| 摘要 |
982,165. Valve and transistor oscillating circuits; frequency modulation. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Jan. 30, 1963 [Feb. 2, 1962; Oct. 10, 1962], No. 3842/63. Headings H3F, H3R and H3T. An oscillator of high frequency stability comprises a transistor with a stabilizing resistor 2, Fig. 1, in the emitter lead and a tuned circuit 4 in the base circuit, to which positive feedback is applied by means of a coupling inductor 3 in the collector circuit. In addition, negative feedback is applied to the oscillator by means of a second coupling inductor 8 in the collector circuit, which is connected in series with two rectifier diodes 9, 10 having different threshold bias voltages. The diodes permit the passage of current through the negative feedback inductor only during the peak values of the oscillations produced by the oscillator and so determine the amplitude of oscillation. The bias applied to the diodes 9, 10 may comprise a synchronizing signal. In a modification (Fig. 2, not shown), the two diodes are replaced by a single Zener diode. The arrangement may be modified to form a modulator for frequency modulation. In the modification the feedback to the tuned circuit 4, Fig. 3, includes, in addition to positive and negative feedback over inductors 3, 8 respectively a capacitive feedback over capacitor 17, derived from the output load 7. In this way the effective capacity shunting the tuned circuit 4 depends upon the gain of the transistor, which is varied by the modulating signals, the latter being applied to the base over resistor 5. The emitter-circuit resistor 2 is by-passed for the modulating signals by a capacitor 15. The capacitor 15 may be replaced by an inductor, or may alternatively be connected to the emitter, instead of to the collector circuit of the transistor, the capacitor 15 then being omitted. The transistor may in every case be replaced by a thermionic valve. |
