  Low-power quadrature voltage-controlled oscillator (QVCO) design utilizing
transformer-feedback and current-reuse techniques with increased frequency
range is proposed in this paper. With increasing demand for QVCOs in on-chip
applications, the conventional spiral inductor based approaches for QVCOs has
become a major bottleneck due to their large size. To address this concern, we
propose to replace the conventional spiral inductor based approaches with
through-silicon-via (TSV) inductor based approach in three-dimensional
integrated circuits (3D ICs). In addition, the proposed QVCO circuit can
provide higher frequency range of operation compared with conventional designs.
Experimental results show by replacing conventional spiral transformers with
TSV transformers, up to 3.9x reduction in metal resource consumption. The
proposed QVCOs achieves a phase noise of -114 $dBc/Hz$@1 $MHz$ and -111.2
$dBc/Hz$@1 $MHz$ at the carrier of 2.5 $GHz$ for toroidal TSV transformed
based-QVCO and vertical spiral transformer based-QVCO respectively. The power
consumption is only 1.5 $mW$ and 1.7 $mW$ for toroidal TSV transformed
based-QVCO and vertical spiral transformer based-QVCO respectively, under the
supply voltage of 0.7 $V$.
