Low Supply Voltage Control Oscillator with Transformer Feedback for Photoplethysmography

An ultra-low supply voltage differential voltage controlled oscillator (VCO) is designed and implemented using TSMC SiGe 0.18µm CMOS 3P6M process for biomedical application and photoplethysmography. The designed circuit topology is an native nMOS-core cross-coupled LC-tank VCO and extremely-low-voltage and low power operation is achieved using on-chip transformers in positive feedback loops to swing the output signals above the supply and below the ground potential. At the supply voltage of 0.2 V, the output phase noise of the VCO is −117.63 dBc/Hz at 1MHz offset frequency from the carrier frequency of 991MHz, and the figure of merit is − 180.2 dBc/Hz. Total power consumption is 0.536mW. Tuning range is about 111MHz, from 991 to 1102MHz, while the control voltage was tuned from 0 V to 2 V. The die area is 0.472 × 0.722 mm2.