A transformer feed-back quadrature voltage controlled oscillator (QVCO) includes a first VCO; a second VCO; and a dynamic phase error correction circuit, having a plurality of coupling capacitors connected between the first and second VCOs, wherein the capacitances of the coupling capacitors are varied according to a digital control signal to correct a phase error of local oscillating (LO) signals of quadrature phases output by the first and second VCOs.