An Ultra-Wideband VCO Using Digitally Controlled Varactor Arrays in 40-nm CMOS Technology

The paper presents an ultra-wideband and low phase-noise voltage-controlled oscillator (VCO) for 5G applications. To tackle the bandwidth limitation and lossy issue induced by commonly used switched capacitor banks for frequency tuning, the novel method of using digitally controlled varactor arrays is proposed and investigated. Improved phase noise, tuning range, and reduced power consumption are obtained from theoretical analysis and circuit simulations. To validate the design theory, a X-band VCO with 4-bit varactor array is designed and implemented in a 40-nm CMOS technology. The full-wave electromagnetic assisted post-layout simulations show the VCO features a broad tuning range of 8.86-13.4GHz (41%) with only 6 mW DC power consumption from a 1.1V supply. The FoM/FoMT of -185/-197 dBc/Hz are among the state-of-the-art designs.