Designed -in-diagnostics: a new optical method

An in-circuit diagnostic test structure triggered by a light pulse captures logic states on-chip with picosecond timing accuracy, and the results read out via a scan chain thus providing precise logic transition time information from deep inside the chip, greatly aiding failure analysis. The method could also make time measurement of switching events inside an IC when it is mounted in a printed circuit board environment, enabling correlation of these events to board level logic timing, i.e. system validation..