| 摘要 |
747,541. Pulse modulation and shaping circuits. STANDARD TELEPHONES & CABLES, Ltd. June 8, 1954, No. 16769/54. Classes 40 (5) and 40 (6). A relaxation circuit of the type described in Specification 726,496 employing a transistor 1 with feed-back from the collector 4 over series circuit 5, 6 to the emitter 3 is held normally blocked by a battery 11 which maintains the emitter negative with respect to earth over conducting diode 12. The emitter and collector are connected over resistors 8, 10 to large positive and negative batteries 7, 9. Since only a very small collector current flows, its potential is near that of battery 9 and rectifier 15 is held non-conducting. A train of regularly recurring positive pulses is applied over transformer 13 each causing the circuit to generate a positive-going pulse at the collector which is limited near the potential of battery 32 due to diode 15 conducting. It is stated that the trailing edge of the collector pulse is determined by the potential on the collector and this is varied by speech applied over transformer 18, a capacitor 17 maintaining the potential constant during the generation of the pulse. Slicing circuit. The pulse at the collector is fed to a slicing arrangement comprising a normally conducting diode 29 and blocked diodes 21, 30 so that the output terminal 27 is at the potential of battery 25. When the pulse occurs, the collector potential rises, the junction of the diodes rising until diode 30 conducts thus carrying the output terminal to this level, Fig. 2 (not shown), since diode 21 conducts as soon as the junction rises above battery 11. The duration-modulated pulses may be converted to phase-modulated pulses by differentiating transformer 23, diode 26 suppressing the leading edge of the pulse. It is stated that the delay in the occurrence of the trailing edge is due to the time taken to collect stored minority carriers. In order to increase the percentage modulation, the pulses are reduced, an opencircuited delay line being used, Fig. 4 (not shown). |
