| 摘要 |
910,940. Automatic - exchange systems. TELEFONAKTIEBOLAGET L.M. ERICSSON. Feb. 25, 1959 [Feb. 25, 1958], No. 6582/59. Class 40 (4). In a system of the " resonant transfer " type the subscribers' storage devices are connected to their respective multiplex highways via current controlled switches, rendered conducting in the first instance by a brief pulse and being eventually rendered non-conducting by the current through them falling below a prescribed small value. As shown, each subscriber A is provided with a low-pass filter LP1 and a tuned circuit 13, 15 of period equal to twice the pulse duration, which circuit is connected to the common lead F1 by an NPNP type non-linear resistance which has a low resistance for high currents but high resistance for low currents. Subscriber B is connected similarly to common lead F2. Each common lead such as F1 is provided with a highimpedance source 36 consisting of an A.C. source feeding a pair of transistors 33, 34 in push-pull, which provides the lead with a positive-going half-sinusoid coincident with each channel period. To connect subscribers A and B a channel pulse period is allotted to the connection, and the primary windings 16, 29 and the transistor gate 24 between leads F1 and F2 are pulsed cyclically during these periods, the windings 16, 29 being provided only with a sharp pulse at the beginning of the period. The voltage induced in windings 15, 28 in combination with the half-sinusoid voltages applied to leads F1, F2 increases the current through the NPNP switches 17, 27 to reduce them to the low impedance state, so that the condensers 13 and 26 are connected to lines F1 and F2 which themselves are interconnected by the gate 24. Interchange of charge on the condensers 13, 26 thus takes place to effect communication between the subscribers. When the half-sinusoid current falls below a prescribed value the switches 17, 27 become non-conducting and energy transfer between the condensers ceases. Transistors 41, 42 are arranged to discharge the common leads F1, F2 between channel pulses. In an alternative arrangement, Fig. 1 (not shown), the half-sinusoid sources are dispensed with, and the lower portions of the filters LP1, LP2 are connected to opposite polarities and the directions of the switches connected to one of the common leads is reversed. The switching- off of the switches is then wholly controlled by the transfer current between the subscribers' storage condensers. Reference is also made to audio-frequency digit receivers being connected up by these means and to the possibility of an intermediate audio link between the common leads F1, F2. The NPNP switches may be replaced by other bi-stable elements such as avalanche transistors. Specification 737,417 is referred to. |
