A　wideband　LC-tuned　voltage-controlled　oscillator　(LC-VCO)　applied　in　LTE　PLL　frequency　synthesizers　with　constant　K　VCO/ω　osc　is　described.　In　order　to　minimize　the　loop　bandwidth　variations　of　PLL,　a　varactor　array　is　proposed,　which　consists　of　a　series　of　differential　variable　capacitor　pairs　and　a　series　of　single-pole　double-throw　(SPDT)　switches　to　connect　V　tune　or　V　DD.　The　switches　are　controlled　by　switching　bits.　With　this　scheme,　the　ratio　of　K　V　=　∂C　var/∂V　tune　and　the　capacitance　value　of　the　capacitor　array　maintains　relatively　constant;　furthermore,　the　loop　bandwidth　of　the　PLL　fluctuation　is　suppressed.　The　3.2-4.6-GHz　VCO　for　multi-band　LTE　PLL　is　fabricated　in　a　0.13-μm　RF-CMOS　process.　The　VCO　exhibits　a　maximum　variation　of　K　VCO/ω　osc　of　only　4%.　The　VCO　also　exhibits　a　low　phase-noise　of-124　dBc/Hz　at　a　1-MHz　offset　frequency　and　a　low　current　consumption　of　18.0　mA　with　a　1.2-V　power　supply.　©　2012　Chinese　Institute　of　Electronics.