A 3.7-mW K-Band Dual-Feedbacks VCO Employing a Self-Inversed Transformer With 190-dBc/Hz FOM

In this letter, a novel
$K$
-band dual-feedbacks (DFs) voltage-controlled oscillator (VCO) is implemented. The DF structure combines both drain-to-gate (D2G) and source-to-gate (S2G) feedback approaches to eliminate the time of triode working region. To satisfy the inversed directions in two feedbacks, we design a self-inversed transformer to realize opposite coupling. The layout is highly compact and coupling mechanisms are analyzed to guide design optimization. Measurement results suggest the prototype implemented in 55 nm CMOS only consumes 3.7 mW of power while occupying core area of 0.046 mm2. The phase noise (PN) is around −108.45 dBc/Hz at 23.1 GHz (offset 1 MHz) and the tuning range is around 4%. Calculated FOM and FOMA can reach 190 and 203.4 dBc/Hz, respectively.