Novel VCO Architecture Using Series Above-IC FBAR and Parallel LC Resonance

Abstract

A quasi-monolithic voltage-tunable film bulk acoustic resonator (FBAR) enhanced oscillator for 2.1 GHz in 0.25- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhbox m$</tex> SiGe BiCMOS technology is designed, fabricated, and evaluated. The narrow-band FBAR was built above the SiGe circuit through later Si post-processing steps. The oscillator is based on a two-transistor loop structure and uses two resonators, namely a parallel LC tank and an above-IC FBAR in its series-resonant mode. The improvement in phase noise performance is significant compared to a similar reference LC voltage-controlled oscillator (VCO), with the best phase noise being <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$- hbox144.1~dBc/Hz$</tex> at an offset of 1 MHz and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$- hbox149.6~dBc/Hz$</tex> at 3 MHz. The architecture offers advantages in overcoming frequency tuning difficulties usually present when using high- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex> resonators. Although the width of the tuning range comes at some cost on phase noise, the measured performance satisfies contemporary wireless standards such as GPS.