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

Abstract

This letter presents a novel voltage-controlled LC oscillators (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 $27~ \mu $ m 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 ( $10.4~ \mu $ W)–1.9 MHz ( $450~ \mu $ W), when the supply voltage (VDD) is swept from 0.8 to 2.5 V, respectively. Moreover, the LCO exhibits a phase noise of –94.26 and –90 dBc/Hz at a offset frequency of 10 kHz at a VDD of 2 and 0.8 V, respectively. The average tuning sensitivity $(K_{\text {LCO}})$ 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 0.03 mm2. These parameters indicate that the proposed LCO can find potential applications in on-chip clock generation to implement compact wearable devices.