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Comparison of LFSR and CA for BIST

Comparison of LFSR and CA for BIST

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Comparison of LFSR and CA for BIST

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  1. Comparison of LFSR and CA for BIST Sachin Dhingra ELEC 7250: VLSI Testing Dhingra: ELEC7250

  2. Introduction • Built-In Self Test • Circuit capable of testing itself • Two major components • Test Pattern Generator • Output Response Analyzer • Implementation of BIST • Linear Feedback Shift Register (LFSR) • Shift Register with feedback path linearly related to the nodes using XOR gates • Cellular Automata (CA) • A collection of nodes logically related to their neighbors using XOR gates Dhingra: ELEC7250

  3. Built-In Self Test Test Mode Normal Operation System Inputs System Circuit Input Outputs Under Isolation Test Circuitry Test Output Pattern Response Generator Analyzer • TPG generates pseudo – random test vectors • Input Isolation Circuitry isolates the normal system inputs from the CUT • Output Response Analyzer performs polynomial division for test data compaction (signature analysis) Test Controller Dhingra: ELEC7250

  4. Linear Feedback Shift Register (LFSR) • Two Types • External Feedback • Internal Feedback • Characteristic Polynomial • All zero state is invalid • Max. Sequence Length = 2n – 1 • Primitive and Non-primitive • Reciprocal of primitive polynomial is also primitive • P*(x) = xnP(1/x) • Compact Design • Less than one gate per node • Parallel Pattern generation • Signature Analysis • Signature Analysis Register (SAR) • Multiple Input Signature Register (MISR) P (x) = x0 + x1 + x3 + x4 Dhingra: ELEC7250

  5. Cellular Automata (CA) Rule 150 Rule 90 Rule 90 Rule 90 Null boundary condition • One-Dimensional Linear CA • Linear Hybrid Cellular Automata (LHCA) • Linear Cellular Automata Register (LCAR) • “Rules” define the logical relationship of a node with its neighbors • Rule 90 xi(t+1) = xi-1(t)  xi+1(t) • Rule 150 xi(t+1) = xi-1(t) xi(t)  xi+1(t) • Combination of Rules ≡ Characteristic Polynomial of LFSRs • Boundary Condition • Null Boundary Condition – No Feedback ⇒ Faster • Cyclic Boundary Condition – Feedback ⇒ Slower • Highly Random Vectors Dhingra: ELEC7250

  6. Comparison Dhingra: ELEC7250

  7. Summary and Conclusion • LFSRs are more popular because of their compact and simple design • CAs are more complex to design but provide patterns with higher randomness • CAs perform better in detection of faults such as stuck-open or delay faults, which need two-pattern testing • In applications where area overhead is a big concern, LFSRs prove to be a better choice • CAs provide a good alternative for LFSRs when high fault coverage is needed Dhingra: ELEC7250

  8. References • M.L. Bushnell, V.D. Agrawal, Essentials of Electronics Testing for Digital, Memory & Mixed Signal VLSI Circuits, Kluwer Academic Publishers, Boston MA, 2000 • C. Stroud, A Designer’s Guide to Built-In Self-Test, Kluwer Academic Publishers, Boston MA, 2002 • S. Zhang et. al, “Why cellular automata are better than LFSRs as built-in self-test generators for sequential-type faults”, IEEE International Symposium on Circuits and Systems, Vol. 1, pp 69-72, 1994 • P.D. Hortensius et. al, “Cellular automata-based pseudorandom number generators for built-in self-test,” IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, Vol. 8, pp 842 - 859, 1989 • K. Furuya, E.J. McCluskey, “Two-Pattern test capabilities of autonomous TPG circuits,” Proc. of International Test Conference, pp 704 – 711, 1991. • L.T. Wang, E.J. McCluskey, “Circuits for Pseudoexhaustive Test Pattern Generation,” Proc. IEEE International Conference on Computer-Aided Design of Integrated Circuits and Systems, Vol. 7, pp. 1068 – 1080, 1988 • P.D. Hortensius et. al, “Cellular automata-based signature analysis for built-in self-test,” IEEE Transactions on Computers, Vol. 39, pp. 1273 – 1283, 1990 • K. Furuya et. al, “Evaluations of various TPG circuits for use in two-pattern testing,” Proceedings of the Third Asian Test Symposium, pp. 242 – 247, 1994 • M. Serra, et. al, “The Analysis of One Dimensional Linear Cellular Automata and Their Aliasing Properties,” IEEE Trans. on CAD, pp. 767-778, 1990 Dhingra: ELEC7250