in an analog test system for testing integrated circuit chips , ac level calibration is achieved by adding a minimal number of new elements and more fully utilizing elements existing in the system . a reference voltage from an existing precision dc power source is fed to an analog switching device . a control signal is also fed into the analog switching device from an existing digital signal generator . based on the control signal , the analog switching device converts the reference voltage into a rectangular waveform signal , which is then digitized . the digital signal is analyzed , and data from the digital signal is compared with reference data , and the ac level error , if any , is determined . ac level calibration is based on this error .