| 摘要 |
PURPOSE: A ring oscillator is provided to have an output voltage whose frequency is linearly changed according to a control voltage. CONSTITUTION: An attenuation portion(1) receives an input voltage(VI) and a reference voltage(VREF) and amplifies a difference between the reference voltage(VREF) and the input voltage(VI) to output a control voltage(VC) capable of being controlled finely. A PMOS transistor(PM1) is controlled by a bias voltage to supply a power supply voltage to an inverter(INV1). An NMOS transistor(NM1) is controlled by the control voltage to supply a ground voltage to the inverter(INV1). An inverter(INV2) inverts an output of the inverter(INV1). An NMOS transistor(NM2) and a capacitor(C1) are serially connected between an input terminal of the inverter(INV2) and the ground voltage, and the NMOS transistor(NM2) is controlled by the control voltage(VC). An inverter(INV3) inverts an output of the inverter(INV2). An NMOS transistor(NM3) and a capacitor(C2) are connected in series between an input terminal of the inverter(NM3) and the ground voltage, and the NMOS transistor(MN3) is controlled by the control voltage(VC).
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