Abstract: Disclosed is a quadrature VCO (voltage controlled oscillator) which comprises a first delay cell including a first switching transistor and a second switching transistor, the first delay cell outputting first and second in-phase signals with different phases; and a second delay cell including a third switching transistor and a fourth switching transistor, the second delay cell outputting first and second quadrature-phase signals with different phases. The first and second quadrature-phase signals are applied to back gates of the first and second switching transistors, and the first and second in-phase signals are applied to back gates of the fourth and third switching transistors.