Extrapolate in bit-by-bit mode
通道模擬有分兩種模式，bit-by-bit和Statistical Bit-by-bit是透過給入指定的Bit sequence來分析通道，所以礙於計算能力通常建議最多跑到2e6 bits，但這也衍生一個問題，通常各高速協會規範的觀測眼圖都是看BER = 1e-12，甚至1e-15，為了觀測(或是說估計)高bits數下的眼圖，也只能用外插(extrapolate) 的方式。 ps. 跑1e6 bits，若不做外插，可以看到的有效BER contour是1e-5。 以下是設定外插的方式 但有一個前提，若RX本身已經有設定RJ且佔整體jitter的比重很高，就不須設定外插，因為ADS本來就會用RJ來估計高bits數下的Gaussian noise。 以下是ADS help的說明 Statistical mode provides accurate ultra-low BER contours without the need for extrapolation, and therefore this option is ignored in statistical mode. In addition, if you are running in bit-by-bit mode, and your systems has RJ in the Rx, and that jitter dominates the shape of the ultra-low BER contours, then you don’t need extrapolation, and should clear this option. The reason is that Rx RJ is added as Gaussian noise by post-processing, without the need for extrapolation and without the 10/n limitation mentioned above. 整理一下使用bit-by-bit extrapolation的時機 1. RX jitter行為可以用dual-dirac 來model 2. RX RJ在low-BER的佔比不高 3. 模擬的bit數不能太少，且想要外插的幅度也不要...
