A wide-band low phase noise LC-tuned VCO with constant K-VCO/omega(osc) for LTE PLL

A wideband LC-tuned voltage-controlled oscillator (LC-VCO) applied in LTE PLL frequency synthesizers with constant K-VCO/omega(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 = partial derivative C-var/partial derivative 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-mu m RF-CMOS process. The VCO exhibits a maximum variation of K-VCO/omega(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.