| 摘要 |
918,932. Transistor mixing and oscillating circuits. PYE Ltd. Aug. 15, 1961 [Aug. 19, 1960], No. 28816/60. Class 40 (6). In a transistor oscillator, the oscillation frequency is maintained constant with supply variations by connecting in series with the collector a resistor, the value of which is equal to the product of a resistor connected in series with the emitter, and the working gain of the transistor when biased to produce the desired output power from the oscillator. In a first embodiment, Fig. 1, the local oscillator of a television receiver operating on Bands I and III comprises a Colpitts circuit, the frequency of oscillation of which is determined by coil L1, which may be interchanged with others to cover channels 1-12. A channel 13 coil, L2, is always in circuit, and a fine-tuning capacitor C1 is connected to a tap on this coil. Frequency variations with supply voltage are minimized by adjusting R2, R3 to give the required output, and then making R4 equal to BR1, where B is the gain in grounded emitter configuration. Changes in frequency with ambient temperature are compensated by employing capacitors of the negative temperature coefficient type for either C2 or C3 or both. In a second embodiment, Fig. 2, a self-oscillating mixer has its input applied to the base of transistor T2 from aerial coil L10. The oscillator circuit comprises the resonant circuit L12, C15, C17, C18 back-coupled by means of a further coil L13. The I.F. output is taken from resonant circuit L14, C16. Frequency variations with supply voltage are minimized as before by adjusting R12, R13 to give the required output and making R14 equal to BR11. Specification 918,931 is referred to. |
