摘要

近年來，由於無線通訊系統快速地發展，通訊系統中的高頻積體電路的要求越來越嚴格。其中頻率合成器在通訊IC扮演極重要的腳色，而在頻率合成器中，壓控振盪器(VCO)是一個很重要的區塊。在此論文中，主要討論如何設計一個低相位雜訊且寬頻的VCO，而基底雜訊耦合對VCO的影響也被討論。
本論文一開始介紹VCO的原理，VCO的設計考量並且介紹兩種相位雜訊的模型。接下來介紹兩種寬頻且低雜訊的VCO架構，此二種架構分別利用差動調整可變電容(differentially tuned varactors)和電容陣列與開關(capacirots arry and switches)來降低相位雜訊。此二VCO都是以TSMC 0.18um CMOS製程製作。輸出頻率從3GHz到5GHz，而在距離載波1MHz處的相位雜訊表現為-113dBc/Hz。
近年來因為將數位與類比電路整合在一個晶片上的趨勢，基底雜訊也越來越被重視。本論文研究基底雜訊對VCO的影響，包含了雜訊經由數種不同的pad輸入對VCO輸出的影響之比較。另外，電感的guard ring接地或浮空對VCO的影響也在本論文中比較與討論。在本文中證明了接地的(grounded)電感guard ring提供了一個比浮空的(floated)電感guard ring高9.4dB的基底雜訊免疫度。

Abstract

In recent years, due to the rapid development of the wireless communication systems, the specifications of the RF integrated circuits inside these systems become very rigorous. The frequency synthesizer plays a very important role in various communication ICs, in which the voltage controlled oscillator (VCO) is the key component for high performance frequency synthesizer. In this study, the main focus is about design of low phase noise and wide band VCO. The substrate noise coupling effect in VCO is also discussed.
This thesis first introduces the fundamentals of VCO such as the design considerations of VCO and the modeling of the phase noise in a VCO. Next describes two wide band and low phase noise VCO structures, which can reduce phase noise by the differentially tuned varactors and the capacitors array and switches, respectively. Both these two VCOs are fabricated by TSMC 0.18□m CMOS process. The output frequency is from 3GHz to 5GHz, and the phase noise at 1MHz offset is -113dBc/Hz.
Due to the trend of integrating the digital circuits and analog circuits on a single chip in recent years, substrate noise is being taken more and more seriously. This thesis investigates the effect of substrate noise on VCO, including the comparison of the VCO output performances with the noise injected via several different pads. Furthermore, the effect of the inductor grounded or floated on the VCO is compared and discussed in this thesis also. It is demonstrated the grounded inductor guard ring provides a better isolation from substrate noise than the floated one by 9.4dB.

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