| 摘要 |
PURPOSE:To shorten the channel switching time and improve S/N, by setting the product between the frequency modulation sensitivity of a voltage tuning oscillator and the frequency division ratio of a variable frequency divider to a constant approximately within a range of the operating frequency. CONSTITUTION:An oscillation frequency fV of a voltage tuning oscillator 1 not only has a signal output fout taken out but also is applied to a mixer 3 through an amplifier 2, and the differential frequency between this oscillation frequency and a reference frequency fR is applied from the mixer 3 to a variable frequency divider 6. The frequency fR is set to a frequency slightly higher than the frequency fV by multiplying an oscillation frequency fO of a quartz oscillator 4 M- number times in a multiplier 5. The frequency divider 6 divides the input frequency to 1/N and inputs the divided frequency to a phase comparator 7. The comparator 6 compares the phase of the signal from the frequency divider 6 with that of an output frequency fr of a fixed frequency divider 8 which divides the frequency fO to 1/K, and the oscillator 1 is controlled through an LPF9 by the differential output to constitute a PLL. A modulation sensitivity KV of the oscillator 1, the frequency division ratio N, and frequencies fV, fR, and fr are so set that the product between the modulation sensitivity KV and 1/N is constant approximately in the used frequency, thereby shortening the frequency switching time and reducing the noise to the oscillator 1. |
