A Truly Balanced Q-Band CMOS Frequency Doubler Based on Hybrid Quadrature Coupler

In this letter, a truly balanced CMOS Q-band frequency doubler with an ultra-compact differential hybrid quadrature coupler is demonstrated using 90-nm CMOS technology. The doubler incorporates two Gilbert-cells fed by I/Q signals to compensate the time delay from transconductance stage and avoid output DC offset, providing truly balanced differential outputs. The doubler achieves a 3-dB bandwidth from 40 to 49 GHz with a minimum conversion loss of 1.6 dB at 44 GHz, while the output amplitude imbalance is measured to be less than 0.7dB. The measured I/Q mismatch of the quadrature coupler is less than 1° within 10 GHz bandwidth. The doubler chip consumes 9.6 mA from a 1.2-V supply, and the chip dimension is 0.7 × 0.9 mm².