Low‐phase‐noise CMOS VCO with harmonically tuned LC tank

A low‐phase‐noise voltage‐controlled oscillator (VCO) has been demonstrated using a harmonically tuned LC resonance tank. In this circuit configuration, the voltage shape at the differential cell is almost rectangular; thus, the cell is switched effectively and the phase noise is reduced. More importantly, the proposed tank suppresses down‐conversion of the noise around 2f 0 to the phase noise, due to the 2 nd harmonic short of the tank. Therefore, the phase noise of the VCO based on the tank is improved considerably. The VCO for 1‐GHz operation has been realized using a 0.35‐μm CMOS process. It shows a phase noise of −111.6 dBc/Hz at 100 KHz offset, which is a 5.7‐dB improvement over a comparable standard VCO. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 164–167, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20240