Rise time of lossy transmission lines

摘要

Suppose you cascade two lowpass filters having rise times t{sub}a and t{sub}b. You can estimate the rise time of the combination (t{sub}(a+b)) according to the root-sum-of-squares (RSS) formula: t{sub}(a+b)= {the square root of}((t{sub}a){sup}2+(t{sub}b){sup}2). The RSS formula derives from the central-limit theorem, which applies well to the sort of lowpass-filtering effects found in I/O drivers; chip packages; scope probes; BNCs; and other simple, one-pole linear filters.