题目/Title：Class-C VCO的设计
                        A Class-C VCO Based Σ-Δ Fraction-N Frequency Synthesizer with AFC for 802.11ah Applications

作者/Author：俞小宝,韩思杨,靳宗明,王志华,池保勇
                        Xiaobao Yu,Siyang Han,Zongming Jin,Zhihua Wang,Baoyong Chi

期刊/Journal：半导体学报 Journal of Semiconductors

年份/Issue Date：2015

卷（期）及页码/Volume（No.）&pages：Vol.36, No.9

摘要/Abstract：

A 1.4-2GHz phase-locked loop (PLL) Σ-Δ fraction-N frequency synthesizer with automatic frequency control (AFC) for 802.11ah applications is presented. A Class-C voltage control oscillator (VCO) ranging from 1.4GHz to 2GHz is integrated on-chip to save the power for the Sub-GHz band. Besides, a novel AFC algorithm is introduced to maintain the VCO oscillation at the start-up and automatically search for the appropriate control word of the switched-capacitor array to extend the PLL tuning range. A 20-bit third-order Σ-Δ modulator is utilized to reduce the fraction spurs while achieving the frequency resolution less than 30Hz. The measurement results show that the frequency synthesizer has achieved a phase noise of <-120dBc/Hz at 1MHz offset and consumes 11.1mW from a 1.7V supply. Moreover, compared with the traditional Class-A counterparts, the phase noise in Class-C mode has been improved by 5dB under the same power consumption.