A wideband LC-tuned voltage-controlled oscillator (LC-VCO) applied in LTE PLL frequency synthesizers with constant KVCO/ωosc 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 Vtune or VDD.The switches are controlled by switching bits.With this scheme,the ratio of KV =(6)Cvar/(6)Vtune 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 KVCO/ωosc 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.
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