| 摘要 |
1,174,458. Number senders; transistor oscillators. INTERNATIONAL BUSINESS MACHINES CORP. 2 Oct., 1967 [23 Dec., 1966], No. 44709/67. Headings H3T and H4K. In a signal generator of the type in which the frequency of an oscillator is varied by selecting an appropriate tap on the inductance in an LC circuit, a source of potential is directly connected to the capacitor of the LC circuit and is directly connectable through switching transistors to the tappings on the inductance. The Figure shows a dual tone generator for multi-frequency telephone signalling. A pair of transistors 66 and 75 oscillate when enabled at frequencies determined by the settings of their respective LC circuits 60-1 to 60-4 and 70-1 to 70-4, and the combined output is applied via an emitter follower 100 to an output transducer 104 coupled to the microphone of a telephone handset. To select a pair of frequencies, a single key of a set 96-1 to 96-10 is depressed supplying earth potential to one column of a diode matrix. This potential is applied via two row conductors to the base of one transistor of a set 76 to 82 and to the base of one transistor of a set 84 to 90. These transistors are thus switched to conduction supplying an enabling potential to the corresponding taps 60-1 to 60-4 and 70-1 to 70-4 causing the circuit to oscillate at the selected frequencies. |
