LC-active VCO for CMOS RF transceivers

A novel fully integrated CMOS LC tank VCO is presented. The LC tanks are implemented by exploiting the active circuit 'boot-strapped inductor' (BSI), which behaves like a high-quality factor inductor. Particularly, the LC tanks have been implemented by introducing a new version of the CMOS BSI circuit, which provides better versatility and design reliability. In order to verify the effectiveness of such an approach, a case study for 5-6GHz direct-conversion multi-standard WLAN transceivers is presented. The VCO has been designed in a 0.35 mu m standard CMOS technology. The new BSI exhibits a high-quality factor (higher than 25 over the all frequency range) and provides a high selectivity without introducing a relevant excess of noise, for a better spectral purity and a lower phase noise (PN) of the VCO. The overall VCO circuit consumes 9 mW. The VCO produces an oscillation in the tuning range from 4.91 to 5.93 GHz (nearly equal to 19%). The circuit exhibits a PN of -129 dBc/Hz at 1 MHz of frequency offset from the central frequency (5.4 GHz) and a FOM equal to 189.5 dBc/Hz at 100 kHz and 194.1 dBc/Hz at 1 MHz of frequency offset, respectively. Copyright (C) 2009 John Wiley & Sons, Ltd.