Abstract: The present invention relates to a circuit providing frequency-doubling function. More particularly, the present invention relates to a frequency doubler circuit comprising dual Gilbert mixers in replace with the single mixer scheme in the conventional direct conversion transceiver circuit. CMOS technology is preferred in order to lower size and power consumption of the specific IC. With a balanced output load, either is resistor-capacitor (RC) load, resistor-inductor (RL) load, or a combination of the three (RLC), symmetrical output waveforms are obtained thereby. Notice that two quadrature inputs and their inverse-phase signals are provided to the purposed dual Gilbert mixer circuit, and two outputs in inverse-phase are obtained accordingly as meditated in this invention.