US Patent 10333530 Voltage-controlled oscillator and phase locked loop having voltage-controlled oscillator

According to one embodiment, a voltage-controlled oscillator includes a voltage-current conversion circuit and hold circuit that outputs a first current corresponding to a control voltage, a current addition circuit that outputs a second current corresponding to the first current, and a current subtraction circuit that outputs a third current corresponding to the first current. The voltage-controlled oscillator also includes a narrow-band low-pass filter that passes a current in a first frequency band to reduce noise of the second current, a voltage-current converter that outputs a sixth current corresponding to a fifth current obtained by subtracting the third current from a fourth current corresponding to the control voltage, and a low-pass filter that passes a current in a second frequency band to reduce noise of the sixth current. The second frequency band is different from the first frequency band. The voltage-controlled oscillator further includes a current-controlled oscillator that oscillates a clock signal in accordance with a combined current of the second current and the sixth current.