A Compact TF-based LC-VCO with Ultra-Low-Power Operation and Supply Pushing Reduction for IoT Applications

Abstract

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 -114.8 dBc/Hz at 1MHz frequency offset and 16 kHz flicker corner with a 103 μWpower consumption at 2.6 GHz oscillation frequency, which corresponds to a -193 dBc/Hz VCO figure-of-merit (FoM) and only occupies 0.12mm² on-chip area. The supply pushing is reduced to 2 MHz/V resulting in a -50 dBc spur, while 5MHz sinusoidal ripples with 50mV_PP are added on the DC supply.