An X-Band Low-Phase-Noise Class-F23 VCO Without Manual Harmonic Tuning Based on Switched-Transformer and Wideband Common-Mode Resonance

In this article, a nonmanual harmonic tuning method is introduced for an
${X}$
-band low-phase-noise (PN) Class-F23 voltage-controlled oscillator (VCO). The VCO organically combines two beneficial structures. Switched coils are assembled into a customized transformer-based F3 resonator to achieve coarse frequency tuning with a constant differential-mode (DM) resonance ratio [(
$f {_{H}}/f {_{L}}$
)
$\mathrm {_{DM}}$
= 3]. Besides, top–bottom dual-implicit common-mode (CM) resonators provide staggered poles to expand the second-harmonic impedance, avoiding PN deterioration due to the poisonous harmonic phase. Hence, the optimal flicker and thermal PN over the frequency tuning range (FTR) are maintained without complex manual harmonic tuning and calibration. To save area and power, a current-biased differential common source (CS) buffer reuses the VCO core current and simultaneously uses the DM of the function-reuse bottom resonator to deliver the oscillation signal to the load. The VCO is fabricated in a 110-nm complementary metal–oxide–semiconductor (CMOS) process, and the measured PN at 1 and 10 MHz is
$-115.3\,\,\pm $
1.7 and
$-135.4\,\,\pm $
1.3 dBc/Hz over a 17.5% FTR, respectively, while consuming only 2.7 mW of the VCO core. The figure-of-merit (FoM) shows a fairly small variation over the FTR, which is 192.0 ± 1.1 and 192.6 ± 1.1 dBc/Hz at 1 and 10 MHz, respectively. The measured 1/
$f^{3}$
PN corner is 200–350 kHz.