快速鎖定的全數位延遲鎖相迴路使用不對稱映射尋跡設計

Abstract

時脈訊號的失真和延遲在不斷變快的IC電路設計中已經變成一個非常重要的考量因素，本論文的目的是設計一個全數位控制的延遲鎖相迴路可以操作在266MHz到800MHz，並且擁有快速鎖定的能力大約十個時脈週期。這個全數位的延遲鎖相迴路採用一個全新的設計方式叫做不對稱映射尋跡，主要用於偵測相位差以及處理相位補償的功能。 本論文所提出的全數位延遲鎖相迴路使用不對稱映射尋跡設計主要由以下五個部分組成： 一、相位差產生電路：此電路用於接受迴授的時脈訊號，然後產生32階線性的相位差訊號，訊號間彼此相隔約100ps。 二、取樣電路及正緣解碼電路： 取樣電路以標準的時脈作為取樣的基準，紀錄標準的時脈和32階延遲時脈的關係，然後將此資料用於正緣解碼電路，判斷出正緣訊號出現的階數位置。 三、相位補償解碼電路：此部分承接第二部分的訊號，先經由優先權解碼電路，將最短和最適合之補償階數找出，設定最高優先權，然後將訊號送至相位補償解碼器，把相位階數轉為5bits的數位控制訊號。 四、5 bits 數位控制線性延遲電路：這個電路接收到相位補償解碼器訊號之後，會根據訊號改變輸入輸出之間的延遲路徑，進而改變時脈的延遲達到相位補償的目的 五、除頻及系統控制電路：除頻器製造出此系統的操作週期，而系統控制電路主要是相位鎖定判斷器，如果鎖定訊號確定，則除頻訊號將不會通過判斷器進而改變輸出延遲的補償值。 此篇論文所提出的方法可以成功的縮短鎖定的所需週期，而且不對稱映射尋跡可以有效的排除IC製程及其他外界因素的影響。

Clock skew is an increasing concern for high speed circuit designing. This paper describes a simple concept for realizing a fast all digital delay locked loop (ADDLL) circuit that operates at high frequency between 300Mhz and 800MHz and with fast lock time about 10 cycles. This ADDLL Circuit adopts a search method, called Asynchronous Time Mapping Tracking (ATMT), to detect and get the information of the phase error between the input and output clock and furthermore tune the output delay path for phase compensation. The ADDLL circuits designed in the paper are consisted of five primary parts : A. Feedback clock phase error generator : This part of the ADDLL system connected with feedback clock and generates 32 phase error outputs which has about 100ps between each other. B. Time sampling and positive edge detector : The 32 phase error outputs feed through this part and the circuit would use the positive edge of the reference clock to sample the state of each phase error. C. Phase error compensation decoder : After the phase error between the feedback clock and reference clock have been quantified , the decoder transfers the decimal data to 5 bits binary form used to control the delay line. D. 5 bits digital controlled delay line : The binary data of the compensation decoder connected with the control ports of this delay line to determine how much the delay time have to been inserted between reference and feedback clock to synchronize the clock. E. Frequency divider and system controller : The system controller is based on a phase detector(PD) has two major function, determining the data capture signal of digital delay line provided by frequency divider, and detecting the phase lock situation of the system to switch the modes of the ADDLL system. The new methodology of the ADDLL system designing in this paper successfully shortens the locked cycles of the circuit and eliminates the affection of interconnect manufacturing variations with wire RC loading affects timing performance. Key words：clock skew, ADDLL, ATMT.