Semiconductor device tester for measuring skew between output pins of a semiconductor device

Abstract

Semiconductor device testers are provided which measure skew between two or more output pins of a semiconductor device independent of a strobe timing input. More particularly, a skew signal is generated by a comparator circuit that changes state when the respective outputs transition state, for example, from matching to differing states. In a two output pin embodiment, for instance, when one of the output pin changes state before the other and both initially are in the same state, a flip flop is set at the time when the data on the output pins first differs, i.e. when the first output pin transitions to a new state. The flip flop is then reset when the second output pin subsequently transitions to the new state and again matches the first output pin. The resulting duration of the output of the flip flop thereby corresponds to the time of skew of the output pins regardless of the initial state of the pins.