Patent GB-849873-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/52
Filed: 1957-08-13
Abstract: 849,873. Automatic exchange systems. PHILIPS ELECTRICAL INDUSTRIES Ltd. Aug. 13, 1957 [Aug. 16, 1956], No. 25533/57. Class 40 (4). In an arrangement for establishing a connection between one of a plurality of inlets and one of a plurality of outlets via two or more stages of conductors interconnected by transistor matrices, the transistors of which are normally rendered non-conductive by connections via impedances to suitable voltage sources, the transistors are arranged in groups each consisting of a number of transistors the emitters of which are connected to different conductors of the same stage, the collectors of which are connected to conductors of the subsequent stage, and the bases of which are connected via individual resistors to the same marking conductor, and a marker, having selected a free path, marks the inlet and each marking conductor associated with a group of transistors the collector of one transistor of which is connected to a conductor in the selected path, whereupon the transistors in the selected path are successively rendered conductive starting with that connected to the inlet. Trunking arrangements.-The system described consists of a plurality of primary frames and a plurality of secondary frames, the numbers of frames for a 10,000-line exchange being twenty and ten, respectively. Each primary frame, such as LF1 (Fig. 1), consists of a number (e.g. ten) of primary contact groups such as PP1, PPm, and a number (e.g. ten) of secondary. contact groups such as PS1, PSm; and each secondary frame, such as TF1 (Fig. 2), of primary contact groups, such as SP1, SPm, and secondary contact groups, such as SS1, SSm. In each frame each primary contact group is connected by a link, such as A111, C111, to each secondary contact group, and each secondary contact group of each primary frame is connected via a trunk, such as B111, to the corresponding primary contact group of each secondary frame. The inlets, outlets, links, trunks and transistors are designated in accordance with the following seven indices: (a) the number of the outlet in the primary contact group of the relevant primary frame; (b) the number of that contact group; and (c) the number of that frame ; (d) the number of the secondary contact group in the primary frame, which is the same as the number of the primary contact group of the secondary frame to which the outlet is connected; (e) the number of the secondary frame ; (f) the number of the secondary contact group in that frame; and (g) the number of the inlet in that group. An outlet is designated by Labc, a primary frame link by Abed, a trunk by Bcde, a secondary frame link by Cdef, and an inlet by Tefg; a primary frame primary contact (transistor) by LAabcd, and a secondary one by ABbcde; a secondary frame primary contact (transistor) by BCcdef, and a secondary one by CTdefg. Operation.-All the links and trunks are connected through individual resistances, of say 20K, to sources - V2 having a voltage of - 20 volts, and the bases of the transistors are connected through individual resistors, of say 10K, to marking conductors such as ML11, MA11. In each primary frame the bases of all primary transistors connected to outlets having the same index figure (a) are connected to the same marking conductor designated MLac, and the bases of all secondary transistors connected to links leading to the same primary contact group and thus having the same index (b) are connected to the same marking conductor MLbc. In each secondary frame the bases of the primary transistors connected to trunks leading to the same primary frame and thus having the same index (c) are connected to the same marking conductor MBce, and the bases of the secondary transistors connected to links leading to the same primary contact group and thus having the same index (d) are connected to the same marking conductor MCde. All the marking conductors are normally at + 5 volts, the outlets at - 10 volts, and the inlets at ground potential, and all the transistors are therefore non-conductive. In order to establish a connection between an inlet and an outlet a marker (not shown) receives the identity of the inlet (efg) and that of the outlet (abc) and tests for free links and trunks between them. These if free have a voltage of - 20 volts, and if busy of about - 10 volts, these potentials enabling the marker to distinguish free ones from busy ones. Thus for a connection to be set up between inlet T111 and outlet L111 the marker tests A111, B111, C111 and A11m, B1m1, Cm11, respectively, selecting a free path, say the latter which is indicated in thick lines in the drawings. Transistors CTm111, BC1m11, AB11m1 and LA111m now require to be made conductive. To this end the marker reduces the potential of the marking conductors ML11, MA11, MB11 and MCm1 to + 2 volts thus marking all the transistors which are ringed in the drawings, and in addition applies an alternating voltage to transformer TT111 so as to raise the potential on the inlet T111 periodically to + 3 volts. Transistor CTm111 thereupon conducts and since the collector current exceeds the emitter current the difference current flows in the base resistor WTm111 thus reducing the base voltage so as to maintain CTm111 conducting even after the marking voltages have been removed. The voltage of link Cm11 rises to a value substantially equal to that of Till, since RCm11 has a high value with respect to TR111, and BC1m11 therefore conducts. Transistors AB11m1 and LA111m conduct successively in like manner, whereafter the voltage of A11m, B1m1 and Cm11 decreases to about - 10 volts (-V1) due to the resistance of the winding of TL111 being comparatively low with respect to that of RT111. The required connection is thus established. Release of the connection is effected by applying a negative pulse via TTT111 to the emitter of CTm111 thus cutting this transistor off. The potential of Cm11 then falls to - 20 volts (- V2) whereupon BC1m11 is cut off. AB11m1 and LA111m are cut off in succession in like manner. If it is desired to use two markers simultaneously the markers must not simultaneously mark transistors the emitters of which are connected to the same link or trunk. They may, however, mark simultaneously transistors in different frames.