of a transformer

A circuit associated with a telephone line to detect line status includes a first detector sensitive to the line current phase, a second detector sensitive to the ringing voltage phase, and two pulse generators of the same frequency as the ringing voltage, appearing at the positive and negative zero-crossings of the ringing voltage, respectively. When only the ringing current is applied to the line, only the signals from both detectors and one generator are simultaneously present (once per period). When the called subscriber lifts his handset, the signals from both detectors and the other generator are also simultaneously present once per period. These pulse coincidences are detected and processed by an appropriate logic.

Telephone line circuit

An inductive load driving amplifier is disclosed which includes two serially connected transistors, with Zener diodes limiting the collector-emitter voltage of the one and diverting the collector-base current of the other when the first one switches off. The driver is implemented as an integrated circuit. This collector isolation constitutes a high voltage Zener diode which contributes to limit the collector voltages. The combination of these features prevents the device from being exposed to second breakdown when switching highly inductive loads (e.g. several Henrys under 50V), thereby avoiding the harmful effects of breakdowns during switching.

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Villeneuve Loubet, France

Daniel F Reynes