交換電容式類比電路良率提升之設計方法

Design Methodology for Yield Enhancement of Switched-Capacitor Analog Integrated Circuits

羅珮文(Pei-Wen Luo)

指導教授 ： 魏慶隆 ； 陳竹一

國立中央大學/資訊電機學院/電機工程學系/博士(2011年)

摘要

隨著半導體製程的演進以及元件尺寸愈益縮小，製程變動對電路效能的影響已日趨嚴重。顯而易見，在電路設計上直接影響的就是產品良率降低的問題。為了在設計階段先行觀察元件製程變動的影響，一般設計者會透過蒙地卡羅的統計分析方法，將元件變
動的資訊加入電路模擬中。然而，直接在模擬軟體(如：hspice)中，應用統計的方法描述參數變動做電路分析，是相當的耗費時間，甚至對於大電路而言，這是無法實行的模擬方式。類比電路中除了考量製程變動的影響外，對於實體佈局上的元件匹配問題也相
當重視。最常使用共質心方法來消除元件間不匹配現象。然而，這些規則只能用於佈局時的參考準則，並無一個數學判別式用以判斷實際佈局符合規則的程度，並將其數值化。
鑑於先前技術上不足之處，我們提出了運用元件空間相關性模型的混合電路良率評估器，用以同時模擬元件變動及佈局上匹配問題。可以得知許多混合卅類比電路的效能是直接與電容元件比值息息相關。因此，我們將其技術實際應用在交換電容式的混合類
比電路，並在前段設計流程的系統層級中，分析出電容元件的變動與電路效能的關係，並且評估出高良率的佈局架構。除此之外，我們提出了一啓發式演算法以產生一個高良率的佈局架構。基於我們方法建立在設計流程中的前段層級，除了可以大幅度的降低產
品設計上的成本，更能加速產品上市時間。

關鍵字

類比電路 ； 電容擺置 ； 良率提升

並列摘要

As semiconductor technology continues to shrink, the process variation problems will become inevitable. It is anticipated that the problem of uncontrollable process variation will become more serious. As a result, yield loss caused by process variation is becoming an
important design issue. The key performance of many analog circuits is directly related to accurate capacitor ratios. In general, capacitor mismatches caused by process variation can be classified as two types: random mismatch and systematic mismatch. To analyze process variation in early design stages, process variation information must be input to a circuit simulator, where Monte-Carlo analysis is commonly employed to find out process variation
information and to eliminate the random mismatch in the early stages of design. On the other hand, systematic mismatch is mainly due to asymmetrical layout and processing gradients. The common centroid approach is commonly employed to reduce device mismatches caused
by symmetrical layouts and processing gradients. Among the candidate placements generated by the common centroid approach, however, whichever achieves better matching is generally difficult to be determined without performing the time-consuming yield evaluation process.
This study addresses the impact of capacitor correlation on the yield enhancement of switched-capacitor integrated circuits. The relationships between correlation and mismatch and between correlation and variation of capacitor ratio are also presented. Therefore, both
mismatch and variation of capacitor ratio can be expressed in term of capacitor correlation. Based on a spatial correlation model, this study proposes a design methodology for yield enhancement of analog circuits using switched-capacitor techniques. An efficient and
effective placement generator is developed to derive a placement for a circuit to achieve the highest or near highest correlation coefficient and thus accomplishing a better yield performance. A simple yield analysis is also developed to evaluate the achieved yieldperformance of a derived placement. Results show that the proposed methodology derives a placement which achieves better yield performance than those generated by the common
centroid approach. Furthermore, both process variation and device mismatch are considered in the early design phase to reduce the design costs and speed-up the time to market.

並列關鍵字

Yield Enhancement ； Switched-Capacitor Analog Integrated Circuits ； placement

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