Voltage-controlled oscillator and integrated circuit device provided with it

A voltage-controlled oscillator comprising:

• a plurality of voltage-controlled oscillation circuits that oscillate at a frequency according to a control voltage;
• a selector circuit that selects one of the voltage-controlled oscillation circuits and makes the selected voltage-controlled oscillation circuit operate;
• and
• a limiter circuit that, if an output of the selected voltage-controlled oscillator is higher than a predetermined level, limits the output of the selected voltage-controlled oscillation circuit to the predetermined level,
• wherein, even when outputs of the plurality of voltage-controlled oscillation circuits have different levels, if the output of the selected voltage-controlled oscillator is higher than the predetermined level, an output of the limiter circuit is kept at a constant level.

A voltage-controlled oscillator comprising:

• a plurality of voltage-controlled oscillation circuits that oscillate at a frequency according to a control voltage;
• and
• a selector circuit that selects one of the voltage-controlled oscillation circuits and makes the selected voltage-controlled oscillation circuit operate,
• wherein variable oscillation frequency ranges of adjacent voltage-controlled oscillation circuits are so set as to overlap at ends thereof, and variable oscillation frequency ranges of the individual voltage-controlled oscillation circuits are so adjusted that an upper end frequency of an nth (where n≧1) voltage-controlled oscillation circuit as observed when most deviated on a low side is higher than a lower end frequency of mth (where m=n+1) voltage-controlled oscillation circuit as observed when most deviated on a high side.

An integrated circuit device comprising:

• a voltage-controlled oscillator including a voltage-controlled oscillation circuit that oscillates at a frequency according to a control voltage and a limiter circuit that, if an output of the voltage-controlled oscillator is higher than a predetermined level, limits the output of the voltage-controlled oscillator to the predetermined level,
• wherein, even when, according to the control voltage, the output of the voltage-controlled oscillator varies along with the frequency at which the voltage-controlled oscillator is oscillating, if the output of the voltage-controlled oscillator is higher than the predetermined level, an output of the limiter circuit is kept at a constant level,
• wherein the limiter circuit includes a differential amplifier circuit that receives the output of the voltage-controlled oscillation circuit and operates in a saturated state,
• wherein the differential amplifier circuit operates from an operation current produced by a constant current source that produces a constant current by applying a predetermined voltage to a current producing resistor.