This paper presents a quadrature VCO (QVCO) that employs gate-to-drain transformers to couple two fundamental oscillators to generate accurate quadrature phases and switched coupled inductors for tuning extension. Thanks to these techniques, it is possible to cover two bands with a single quadrature VCO, without jeopardizing phase noise or demanding extensive silicon area. The oscillator, realized in 28nm HPM bulk CMOS, occupies a core area of only 0.031mm2 and is tunable from 71-to-76GHz and 85.6-to-90.7GHz, resulting in a total tuning range of 9.8GHz. Thepeak phase noise at 10MHz offset from the carrier is -117.7dBc/Hz in the lower band and -110dBc/Hz in the higherone and varies less than 3.5dB within each sub-band. The maximum phase error is 1.5° and 3.5° in the lower and higher band respectively.
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