康香英　徐卫林

摘 要:针对目前通信系统应用上对压控振荡器的片上集成、宽调谐、调幅、启动特性和功耗等提出的综合性要求,分析和设计了一种压控调频调幅振荡器,其延迟单元采用全差分结构,以消除共模噪声和增加延迟控制的灵活性;并利用交叉耦合的差分负阻和电流折叠的正反馈技术进行频率调谐,使之在宽频范围内具有常数振荡幅度。采用0.5 μm CMOS工艺进行Spice仿真,结果表明振荡器具有34~197 MHz的宽调谐范围,并能保持常数振荡幅度,功耗仅10 mW,启动时间仅52 ns。系统还能在0.5~2.0 V范围内进行良好的线性调幅。

关键词:电流折叠;负阻交叉耦合晶体管对;自动振幅控制;全差分压控振荡器

中图分类号:TN402文献标识码:B

文章编号:1004-373X(2009)10-011-02

Design of CMOS Full Differential VCO Based on Current Fold Technique

KANG Xiangying1,XU Weilin2

(1.Xianggang Yixing Refractory Co.Ltd.,Xiangtan,411102,China;

2.Institute of Microelectronics and Information Technology,Wuhan University,Wuhan,430072,China)

Abstract:On-chip VCO with comprehensive target,such as wide tuning,amplitude adjusting,good start up time and lower power,is required in current communication system.A frequency and amplitude adjusting VCO is designed and analyzed.Full differential configuration is used to avoid common mode noise and achieve controlling flexibility of delay cells.Negative resistance differential complementary cross-coupled pair and regenerative feedback technique with current fold are applied to adjust frequency with constant amplitude in large range.Under 0.5 μm CMOS process,Simulation results in SPICE indicate that the VCO proposed behaves in wide linear tuning between 34~197 MHz with constant amplitude,10 mW power dissipation and 52 ns start up time.It also has good linear amplitude adjusting between 0.5~2.0 V.

Keywords:current fold;negative resistance complementary cross-coupled pair;automatic amplitude control;fully differential VCO

射频振荡器是仪器仪表、自动控制和通信系统等领域广泛使用的基本模块,是构成时钟恢复、频率合成等系统的核心电路[1,2]。通常用无源元件LC,隧道二极管、双基极二极管(单结晶体管)、雪崩双极型晶体管来设计,但它们都与标准的CMOS工艺不兼容[3]。虽然LC振荡器有良好的稳定性和相位噪声性能,振荡频率可达微波L带至C带,但调谐范围不大,而且不易于在当前主流CMOS工艺下进行片上集成。因而采用电流折叠的正反馈技术设计了一个全差分CMOS环形压控振荡器(VCO)。该振荡器在调谐时具有常数振荡幅度,并具有良好的线性调频调幅性能。

1 振荡器的工作原理及其全差分实现

1.1 振荡器的工作原理

振荡器是一种不需要外部信号激励,能够将自身的直流能源转换为周期性输出信号的电路。……