Patent ID: 7301413

Claim:
A voltage controlled oscillator comprising: a voltage comparing circuit that receives a control voltage, a first reference voltage, and a second reference voltage to activate a first voltage comparison signal when the control voltage is lower than the first reference voltage and to activate a second voltage comparison signal when the control voltage is higher than the second reference voltage, the second reference voltage being higher than the first reference voltage; a counter that decrements a counter value while the first voltage comparison signal is activated and increments the counter value while the second voltage comparison signal is activated, in synchronization with a count clock; and an oscillating circuit that has a plurality of oscillation frequency bands different from one another, selects one of the oscillation frequency bands according to the counter value, and regulates an oscillation frequency according to the control voltage within the selected oscillation frequency band to output an output clock; wherein said oscillating circuit comprises: a plurality of internal oscillating circuits having oscillation frequency bands different from one another; and a selecting circuit that selects, according to the counter value, one of clocks generated by said internal oscillating circuits to output the selected clock as the output clock; and each of said internal oscillating circuits comprises: a plurality of inverting circuits connected in a ring; and a plurality of variable resistors provided between a power supply line and power supply terminals of said inverting circuits to be connected with the power supply line and the power supply terminals, respectively, and changing a resistance value according to the control voltage.