Using timing flexibility of automatic test equipment to complement X-tolerant test compression techniques

This paper introduces the concept of utilizing the timing flexibility of automatic test equipment (ATE) when designing X-tolerant test compactors. Redundant information is generated by the compactor and transferred to the ATE at a frequency k times higher than the scan shift frequency. This technique is different than current X-tolerant compactors where the necessary redundant information is generated on additional compactor outputs. If the Compactor design can take into account the ATE capabilities, the knowledge of the redundancy can be efficiently used. The ATE will select the relevant information out of the compacted test response, which then leads to a reduction of the ATE compare data by a factor k. In the best case this method can be applied without extra costs related to the higher frequency. The benefit of this approach is a higher parallel test factor due to the reduced number of output pins. This paper explains the capabilities of the employed ATE which need to be taken into account when designing an X-tolerant compactor using a higher output data rate. The method is also demonstrated on a shift register which works at a multiple of the scan shift frequency.