Title page for ETD etd-05072001-094836

Type of Document Master's Thesis
Author Bunch, Ryan Lee
Author's Email Address rbunch@vt.edu
URN etd-05072001-094836
Title A Fully Monolithic 2.5 GHz LC Voltage Controlled Oscillator in 0.35 um CMOS Technology
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Raman, Sanjay Committee Chair
Athanas, Peter M. Committee Member
Bostian, Charles W. Committee Member
  • VCO
  • resonator
  • RFIC
  • oscillator
  • integrated circuit
  • inductor
  • varactor
  • nonlinear
  • CMOS
Date of Defense 2001-04-26
Availability unrestricted
The explosive growth in wireless communications has led to an increased

demand for wireless products that are cheaper, smaller, and lower

power. Recently there has been an increased interest in using CMOS, a

traditional digital and low frequency analog IC technology, to implement

RF components such as mixers, voltage controlled oscillators (VCOs), and

low noise amplifiers (LNAs). Future mass-market RF links, such as

BlueTooth, will require the potentially low-cost single-chip solutions

that CMOS can provide. In order for such single-chip solutions to be

realized, RF circuits must be designed that can operate in the presence

of noisy digital circuitry. The voltage controlled oscillator (VCO), an

important building block for RF systems, is particularly sensitive when

exposed to an electrically noisy environment. In addition, CMOS

implementations of VCOs have been hampered by the lack of high-quality

integrated inductors.

This thesis focuses on the design of a fully integrated 2.5 GHz LC CMOS

VCO. The circuit is intended as a vehicle for future mixed RF/digital

noise characterization. The circuit was implemented in a 0.35 um single

poly, 4 metal, 3.3 V, CMOS process available through MOSIS. The

oscillator uses a complementary negative transconductance topology.

This oscillator circuit is analyzed as a negative-resistance

oscillator. Monolithic inductors are designed using full-wave

electromagnetic field solver software. The design of an

"inversion-mode" MOS (I-MOS) tuning varactor is presented, along with a

discussion of the effects of varactor nonlinearity on VCO performance.

I-MOS varactors are shown to have substantially improved tuning range

(and tuning curve linearity) over conventional MOS varactors. Practical

issues pertaining to CMOS VCO circuit design, layout, and testing are

also discussed. The characterization of the VCO and the integrated

passives is presented. The VCO achieves a best-case phase noise of

-106.7 dBc/Hz at 100 kHz offset from a center frequency of 2.73 GHz. The

tuning range is 425 MHz (17%). The circuit consumes 9 mA from a 3.3 V

supply. This represents excellent performance for CMOS oscillator

designs reported at this frequency. Finally, several recommendations for

improvements in oscillator performance and characterization are


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