Patent GB-888196-A (GB)
Title: Improvements in or relating to switching stages for selecting arrangements and to selecting arrangements incorporating such switching stages
IPC: H03K17/74
Filed: 1958-03-19
Abstract: 888,196. Automatic exchange systems. SIEMENS & HALSKE A.G. March 19, 1958 [March 20, 1957 ; April 12, 1957; July 19, 1957 ; Feb. 18, 1958], No. 8806/58. Class 40 (4). A circuit for indicating the first free device of a group of devices consists of a number of stages, one per device in the group, each stage having a coupling input to which either a " go " potential or a " stop " potential may be applied, a testing input to which either a " free " potential or a " busy " potential is applied indicative of the state of the corresponding device, a marking output at which is produced either a " mark " potential or a "neutral" potential and a coupling output at which is produced either a " go " potential or a " stop " potential. Each stage is so arranged that only if " go " and " free " potentials are applied to its inputs does the " mark " potential appear at the marking output, while the coupling output assumes the " stop " potential, whereas if " stop " potential is applied to the coupling input, the coupling output assumes " stop " potential. If " go " potential is applied to the coupling input and " busy " to the testing input, " neutral " appears at the marking output and " go " at the coupling output. Circuits of typical stages.-A stage which satisfies these conditions may be constructed from three diodes, a resistor and an inverting circuit, viz. a circuit in which a low input results in a high output and a high input in a low output. The two values which each potential can assume are referred to as the positive and negative potentials, these terms being used relatively to the means of the two values which may be arbitrarily chosen. A stage for which the " free," " go," and " marking " potentials are all positive is shown in Fig. 3, the inverting circuit being represented by the inverted triangle I. The resistor R1 and diode G3 form an " and " gate which applies the positive " marking " potential to the marking output z only when the testing input p and the coupling inprint k1 both receive the positive potential, while the negative output from I is transmitted via diode G2 to the coupling output k2. With the negative " busy " potential at p and positive at k1, z receives the negative " neutral " potential, and the positive " go " potential appears at k2. With the negative " stop " potential applied to k1, z receives the negative " neutral " potential, which negative potential also appears at k2, any positive output from I being ineffective as G2 is backed off. Stages are described for use with negative " free " and positive " go " and " marking " potentials (Fig. 5), with positive " free " and " marking " and negative " go " potentials (Fig. 7), with positive " free " and " go " and negative " marking " potentials (Fig. 8), and with positive " free," " go," and " marking " potentials (Fig. 9). Reversal of the polarity of all the diodes in Figs. 3, 5, 7, 8 and 9 results in stages suitable for use with potentials of the opposite sign in each case. Stage employing one transistor.-A stage for use with positive " free," " go " and " marking " potentials is shown in Fig. 10. The " and "-gate R2, G5 functions similarly to R1, G3 of Fig. 3 to produce the positive " marking " potential at z only when p and k1 are both positive, while the transistor T1, having its emitter and base at the same potential, passes no current, so that the negative potential Uv1 appears as negative " stop " potential at k2. With negative " busy " potential on p and positive on k1 z receives the negative " neutral " potential, and, with negative on its base, T1 conducts, its positive collector potential appearing as positive " go " potential at k2. Negative on k1 sends z negative and renders T1 non- conductive so that negative from Uv1 appears at k2. A stage for use with negative " free , " go " and " marking " potentials may be obtained by replacing T1 by an NPN transistor, reversing the polarity of G5, and changing Uv1 to a positive source. Stage using two transistors of the same type of conductance.-A stage employing two PNP transistors for use with positive " free," " go," and " marking " potentials is shown in Fig. 11. A negative voltage source Uv2 is connected to k2 and z and the potential of the positive source Uv3, connected via resistor R10 to the base electrode of transistor T3, is so chosen that when T2 and T3 are non-conductive the potential of the base of T3 is slightly more negative than the " go " potential. With positive potential connected to p and k1, the transistor T2 is non- conductive and the potential from Uv2 appears as " stop " potential at k2. T3, however, conducts and its positive collector potential appears as " marking " potential at z. With negative on p and positive on k1, transistor T2 conducts so that its positive collector potential appears as " go " potential at k2 and is also applied to the base of T3. T3 becomes non-conductive and the negative potential from Uv2 appears as " neutral " potential at z. With negative " stop " potential on k1, both transistors are non-conductive and both z and k2 receive the negative potential from Uv2. Using two transistors of different types of conductance.-In the stage shown in Fig. 12, T3 is an NPN transistor and the potential of source Uv4 is so chosen that when T2 and T3 are non- conductive the base of T3 is slightly more negative than its emitter potential (determined by Uv2). With positive at k1 and p, T2 is again non-conductive and the potential from Uv2 appears at k2. The resistors R9 and R10 are such that the base of T3 is slightly positive with respect to Uv2, so that T3 conducts and the resulting positive emitter potential appear at z. With negative (busy) at p and positive at k1, T2 conducts and its positive collector potential appears at k2, but T3 is non- conductive, so that negative from Uv2 appears at z. With negative on k1 neither transistor conducts so that negative from Uv2 appears at z and k2. Arrangement of stages to form a multi-stage circuit.-The circuit may be arranged so that the devices have a particular order of choice each hunting operation starting by testing the first choice device. In this case the coupling output k2 of every stage except the last is connected to the coupling input k1 of the next succeeding stage and a hunt is initiated by connecting the " go " potential to the coupling input k1 of the first stage. The marking outlet of the stage corresponding to the first free device then assumes the marking potential. In order to avoid the disadvantages inherent in this arrangement the hunt may be started at a different device on each occasion. To this end the stages are arranged in a closed chain and a contact t is interposed between the coupling output k2 of each stage and the coupling input k1 of the next stage, one of these contacts being open and the others closed. As shown in Fig. 2, when the contact ta is open the stage A becomes the one at which the hunt will commence. A control circuit (not shown) may advance the starting point one stage after each hunt. In order to ensure that only one device of the group is marked it is necessary that the " stop " potential be applied to the coupling output of a stage before the " marking " potential is applied to its marking output. Difficulty can also arise if a busy device which precedes the first free device becomes free during the testing period, so that the device initially marked as the first free one is then no longer marked as such due to the marking of the one which precedes it. Modifications which ensure that only one device of the group can be marked.-A bi-stable circuit is incorporated in each stage, which circuit is triggered if its corresponding device is free when a hunt is to take place, the arrangement being such that " stop " potential is then applied to the coupling output and neutral potential to the marking output of each stage until a predetermined time after the cessation of the triggering conditions, whereupon the marking output of the stage corresponding to the first free device is marked. Such a modified stage, in which the bi-stable circuit comprises the two tubes E and I, is shown in Fig. 15, which also depicts the control circuit S1 which initiates a hunt. In the inoperative state the tube I carries current in each stage so that its cathode is positive, whereas the tube E carries no current, its negative cathode potential being applied as " neutral " potential to z. The tube of the control circuit S1 also carries current, its positive cathode potential being applied as " go " potential to k1 and thence via G1, G2 to k2. The positive " free " potential is so chosen as not to be capable of rendering tube E conductive. When a hunt is to be performed a negative pulse is applied to the input w of the control circuit S1 to cut off the tube thereof. The resulting positive impulse produced at its anode is differentiated in each stage by the condenser C1 and the relatively short positive pulse produced from the leading edge of that impulse is applied to the grid of the E tube. In each stage corresponding to a free device this pulse in combination with the positive potential on p renders the tube E conductive, thus cutting off the tube I, the negative cathode potential of which is applied as " stop " potential to k2. At the same time the negative cathode potential of the tube in S1 is applied as " stop " potential the the coupling input k1 of the first stage, so that the marking outlets of all stages receive the negative " neutral " potential. When the negative impulse applied to w ceases, the tube in S1 again conducts. The restoration of tubes E by negative pulses produced by the condensers C is prevented by the diodes G6, but the rise in cathode potential is applied as " go " potential to k1 of the first stage, whereupon the first of the stages having its tube conducting applies positive " marking " potential to its marking outlet z. The trigge