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

Abstract

This letter proposes a novel sub-1 V voltage-current (V-I) converter-based voltage-controlled oscillator (VCO) for the low-voltage phase-locked 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 first-order 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-1 V 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 field-effect transistor (MOSFET), instead of the supply voltage of a ring oscillator without significant area overhead. As a result, the proposed VCO obtains a linear K_VCO 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 1.0 V CMOS technology.