A low-power high-linearity voltage controlled oscillator employing unipolar metal oxide thin-film transistors

Abstract

A novel low-power VCO based on Indium-Zinc-Oxide (IZO) thin-film transistors (TFTs) technology is introduced for TFT VCO-based ADCs. A typical ring oscillator (RO) may have poor linearity because the supply voltage controls its frequency. Therefore, a non-inverting frequency control cell (FCC) is integrated into a traditional 7-stage RO (VCO-odd) to improve linearity. Then the FCC is changed to be inverting, and the number of stages is reduced to 6 (VCO-even) to lower power consumption. Experimental results show power consumption of 247.2 $\mu$W and 127.2 $\mu$W, with linearity errors of 2.46% and 2.39%, respectively. Sine waves are applied to verify the VCOs’ conversion functions. Results show that they achieve SNDRs of 40.75 and 40.82 dB. These VCOs show potential for use in low-speed sensor readout interfaces.