| Abstract: | WiMAX主要為一種提供高頻寬、長距離傳輸的無線寬頻技術。類比/數位轉換器(A/D Converter)在其系統中扮演極其重要的角色。超取樣和 調變技術則是早已被應用於現代超大型積體電路中的類比數位轉換介面。由於超取樣的特性，使得三角積分調變器通常都被限制在音頻信號應用上。隨著超大積體電路製程的改良，使許多的研究逐漸轉移至寬頻帶的應用上，如GSM、WCDMA、Bluetooth、xDSL及WiMAX等。
隨著無線通信的進步，系統上需要做到高速高解析度的類比/數位轉換器需要高取樣率及高階數。在考量低電壓及低功率的條件下，低階三角積分調變器已無法滿足這高頻寬需求，所以高階多位元三角積分調變器在這高頻寬系統是必須的。而未來產品發展導向朝向體積小巧、價格低廉、及較長待機時間發展，因此SOC(System-on-Chip)及低功率消耗設計概念將是未來無線寬頻及行動通訊技術發展之不可或缺的兩個重要因素。
本論文所研究的方向為設計並實現應用於WiMAX寬頻三角積分調變器。為了配合WiMAX系統，電路設計是一個非常大的挑戰。選擇系統架構上，我們選擇超取樣ADC，它擁有適應性、可程式性，以及對類比電路的非理想特性不敏感。而且這項技術還有另外一個優點，它能讓前置的防重疊濾波器規格要求得以減輕。還有它所消耗的功率和雜訊都並不嚴重。在設計考量上，因為類比電路中的積分器會產生許多非理想效應，如有限的直流增益，電容偏差…等等，以及回授路徑上有數位轉類比轉換器(D/A Converter)的非線性效應，這些都會影響我們高階多位元三角積分調變器效能。本論文中，我們將這些非理想效應以Matlab這套軟體來訂定改良出更精準的高階多位元三角積分調變器效能。經由模型來最佳化系統係數及電路規格，以期節省設計的時間。最後利用HSPICE來輔助我們設計模擬出我們所要的電路結果。
本篇論文所提出之應用於WiMAX之寬頻三角積分調變器，在0.18微米1P6M標準製程中實現，工作電壓為1.8V，系統WiMAX頻寬為10MHz，取樣頻率為160MHz，超取樣比為8，模擬結果為取樣頻率160MHz下，其動態範圍為80dB，而最大的訊號雜訊失真比大約為78dB。
WiMAX is a mainly wireless wideband technique for high bandwidth and long distance. The analog-to-digital (A/D) converters play an important role in the system. The over-sampling and noise shaping techniques are applied in analog to digital conversion interface of modern very-large-scaled integrated circuits. Duo to the over-sampling characteristics, delta sigma (ΔΣ) modulators are limited on the application of voice band signals. As the integrated circuits process is improved, it makes many researches transferring to wide-bandwidth applications gradually, such as GSM, WCDMA, Bluetooth, xDSL, and WiMAX.
With the progress of wireless communication, A/D converters need higher oversampling ratio and order to achieve the higher speed and resolution in the system, Duo to the requirements of low voltage and low power consumption, the low order delta sigma modulators are not suitable for the high bandwidth system. So, the high order Multibits delta sigma modulator is necessary in the wideband system. The coming products are expected to integrate for less chip area, low cost, and low power consumption. Therefore, the SOC (System on Chip) and low power consumption are the most important concepts in the development for wireless and modern communication systems.
In this thesis, we design and impletement Wideband Delta Sigma Modulators for WiMAX. For fitting WiMAX system, the circuit design is a great challenge. Our choice is a delta-sigma ADC, because it has great features for adaptability、programmability, and nonsensitivity to analog components such as the device mismatch and amplifier gain. In addition, it has other advantage of relaxing the requirements of the analog anti-aliasing filters in the AD converters. On the other hand, there is no significant power consumption and noise penalty for the AD conversion of the modulator. Furthermore, the circuit non-idealities effects also can be included in our architectures to predict the final performance of actual the ΔΣ modulators. According to these non-idealities models and analyses, we can obtain the optimum circuit specifications to implement our ΔΣ modulator.
In this thesis, Wideband Delta Sigma Modulators for WiMAX is implemented in a standard 0.18-μm 1P6M CMOS technology. The simulation results show that the bandwidth is 10MHz；the sampling frequency is 160MHz；oversampling ratio is 8；the dynamic range and signal to noise distortion ratio are 80 dB and 78 dB |
