Analysis and Design of X Band CMOS Quadruture VCO using Transformer-Resonator Coupling with Deep mode switching

A fully integrated X-Band quadrature VCO is presented. The VCO is implemented using transformer-coupled resonator in 0.18 μm CMOS technology, in which two VCOs are coupled by direct current modulation method to generate I-Q signals. The VCO is realized employing the drain-gate transformer feedback configuration proposed here. This allows VCO to use the quality factor enhancement in coupled resonator using a transformer and the deep switching-off technique. By turning off switching transistors of the differential VCO core deeply, the phase noise performance is improved more than 10 dB. The measured phase noise values are -110 and -118 dBc/HZ at the offset frequencies of 600 kHz and 1 MHz respectively, which is about 10 dB better than the previously reported quadrature Si VCOs in 5 ~ 12 GHz frequency range. The tuning range of 250 MHz is achieved with the control voltage from 0 to 1 V. The VCO draws 8 mA in two differential core circuits with 3 V supply.