Analysis and design of a 1.8-GHz CMOS LC quadrature VCO

TLDR

This paper presents a quadrature voltage‑controlled oscillator based on coupling two LC‑tank VCOs. The QVCO is implemented in a 0.35‑µm CMOS process with three metal layers, coupling two LC‑tank VCOs. The QVCO achieves 1.64–1.97 GHz tuning, phase noise ≤ –140 dBc/Hz at 3 MHz offset with 25 mA from 2 V, and an I‑Q phase error ≤ 0.25°, matching theory and simulation in the 1/f³ region.

Abstract

This paper presents a quadrature voltage-controlled oscillator (QVCO) based on the coupling of two LC-tank VCOs. A simplified theoretical analysis for the oscillation frequency and phase noise displayed by the QVCO in the 1/f/sup 3/ region is developed, and good agreement is found between theory and simulation results. A prototype for the QVCO was implemented in a 0.35-/spl mu/m CMOS process with three standard metal layers. The QVCO could be tuned between 1.64 and 1.97 GHz, and showed a phase noise of -140 dBc/Hz or less across the tuning range at a 3-MHz offset frequency from the carrier, for a current consumption of 25 mA from a 2-V power supply. The equivalent phase error between I and Q signals was at most 0.25/spl deg/.