Detecting Fabrication Faults in C-elements

C-elements are used widely in asynchronous VLSI circuits. Fabrication faults in some C-elements can be undetectable by logic testing. Testable designs of static CMOS Celements are given in this paper which provide for the detection of single line stuck-at and stuck-open faults. We show that driving the feedback transistors in the proposed testable static C-element transforms its sequential function into a combinational AND or OR function depending on the driving logic value. This simplifies the testing of asynchronous circuits which incorporate a large number of state holding elements. The scan testable Celement described can be used in scan testing of the asynchronous circuit making the states of its memory elements controllable and observable.