| 摘要 |
To output desired high purity signals, a frequency synthesizer was made to synthesize reference signals from a first and second signal generators in the same frequency band as a desired frequency band. Thereby, the resolution of the frequency synthesizer becomes twice the step DELTA F. Also, the frequency synthesizer can interpolate the step size of the first signal generator with half the number of steps. While, heretofore, the 100 MHz step size was interpolated with Fq=0, 10, 20, 30, 40 and 50 MHz, Fq=0, 20, 40 MHz interpolation is made possible. This permits the synthesis of 580 MHz to 1280 MHz. In this case, however, the minimum difference between the sum and difference frequencies from the first and second signal generators is 40 MHz and the lowest frequency is 20 MHz. Thus, depending on mixer isolation, the spurious measures become difficult. The frequency synthesizer of the present invention pays attention to the fact that 20 MHz step signals can be synthesized at frequencies which are integral multiples of Fq (multiples of 0 and 5 are excluded). When two-fold Fq is used, the minimum difference between the sum and difference frequencies output from a mixer is 80 MHz and the lowest used frequency is 40 MHz. The spurious measures by a PLL circuit becomes easy. A frequency detector forces the free-running frequency of a VCO included the PLL circuit. Control Data P and Q to the first and second signal generators are supplied from a control section based on data Fi set by a frequency setting section.
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