STA | Advanced Waveform Propagation

• 新工藝新效應；

• 傳統Cell Delay 計算的不足；
  

• 新計算模型；
  

• 新計算模型對library 的要求。

米勒效應：16nm 之后，隨著管子尺寸減小，管子的米勒電容變大，米勒效應不容忽視。米勒效應既可以影響本級Cell Delay 又影響輸出波形形狀。

• Large receivers that are lightly loaded can inject a bump back to the interconnect through the Miller cap (similar to crosstalk);
• Receiver acts as an aggressor driver even though there is no external crosstalk source.

• Waveform is too distorted to be modeled by any pre-driver accurately;
• Distortion is instance specific and cannot be modeled by characterization;
• Representing this complex waveform with delay and slew is not accurate;

為了彌補傳統Cell Delay 計算模型的不足，Innovus 引入了兩種新的計算模型：

• Equivalent WaveForm Model
• Waveform Propagation

• Real waveform tail impact on the next stage is predicted and added to the current wire delay.
• The receiver cell is assumed to be the driver lumped load.

Waveform Propagation: 根據輸入信號的波形計算輸出響應及本級Cell Delay, 并將波形信息依次傳遞，其特點是：

• Real waveforms are stored and used as input for the next stage. The input waveform tail impact is used at the appropriate point.

• Unlike EWM-Only, the waveform propagation computes accurate impact of the tail as it uses distributed parasitics of wires.

如果要做Advanced Waveform Propagation 需要lib 里有waveform 信息，在lib 里定義在normalized_driver_waveform 中，該表格有兩個index.

• index_1: 輸入net 的transition; 
• index_2: 工作電壓的百分比；
• vaule: the time when the voltage reaches the index_2 value.

此外，傳統CCS 的2-piece 跟3-piece 的pin cap 模型都不能足夠精確的模擬米勒效應，在先進工藝結點需要N-piece 的pin cap 模型，如ECSM 的8-piece. 所謂的piece 指電壓值，傳統工藝只抽兩個或三個電壓點的pin 電容，現在抽8個，分別是：

• fall transition: 90% 70% 50% 40% 30% 20% 10% and 0.01% of VDD.
• rise transitions:  10% 30% 50% 60% 70% 80% 90% and 99.99% of VDD.