Voltage controlled oscillator having function of auto amplitude control

A voltage controlled oscillator having an automatic amplitude control is provided. A voltage controlled oscillator having an automatic amplitude control according to the present invention with a resonant circuit that generates resonant signal, and a differential amplifier circuit to generate the two oscillating signals having a phase difference from each other 180 ° and feeding back the resonance signal, the differential voltage-controlled oscillator comprises an active load for controlling the gain of the oscillating signal generated by the amplifier circuit; And an automatic amplitude control unit for comparison to the two after converting an oscillating signal to create a direct-current voltage DC voltage and the predetermined reference voltage to output a control voltage for determining the resistance of the active load. According to the invention, it is possible to effectively control the amplitude of the oscillation signal output, it is possible to reduce the phase noise according to the noise components introduced by the current source during switching of the differential amplifier circuit. A voltage controlled oscillator, VCO, automatic amplitude control, AAC, differential, resonance, the oscillation