| 摘要 |
908,100. Transistor amplifier circuits; radio signalling. ALBISWERKE ZURICH A.G. Aug. 4, 1961, No. 28445/61. Classes 40 (5) and 40 (6). In the standby condition of a transistor amplifier the input stage is operated under class B conditions and a further stage is inoperative, whereas when a signal is received the input stage is switched to operate under class A conditions and the further stage is switched into operation. In the " personal call " receiver shown the line U sch is normally at zero voltage so that the two input stages H 1 , H 2 succeeding the aerial circuit A are biased to operate under class B conditions while the further stages E are not energized. The receipt of a signal will cause a switch E to operate and so energize stages E and convert the input stages to class A operation. Under class B conditions the input impedance and the gain of the input stages is high but a starting pulse preceding the calling pulse code will cause the switch S to operate and the resulting change to class A conditions will broaden the band-width so that these pulses are not distorted. Frequency selective calling codes may alternatively be used in which case the circuit must be tuned to the first frequency of the code. The invention may also be applied to audio frequency stages. |
