A new low-phase noise direct-coupled CMOS LC-QVCO

A new LC quadrature voltage-controlled oscillator (LCQVCO), made with direct coupling of two CMOS LC-VCOs, is presented. In the proposed circuit two identical cross-connected LC-VCOs are coupled together by directly connecting the bulk of the crossconnected transistors of one VCO to the bulk of the MOS varactors of the other VCO in such a way no extra devices are needed for coupling. Thus, no extra noise sources and power consumption are added to the core VCOs and results in high performance of QVCO. A Linear analysis of the circuit and the result of simulation in a 0.18μm CMOS technology are presented. The same proposed coupling scheme can be used for multiphase signal generation as well. Simulation shows the proposed QVCO can operate with supply voltage as low as 0.5V .