This paper presents a miniaturized transformer-based ultra-low-power (ULP) LC-VCO with embedded supply pushing reduction techniques for IoT applications in 65-nm CMOS process. To reduce the on-chip area, a compact transformer patterned ground shield (PGS) is implemented. The transistors with switchable capacitor banks and associated components are placed underneath the transformer, which further shrinking the on-chip area. To lower the power consumption of VCO, a gm-stacked LC-VCO using the transformer embedded with PGS is proposed. The transformer is designed to provide large inductance to obtain a robust start-up within limited power consumption. Avoiding implementing an off/on-chip Low-dropout regulator (LDO) which requires additional voltage headroom, a low-power supply pushing reduction feedback loop is integrated to mitigate the current variation and thus the oscillation amplitude and frequency can be stabilized. The proposed ULP TF-based LC-VCO achieves phase noise of -114.8dBc/Hz at 1MHz frequency offset and 16kHz flicker corner with a 103µW power consumption at 2.6GHz oscillation frequency, which corresponds to a -193dBc/Hz VCO figure-of-merit (FoM) and only occupies 0.12mm2 on-chip area. The supply pushing is reduced to 2MHz/V resulting in a -50dBc spur, while 5MHz sinusoidal ripples with 50mVPP are added on the DC supply.

In this paper, several spiral inductors with various ground clearance structures and turns were investigated to achieve noise suppression up to the fourth harmonic (3.2 GHz) regime of DDR3-1600. Their performances were characterized in terms of their capability to effectively suppress simultaneous switching noise (SSN) in the frequency region of interest. For a wider noise suppression bandwidth, a spiral inductor with large ground clearance, which provides a high self resonance frequency (SRF) as well as high inductances, was implemented. The proposed spiral inductor exhibited good noise suppression characteristics in the frequency domain and achieved 50% voltage fluctuation reduction in the time domain, compared to the identical 4-turn spiral without pattern ground structure.