A Compact Low Power Active Oscillator Using Oxide TFTs on a Flexible Foil

This letter presents a novel voltage-controlled LC oscillator (LCO) designed for energy-efficient wearable applications. The circuit employs a compact AIND topology paired with cross-coupled transistors to generate sustained oscillations. The active inductor (AIND) has been implemented with four transistors. Cross-coupled transistors provide negative resistance to circumvent losses due to parasitic resistance, enabling robust oscillation while minimizing area. This LCO is fabricated on a 27μm thick flexible polyimide substrate using all enhancement n-type amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) technology. From measurements, the LCO has shown a wide tuning range (power consumption) of 152 kHz (10.4μW) to 1.9MHz (450μW), when the supply voltage (VDD) is swept from 0.8V to 2.5V, respectively. Moreover, the LCO exhibits a phase noise of -94.26dBc/Hz and -90dBc/Hz at a offset frequency of 10 kHz at a VDD of 2V and 0.8V respectively. The average tuning sensitivity (KLCO) is around 985 kHz/V. Reproducibility and stress dependent stability of the LCO has been validated from multiple sample’s experimental characterization. This circuit occupies a total active area of 0.03mm. These parameters indicate that the proposed LCO can find potential applications in on-chip clock generation to implement compact wearable devices.