Fully Differential 5-GHz LC-Tank VCOs with Improved Phase Noise and Wide Tuning Range

• Published in: ETRI journal Vol. 27; no. 5; pp. 473 - 483
• Main Authors: Lee, Ja-Yol, Park, Chan-Woo, Lee, Sang-Heung, Kang, Jin-Young, Oh, Seung-Hyeub
• Format: Journal Article
• Language: Korean
• Published: 한국전자통신연구원 01.10.2005; ETRI
• Subjects: 전자/정보통신공학; VCO; flicker noise; phase noise; LC-tank; CCNF
• ISSN: 1225-6463; 2233-7326

In this paper, we propose two LC voltage-controlled oscillators (VCOs) that improve both phase noise and tuning range. With both 1/f induced low-frequency noise and low-frequency thermal noise around DC or around harmonics suppressed significantly by the employment of a current-current negative feedback (CCNF) loop, the phase noise in the CCNF LC VCO has been improved by about 10 dB at 6 MHz offset compared to the conventional LC VCO. The phase noise of the CCNF VCO was measured as -112 dBc/Hz at 6 MHz offset from 5.5 GHz carrier frequency. Also, we present a bandwidth-enhanced LC VCO whose tuning range has been increased about 250 % by connecting the varactor to the bases of the cross-coupled pair. The phase noise of the bandwidth-enhanced LC-tank VCO has been improved by about 6 dB at 6 MHz offset compared to the conventional LC VCO. The phase noise reduction has been achieved because the DC-decoupling capacitor Cc prevents the output common-mode level from modulating the varactor bias point, and the signal power increases in the LC-tank resonator. The bandwidth-enhanced LC VCO represents a 12 % bandwidth and phase noise of -108 dBc/Hz at 6 MHz offset.