Signal generation circuit, frequency measurement device including the signal generation circuit, and signal generation method

1. A signal generation circuit comprising:

a first signal source that generates a first signal; and

a variable rate frequency divider section that generates a variable rate frequency-divided signal in which a first frequency-divided signal obtained by frequency-dividing the first signal by a first frequency dividing ratio and a second frequency-divided signal obtained by frequency-dividing the first signal by a second frequency dividing ratio temporally alternately appear in a specified mixing ratio, the variable rate frequency divider section being structured to generate the variable rate frequency-divided signal through repeating:

step 1 adding a first constant indicating a ratio of the first frequency-divided signal included in the variable rate frequency-divided signal to a first variable;

step 2-1, when the first variable after the addition becomes greater than or equal to a result of addition of the first constant and a second constant indicating a ratio of the second frequency-divided signal included in the variable rate frequency-divided signal, outputting the first frequency-divided signal, subtracting the first constant and the second constant from the first variable, and returning to step 1); and

step 2-2, when the first variable after the addition becomes smaller than a result of addition of the first constant and the second constant, outputting the second frequency-divided signal and returning to step 1.

2. A frequency measurement device comprising:

the signal generation circuit recited in claim 1 ;

a source of signal to be measured that generates a signal to be measured:

a counter section that outputs a count value obtained by counting the number of changes in the signal to be measured included in a specified period that is decided based on the variable rate frequency-divided signal; and

a low-pass filter that removes high frequency components included in the count value.

3. A frequency measurement device according to claim 2 , the first frequency dividing ratio, the second frequency dividing ratio and the mixing ratio of the variable rate frequency-divided signal being decided based on pre-obtained noise level distribution characteristics versus frequency ratios between the frequency of the variable rate frequency-divided signal and the frequency of the signal to be measured.

4. A frequency measurement device according to claim 3 , an operating point parameter being defined by the fractional part of a ratio x/y where x is the frequency of the signal to be measured and y is the frequency of the variable rate frequency-divided signal, the frequency of the signal to be measured, and the first frequency dividing ratio, the second frequency dividing ratio and the mixing ratio of the variable rate frequency-divided signal being decided such that the value of the operating point parameter does not become a neighborhood value of a specified rational number where noise level increases.

5. A frequency measurement device comprising:

the signal generation circuit recited in claim 1 ;

a reference frequency signal source that generates a reference frequency signal;

a counter section that outputs a count value obtained by counting the number of changes in the variable rate frequency-divided signal included in a specified period that is determined based on the reference frequency signal; and

a low-pass filter that removes high frequency components included in the count value.

6. A frequency measurement device according to claim 5 , the first frequency dividing ratio, the second frequency dividing ratio and the mixing ratio of the variable rate frequency-divided signal being decided based on a pre-obtained noise level distribution characteristic versus a frequency ratio between the frequency of the variable rate frequency-divided signal and the frequency of the reference frequency signal.

7. A frequency measurement device according to claim 6 , an operating point parameter is defined by the fractional part of a ratio x/y where x is the frequency of the variable rate frequency-divided signal and y being the frequency of the reference frequency signal, the frequency of the reference frequency signal, and the first frequency dividing ratio, the second frequency dividing ratio and the mixing ratio of the variable rate frequency-divided signal being decided such that the value of the operating point parameter does not become to be a neighborhood value of a specified rational number where noise level increases.

8. A signal generation method comprising:

a step of, based on a first signal having a specified frequency, generating a first frequency-divided signal obtained by frequency-dividing the first signal by a first frequency dividing ratio and a second frequency-divided signal obtained by frequency-dividing the first signal by a second frequency dividing ratio; and

a process of repeating:

a step 1) of adding a first constant indicating a ratio of the first frequency-divided signal included in a variable rate frequency-divided signal to be generated to a first variable;

a step 2-1) of, when the first variable after the addition becomes greater than or equal to a result of addition of the first constant and a second constant indicating a ratio of the second frequency-divided signal included in the variable rate frequency-divided signal, outputting the first frequency-divided signal, subtracting the first constant and the second constant from the first variable, and returning to the step 1); and

a step 2-2) of, when the first variable after the addition becomes smaller than a result of addition of the first constant and the second constant, outputting the second frequency-divided signal and returning to the process 1),

thereby generating the variable rate frequency-divided signal in which the first frequency-divided signal and the second frequency-divided signal temporally alternately appear in a specified mixing ratio.

9. A frequency measurement device comprising:

a signal generation circuit that includes:

a first signal source that generates a first signal; and

a variable rate frequency divider section that generates a variable rate frequency-divided signal in which a first frequency-divided signal obtained by frequency-dividing the first signal by a first frequency dividing ratio and a second frequency-divided signal obtained by frequency-dividing the first signal by a second frequency dividing ratio temporally alternately appear in a specified mixing ratio,

a reference frequency signal source that generates a reference frequency signal;

a counter section that outputs a count value obtained by counting the number of changes in the variable rate frequency-divided signal included in a specified period that is determined based on the reference frequency signal; and

a low-pass filter that removes high frequency components included in the count value,

the first frequency dividing ratio, the second frequency dividing ratio and the mixing ratio of the variable rate frequency-divided signal being decided based on a pre-obtained noise level distribution characteristic versus a frequency ratio between the frequency of the variable rate frequency-divided signal and the frequency of the reference frequency signal.

10. A frequency measurement device according to claim 9 , an operating point parameter is defined by the fractional part of a ratio x/y where x is the frequency of the variable rate frequency-divided signal and y being the frequency of the reference frequency signal, the frequency of the reference frequency signal, and the first frequency dividing ratio, the second frequency dividing ratio and the mixing ratio of the variable rate frequency-divided signal being decided such that the value of the operating point parameter does not become to be a neighborhood value of a specified rational number where noise level increases.