This paper presents a K-band CMOS cross-coupled pair voltage-controlled oscillator (VCO) that utilizes the varactor-only capacitor network. The proposed circuit features low parasitics and a compact capacitor network, such that the varactor in the analog tuning path directly affects the oscillation frequency with a large gain of the VCO, and the varactor in the digital tuning path results in minimal noise sources, thus achieving low phase noise for the automotive FMCW radar application. This VCO was designed using TSMC 65 nm technology, and the post-layout simulation results show a stable oscillation across 18–19.2 GHz, a minimum phase noise of −105.9 and −128 dBc/Hz at 1- and 10-MHz offset frequencies while dissipating 21 mW of power from a 1 V supply. Furthermore, no notable variations in phase noise are observed across the oscillation frequency tuning range. It reveals a figure of merit (FOM) of −178.3 dBc/Hz while using a varactor-only capacitor array and occupying a small chip area.

This paper presents a current-reused coupled oscillator with improved noise circulating technique for phase noise improvement. The proposed current-reused coupled oscillator with order of 2, where the noise circulation oscillator is stacked on top of PMOS cross-coupled oscillator solves the strict trade-off between power consumption and phase noise. The degeneration transistors for noise circulating operations are biased in triode-region instead of in saturation to provide an optimum delay in loop gain, such that the positive and negative phase change in the normalized impulse sensitivity function (ISF) become more symmetric. Thus, the 1/f³ phase noise is significantly improved. The voltage-controlled oscillator (VCO) was implemented using CMOS 65nm technology, and the measurement results demonstrated its operation within a frequency range of 15.4–17 GHz (9.8% tuning range). Despite its low power dissipation of 6.3 mW, the VCO design exhibits excellent performance, offering a phase noise of -111.2 dBc/Hz at 1 MHz offset frequency. Furthermore, the proposed VCO attains a figure of merit (FoM) of -187.4 dBc/Hz.

A harmonic cancellation technique based on a phase manipulation technique is presented for Ku-band voltage-controlled oscillators (VCO), achieving significant phase noise reduction, especially at the $1/f^{3}$ region. The proposed VCO incorporates an auxiliary PMOS transistor with dynamically controlled biasing to generate additional high-order components to compensate for the intrinsic phase difference between the high-order harmonic components of the main PMOS and NMOS cross-coupled transistors, establishing the required $180^{o}$ phase difference ( $\Delta \theta $ ) between them. The alignment, facilitated by the proposed technique, significantly suppresses the undesired high-order harmonic components entering the tank’s capacitive path and disturbing its natural frequency. The proposed VCO is fabricated in 65nm CMOS technology, achieving a phase noise of −33.78 dBc/Hz at 1 kHz and -112 dBc/Hz at 1 MHz. The phase noise improvement reaches 5.56 dB at the $1/f^{3}$ region compared to a conventional complementary VCO. With a low power consumption of 4.5 mW, the proposed VCO achieves an excellent figure-of-merit (FoM) of −188.4 dBc/Hz with a tuning range of 1.1 GHz (8.1%) operating from 13 GHz to 14.1 GHz.

The miniaturization of dielectric sensing has driven the development of both oscillator- and receiver-based sensors. Wide-frequency-range and low-power-consumption voltage-controlled oscillators (VCOs) are required as a reference clock for receiver-based dielectric spectroscopy. In this paper, we propose a switched coupled inductor VCO offering sufficiently wide bandwidth in a power-efficient manner. The proposed switched coupled inductor offers higher coupling factor and mutual inductance compared to direct switched inductor schemes along with a higher quality factor and tuning range. The proposed switched coupled inductor improved the frequency tuning range by 21% compared to the conventional VCO. The measurement results show that the proposed VCO oscillates from 4.7 to 8.8 GHz frequency, suitable for dielectric spectroscopy sensors. With only 4.5 mW power consumption, the proposed VCO can achieve −103.3 dBc/Hz phase noise at 1 MHz offset, with a resulting tuning range figure-of-merit (FOM_T) of −187.4 dBc/Hz.