Alignment correction technique

摘要

An E-beam alignment correction system employing an up-up integration technique. Input signals during each scan period are integrated and digitized then held in respective registers. The value in one register is converted to its negative value then digitally combined with the other value to generate an alignment correction value. This technique eliminates the requirement of positive and negative integrations needed with up-down integration techniques and droop of the sample and hold device as a function of time. A common analog path is used so that errors add out during digital combination of signal values.