Sub-1V V-I converter-based voltage-controlled oscillator with a linear gain characteristic

Abstract

This letter proposes a novel sub-1V voltage-current (V-I) converter- based voltage-controlled oscillator (VCO) for the low-voltage phaselocked loop (PLL) of display driver integrated circuit. The proposed VCO improves on the state-of-the-art V-I converter-based VCO, which uses a firstorder current equation for the VCO, to achieve linear voltage-to-frequency gain of the VCO (K-VCO) over the full range of the control voltage, from the ground to the supply voltage in sub-1V CMOS technology. To obtain a full supply transition output with high immunity to noise, the improved VCO is designed to control the gate voltage of a metal-oxide-semiconductor fieldeffect transistor (MOSFET), instead of the supply voltage of a ring oscillator without significant area overhead. As a result, the proposed VCO obtains a linear KVCO with a wider control voltage range than a conventional VCO when its tuning range is from 1.25 to 3.6 GHz in a 65 nm 1.0V CMOS technology.