| 摘要 |
PURPOSE:To reduce the degrading of the Q of an oscillation circuit by connecting a forward resistance of a diode in parallel between a collector an emitter of a switching transistor (TR) in terms of AC in a voltage controlled oscillator used for a frequency synthesizer. CONSTITUTION:A diode and a resistor 11 are connected in series between a collector of a switching TR3 and a control terminal and the anode of the diode 10 is connected to common in terms of AC by a capacitor 12. When the TR3 is turned on, the diode 10 is conducted, and an on-resistance 11 of the diode 10 is connected in parallel with an on-resistance 11 between the collector and emitter of the TR3. Since the capacitor 12 connected to the anode of the diode 10 is sufficiently larger than the capacitor 7, the capacitor 12 is neglected while being considered to be short-circuited in terms of AC. Thus, resistors 3a, 10a are connected in parallel and the resistance value between the capacitor 7 and common 9 is smaller than that of a conventional oscillator, then the degrading of Q of the oscillation circuit with the TR3 turned on is decreased. That is, the deterioration in the C/N and S/N is reduced.
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