Concurrent VCO using capacitive coupled oscillators

This letter proposes a new concurrent CMOS voltage-controlled oscillator (VCO). The oscillator consists of two sub-VCO operates at 4 GHz and 6 GHz respectively. The two sub-VCOs are coupled by a pair of MIM capacitors. The proposed oscillator has been implemented with the TSMC 0.18 μm BiCMOS technology. By controlling the supply voltages, the VCO has three different operational modes, capable of generating a single frequency in either the 4- or 6-GHz band as well as two frequencies in the 4- and 6-GHz bands simultaneously. In the concurrent mode, the VCO can generate differential signals at 4 GHz, 6 GHz and their harmonics and other cross-modulation products. The measured phase noise at 1-MHz offset frequency is -111.99 and -121.75 dBc/Hz when the oscillator oscillates at a single frequency of 6.24 or 4.03 GHz, respectively. The phase noise is -113.41 and -108.94 dBc/Hz, respectively, when the oscillator oscillates at 3.97 and 6.64 GHz simultaneously. The die area of the concurrent oscillator is 1.178×0.583 mm
²
.