A X-Band Capacitor-Coupled QVCO Using Sinusoidal Current Bias Technique

I-Shing Shen*, Christina Jou

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


This study introduces an X-band quadrature voltage-controlled oscillator (QVCO) based on two novel techniques: capacitor coupling and sinusoidal current biasing. The proposed QVCO achieves an excellent figure-of-merit (FOM) of 190.5 dBc/Hz. This study analyzes the properties of this QVCO, including its phase noise, oscillation frequency, and amplitude. To generate quadrature phase signals with low phase noise, the proposed design uses two capacitor-coupled LC-tank cores instead of active device-coupled cores. Sinusoidal currents through these capacitors bias the oscillator, increasing oscillation amplitude and reducing the phase noise contribution from cross-coupled transistors compared to existing QVCOs or VCOs biased with a constant current. These two techniques allow the proposed QVCO to achieve at least a theoretical 3 dB phase noise improvement compared to conventional LC-QVCOs. Implemented in a standard 0.18 mu m CMOS process, the proposed QVCO had a frequency tuning range of 9.2 similar to 10.4 GHz and a phase noise of -115.7 dBc/Hz@1 MHz from a carrier of 10.4 GHz while consuming 3.6 mW with 1.5 V voltage supply.
Original languageEnglish
Pages (from-to)318-328
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number2
StatePublished - Feb 2012


  • Quadrature voltage-controlled oscillator (QVCO); sinusoidal bias technique; capacitor-coupled; phase noise; oscillation amplitude

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