| 摘要 |
PURPOSE:To adjust the frequency with a high precision in a wide range by providing a varicap diode as a coupling capacitor between two feedback amplifying transistors (TR) in a local oscillator using an SAW filter. CONSTITUTION:Varicap diodes 13 and 14 are provided between two feedback amplifying TRs 7 and 8 instead of the coupling capacitor. Adjusting voltages are applied to diodes 13 and 14 from a point E to vary coupling capacitires of both diodes 13 and 14. Then, phase characteristics in the amplifier circuit side viewed from points C and D are changed, and the adjustment of frequency + or -200 kHz is possible for 0.5-7pH capacity variation. Further, the loss due to the variation of the degree of coupling is small because the capacities are changed simultaneously by both diodes 13 and 14. Thus, the frequency is adjusted with a high precision in a wide range. |
