Work

Low-Power Class-C VCO in SiGe BiCMOS With Varactor Embedded in Cross-Feedback Path for Tuning Range Enhancement

Year: 2025

Type: article

Abstract: The tuning range (TR) ofLCvoltage-controlled oscillators (VCOs) is primarily limited by the maximum tuning ratio of varactors in a given process, and significantly degraded by parasitic capacitance of the transistors in a cross-feedback path especially for millimeter-wave (mm-wave) VCOs. In this article, a mm-wave class-C VCO is demonstrated in silicon-germanium (SiGe) bipolar complementary metal-oxide–semiconductor (BiCMOS) technology, with varactors embedded in the cross-feedback path to enhance the TR. Equivalent circuit model and derived analytical expressions show that in the presence of large parasitic capacitance at the base of the transistors, introducing varactors in the cross-feedback path significantly improves the overall TR. Therefore, the TR limitation by varactor tuning ratio can be released. Analysis of start-up and phase noise with consideration of base parasitics and practical values of cross-feedback capacitance are given to replenish the conventional class-C analysis and methodology. Based on the analysis, a VCO containing varactors both in theLC-tank and the cross-feedback path is proposed to achieve a continuous TR from 29.6 to 32.4 GHz, low dc power consumption of 10.1 mW, and low-phase noise of$-114.6~\text {dBc/Hz}$at 10-MHz offset in measurements.

Source: IEEE Transactions on Microwave Theory and Techniques

DOI: 10.1109/tmtt.2025.3567766

Authors: Xun Chen, Jonas Winkelhake, Muh-Dey Wei, Renato Negra

Institution: RWTH Aachen University

Language: English

Topic: Radio Frequency Integrated Circuit Design

Subfield: Electrical and Electronic Engineering

Field: Engineering

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $2,645

Funder: Ministry of Education and Research, Romania