| 摘要 |
PURPOSE:To prevent the malfunction of a front frequency divider by inserting a filter, which attenuates a higher-harmonic component contained in a local oscillation output, between the amplitude-limiting amplifier and front frequency divider of a PLL frequency synthesizer channel-selecting circuit. CONSTITUTION:A power-source switching circuit 4 is controlled by an U/V switching control signal from a channel-selecting operation part 3 to put an UHF local oscillator 1 or a VHF local oscillator 2 in operation, and its output is inputted to an amplitude-limiting amplifier 7 through a filter 5 or 6. A signal processed through the amplitude-limitation of the amplifier is removed from higher harmonic through a higer-harmonic removing filter 13 and inputted to a front frequency divider 8. A signal whose frequency is divided by N by the frequency divider 8 is further divided by a variable frequency divider 9 at a frequency-division ratio 1/n which corresponds to the channel selection signal T of the channel-selecting operation part 3, and its output is compared with a signal from a reference oscillator 11 by a phase comparator 10. The output of the comparator 10 is supplied as a channel selection signal VC to the oscillator 1 or 2 through an LPF12. The outputs of the oscillators 1 and 2 are supplied to a mixer respectively. |
