射頻CMOS雜訊數值模擬

Abstract

由於無線通訊的蓬勃發展，射頻積體電路的需求日益增長，目前主要的射頻電路大多採用砷化鎵或是雙載子矽基底為主體的技術來實現，此乃因為這兩類的元件有著極高的電流截止頻率；然而，隨著金氧半場效電晶體的製程技術提昇與元件設計能力的進步，元件尺寸逐漸縮小，短小的通道長度使得元件的電流截止頻率大大的提昇，因此，在射頻的應用範圍內，其已足以與傳統高速元件相互比擬。但是，射頻電路的設計元件迄今並未大量採用製程技術成熟與成本相對較低的互補式金氧半元件，歸因於其缺乏精準的高頻等效電路模型，尤以元件的高頻雜訊與功率增益模型為最，使得電路設計者無以為藉。 本篇即以探究元件的高頻雜訊指數為主，並非著手建立一套精確的雜訊模型，而是利用數值模擬，從原始的雜訊來源出發，在所有可能貢獻雜訊之處，計算出其量之大小，並將其反應於元件之終端埠的分量分別求出，最後彙集在一起，即是元件終端埠所產生的雜訊之量的大小，過程當中，一項運用y 參數的小訊號分析概念來求取分量大小的方法於此提出。最後，值得一提的是，本篇的模擬皆是於TMA公司的二維元件模擬軟體 Medici上完成的，也因為整個數值方法是從雜訊的最初來源作為模擬的出發點，因此提供了對雜訊較為深入的理解同時亦展現出雜訊在元件中的原貌。

Due to great flourish of wireless communications, radio-frequency integrated circuits (RF IC’s) are becoming more in demand. The majority of RF IC’s are typically implemented in GaAs or silicon bipolar technologies because of their relative-ly high unity current gain cutoff frequency. Comparably, with the progress in process technology and device design of the MOS transistors, the continuing scaling down of the minimum channel length has given rise to the increasing cutoff frequency. As a consequence, the CMOS devices start to emerge in the components of RF IC’s. However, the implementation that takes full advan-tage of the RF performance of the CMOS transistors is still a challenging task. The major barrier to realization of commer-cial RF CMOS components is the lack of adequate models, parti-cularly the noise model, which accurately predict the device behavior at high frequencies. The main concern for this work will focus on the derivation of noise within MOS devices. Rather than constructing an analy-tical noise model, the simulation task is performed directly through numerical calculation. The adopted method inherently takes into account all the microscopic noise sources within the transistors at radio frequencies. A by-product, so-called the Green’s function, is evaluated through an innovative techni-que, i.e. associated with the concept of y-parameter under AC small-signal analysis. Since the noise model of MOS devices is inadequate at high frequency, the numerical simulation will be able to achieve a far better insight on the nature and the ori-gin of noise for the devices. It should be declared that the thorough simulation task is implemented into the framework of 2D device simulator TMA Medici.