Comparison between LOC and LOS Transition ATPG.

[swethapr565]

Hi,

can any one tell me the comparison between LOC and LOS Transition ATPG? which is advantageous and which one has got limitations. which one of two gives better coverage and why so?

Thank you,
swetha

 

[ranger01]

Its difficult to explain LOS and LOC without proper waveforms and corresponding circuit. But if you have understood the transition faults, following explanation might make some sense to you.

In the case of LOS the transition is launched at the last shift, and it is captured at-speed in the capture mode. If you are using Muxed scan, scan enable signal,which determines the shift/capture mode, should have the transition within the short period of functional frequency. This is the main constraint while using LOS, scan enable signal should be routed as a high frequency signal.

When it comes to LOC, the transition at the fault sites will be launched in the capture period and the launch vector is derived from combinational logic or PIs,(unlike in LOS, where they are loaded on last shift). Hence here the controllability on the fault sites is less when compared to that of LOS, and hence the ATPG runtime increases and there might be slight reduction in coverage. Also there will be a minimum of two pulses with extra dead cycles in the capture mode, hence the tester time also increases substantially.

Take some small circuit and try to figure out how the transition vectors are applied ,then you will appreciate and understand these concepts better.