| 摘要 |
1,013,159. Electric selective signalling systems. STANDARD TELEPHONES & CABLES Ltd. Oct. 26, 1962 [Oct. 28, 1961], No. 40614/62. Heading G4H. [Also in Division H3] In a circuit for converting a 1-out-of-x representation of data into a corresponding number of pulses an appropriate number of diodes in a chain of series-connected tunnel diodes TD1 to TD4, Fig. 1, having progressively increasing switching voltages, are simultaneously switched from their normal high impedance state to a low impedance state and then they are sequentially switched back to their high impedance states. As described, data in a 1-out-of-5 input code is entered by depressing and releasing an appropriate key K1 to K5 and output pulses are produced by a monostable circuit OS on a lead a or a lead b. Depression of a key changes some of the diodes to the low impedance state and release of the key produces a positive pulse at a point P which, via a capacitor Ck, turns on the monostable circuit OS (" on "=Tr1 conductive, Tr2 non-conductive). While this circuit OS is on a transistor Tr3 controlling current flow through the diodes is cut off and a capacitor C charges. Eventually the monostable circuit OS turns off-thereby marking the end of the first output pulse-but transistor Tr3 remains cut off for a further period determined by a circuit R1, C. When capacitor C is discharged transistor Tr3 becomes conductive and the normal relatively high voltage is applied across the chain of diodes. If, when this occurs, any diode is in its low impedance state then that one with the lowest switching voltage changes to its high impedance state first and in so doing it produces a positive pulse at P as before. This immediately turns on the monostable circuit OS which, in turn, cuts off the transistor Tr3 so that no more diodes can change their states at this instant. A further output pulse is then produced as before and the sequence repeats until every switched diode is returned to its normal high impedance state. Thus the output pulses have a length determined by the recovery time of the monostable circuit and the gaps between the output pulses is determined by the time constant R1C. |
