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A diode-ring coupling technique has been used to design quadrature voltage-controlled oscillators (QVCOs), which consist of two n-core VCOs. The proposed CMOS QVCOs have been implemented with the TSMC 0.18 lm CMOS technology. A single-band and a dual-band QVCOs have been implemented to support the feasibility of the coupling technique. The die area of the single-band QVCO is 0.506 Â 0.905 mm 2 . At the supply voltage of 0.54 V, the total power consumption is 1.78 mW. The free-running frequency of the QVCO is tunable from 4.295 to 5.185 GHz as the tuning voltage is varied from 0.0 to 1.1 V. The measured phase noise at 1 MHz frequency offset is À114 dBc/Hz at the oscillation frequency 4.587 GHz, and the figure of merit of the proposed QVCO is À184.73 dBc/Hz.

A new fully integrated, CMOS Clapp quadrature voltagecontrolled oscillator (QVCO) is presented. The QVCO is composed of two differential n-core Clapp VCOs coupled by four pMOSFETs and was implemented in the 0.18-lm CMOS technology with 0.9-V supply voltage. The die area is 0.574 Â 0.866 mm 2 . At the supply voltage of 0.9 V, the total power consumption is 12.2 mW. The free-running frequency of the QVCO is tunable from 7.89 to 9.3 GHz as the tuning voltage is varied from 0 to 2 V. The measured phase noise at 1-MHz frequency offset is À118.65 dBc/Hz at the oscillation frequency of 7.89 GHz, and the figure of merit of the proposed QVCO is about À185.71 dBc/Hz.

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