| 摘要 |
PROBLEM TO BE SOLVED: To perform switching between a variable mode and a fixed mode and to set the frequency division ratio of a reference counter for a PLL frequency synthesizer circuit. SOLUTION: This PLL frequency synthesizer circuit, which is provided with a crystal oscillator 20, the reference counter 33, a voltage controlled oscillator 30, a programmable counter 27, a loop filter 29 and a phase comparator 28, outputs the output signal of the oscillator 30 and has a mode changeover switch 7 that selects either or both modes between the fixed mode in which a desired piece of frequency division ratio data among pieces of frequency division ratio data stored in a counter value holding circuit 2 is inputted to both the counters 27 and 33, and the variable mode in which frequency division ratio data outputted from a shift register 26 is inputted to either or both counters 27 and 33.
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