Observability calculation of state variable oriented to robust PDFs and LOC or LOS techniques

To detect delay faults structural scan based delay testing is used. Because of the architectural limitations not each test pair ν₁, ν₂ can be applied at scan delay testing. That degrades test coverage. Enhanced scan techniques were developed to remove restrictions on vector pairs. Unfortunately these techniques have rarely been used in practice because of near doubling of the flip-flop area. Partial enhanced scan approach based on selection of flip-flops was suggested to permit using arbitrary test pair ν₁, ν₂ for the chosen flip-flops. This approach is connected with solving the problem of choice of flip-flops for including them into enhanced scan chains. In the previous papers we suggested algorithms of calculation of controllability and observability estimations for state variables when random sequences are applied to inputs of combinational part of sequential circuit. These estimations represent real properties of the circuit connected with robust PDF manifestation but it is not clear how to use them in the frame of Launch-on-Capture (LOC) or Launch-on-Shift (LOS) techniques applying in practice. In this paper we adopted for LOC and LOS techniques the approach connected with calculation of observability estimation for state variable based on robust PDF manifestation. This approach allows grading flip-flops followed including them in enhanced scan chains.