Voltage-controlled oscillator circuit and voltage-controlled oscillating method

A voltage-controlled oscillating method in which an oscillating frequency is varied in response to an externally supplied control voltage, comprising the steps of:

• (a) providing n (n is an odd positive integer) inverters connected to each other in a serial connection;
• (b) producing a select signal based on a threshold voltage of a selector field-effect transistor;
• and
• (c) selecting one of an output signal from an (n−i)-th (0<i<n) of the n inverters and another output signal from an n-th one of the n inverters in response to the select signal produced in said (b) step, and supplying the selected signal to a first one of the n inverters,
• wherein said (b) step includes:
• (d) judging whether or not said threshold voltage of the selector field-effect transistor is smaller than or equal to a preselected value;
• (e) producing said select signal such that the output signal from said (n−i)-th one of n inverters is selected when a judgment result of said (d) step is made that the threshold voltage of said selector field-effect transistor is smaller than or equal to said preselected value;
• and
• (f) producing said select signal such that the output signal from said n-th one of n inverters is selected when a judgment result of said (d) step is made that the threshold voltage of said selector field-effect transistor is larger than said preselected value.

A voltage-controlled oscillator circuit comprising:

• n (n is an odd positive integer) inverters connected to each other in a serial connection;
• select signal producing means containing a selector field-effect transistor, for producing a select signal based on a threshold voltage of said selector field-effect transistor;
• and
• selecting means for selecting one of an output signal from an (n−i)-th one (0<i<n) of said n inverters and another output signal from an n-th one of said n inverters in response to the select signal produced in said select signal producing means,
• wherein said selecting means supplies said selected signal to a first one of said n inverters,
• wherein said select signal producing means includes:
• judging means for judging whether or not said threshold voltage of the selector field-effect transistor is smaller than or equal to a preselected value;
• first means for producing said select signal such that the output signal from said (n−i)-th one of n inverters is selected when a judgment result of said judging means is made that the threshold voltage of said selector field-effect transistor is smaller than or equal to said preselected value;
• and
• second means for producing said select signal such that the output signal from said n-th one of n inverters is selected when a judgment result of said judging means is made that the threshold voltage of said selector field-effect transistor is larger than said preselected value.