This paper presents a design-for-testability method for detecting delay faults. In order to observe the effect of small delay defects, we present modified boundary scan cells in which a time-to-digital converter (TDC) is embedded. In our boundary scan cells, flip-flops are utilized for both making a scan path and capturing circuit response. The architecture of the boundary scan design is proposed to detect delay from the other cores or chips or its interconnects. The basic operation of the design is evaluated by simulation and by experimental ICs. Experimental results show that the measurement of the transition delay can be achieved by the boundary scan design with the time-to-digital converter.

SUMMARYThis paper proposes a method for testing delay faults using a boundary scan circuit in which a time-to-digital converter (TDC) is embedded. The incoming transitions from the other cores or chips are captured at the boundary scan circuit. The TDC circuit is modified to set the initial value for a delay line through which the transition is propagated. The condition for measuring timing slacks of two or more paths is also investigated since the overlap of the signals may occur in the delay line of the TDC in our boundary scan circuit. An experimental IC with the TDC and boundary scan is fabricated and is measured to estimate the delay of some paths measured by the TDC embedded in boundary scan cells. The simulation results for a benchmark circuit with the boundary scan circuit are also shown for the case that timing slacks of multiple paths can be observed even if the signals overlap in the TDC.

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