1. TOPIC : Transition Count Compression UNIT 5 : BIST and BIST Architectures Module 5.4 Compression Techniques

2. Transition Count (TC) Signature Assume the output response of a CUT as R = r 1 r 2 r 3 ….r m In this technique, the signature is the number of 0-1 and 1-0 transitions. ‘ ‘ represents modulo addition and 0 ≤ TC(R) ≤ m-1 This technique consists of a transition detector and a counter.

3. TC Technique block diagram The test diagram is shown below:

4. Contd … The output responses are passed on to the transition detector and then the no. of transitions are counted which is the signature. The signatures obtained for each response are compared with the fault-free signature and the faults are detected. A simple transition detector is shown below:

5. Masking Probability Let R0 be the fault-free response and let the no. of transitions be r. 0 ≤ r ≤ m-1, where m is the no. of bits. If the sequence starts from 0, the number of sequences that can occur with r transitions is Similarly, if the sequence starts from 1, the no. of possibilities are Hence the no. of masking sequences are 2 - 1. Hence the masking probability is