MixedMode BIST Based on Column Matching

1
Mixed-Mode BIST Basedon Column Matching

• Petr Fier

2
Outline

• Introduction to BIST
• State-of-the-art Methods
• Mixed-Mode BIST
• Column-Matching Method
• Experimental Results
• Conclusions
• Publications on Column-Matching
• Further Work

3
Introduction to BIST

• Built-in Self-Test
• Enables the device to test itself
• Why (to) BIST?
• With increasing integration density, the amount
  of manufacture faults is increasing
• Thus, we have to test the chip
• With increasing complexity of the design, it
  becomes impossible to test the chip externally
• Thus, we HAVE to use BIST

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Introduction to BIST

• The BIST Structure
• Generate test patterns
• Apply the patterns to the circuit
• Evaluate the response

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Introduction to BIST

• Two General Approaches to BIST
• Test-per-scan
• Connect the CUT flip-flops into a scan chain
• Test the circuit serially
• Test-per-clock
• Tests the circuit in parallel

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Naive Methods

• Exhaustive Testing
• Generates all the 2n patterns
• Extremely slow impossible to use
• Pseudo-Random Testing
• Apply several pseudo-random patterns to the CUT
• Complete fault coverage is not achieved
• BOM-based BIST
• Test patterns are stored in ROM
• Big area overhead

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State-of-the-art Methods

• Reseeding
• The pseudo-random test patterns are generated by
  LFSR
• More LFSR seeds are applied
• Weighted Pattern BIST
• Change the probability of occurrence of 1s and
  0s in the PR sequence
• Bit-Fixing, Bit-Flipping, Row-matching
• Modify the PR patterns by additional logic

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Mixed-Mode BIST

• Combination of pseudo-random and deterministic
  BIST

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Column-Matching

• LFSR produces code words
• These have to be transformed into deterministic
  patterns(computed by ATPG)
• gt Output Decoder

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Column-Matching

• Basic Principle
• Try to reorder test patterns, so that most of the
  Decoder outputs will be implemented as wires A
  Match
• This will be accomplished when the particular
  columns of the LFSR and test matrix will be equal
• Direct match even the Switch logic is eliminated

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Column-Matching

• Mixed-Mode BIST
• Simulate first n LFSR patterns
• Determine undetected faults
• Compute a test for them (APTG)
• Make a decoder producing test from LFSR patterns
  gt n

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Column-Matching

• Mixed-Mode BIST
• Two separate test phases
• pseudorandom
• and deterministic

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Column-Matching Example
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Column-Matching Example
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Experimental Results
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Conclusions

• Column-matching-based mixed-mode BIST method has
  been presented
• Pseudo-random LFSR patterns are being transformed
  into deterministic vectors generated by ATPG by
  the Decoder
• We try to match as many of the Decoder outputs as
  possible with its inputs, which yields no logic
  necessary to implement these outputs
• Mixed-mode two disjoint BIST phases introduced

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Publications

• Fier, P. - Hlavicka, J. Column-Matching Based
  BIST Design Method. Proc. 7th IEEE Europian Test
  Workshop (ETW'02), Corfu (Greece), 26.-29.5.2002,
  pp. 15-16
• Fier, P. - Hlavicka, J. - Kubátová, H.
  Column-Matching BIST Exploiting Test Don't-Cares.
  Proc. 8th IEEE Europian Test Workshop (ETW'03),
  Maastricht (The Netherlands), 25.-28.5.2003, pp.
  215-216
• Fier, P. - Kubátová, H. An Efficient Mixed-Mode
  BIST Technique, Proc. 7th IEEE Design and
  Diagnostics of Electronic Circuits and Systems
  Workshop 2004 (DDECS'04), Tatranská Lomnica, SK,
  18.-21.4.2004, pp. 227-230
• Fier, P. - Kubátová, H. Survey of the
  Algorithms in the Column-Matching BIST Method,
  Proc. 10th International On-Line Testing
  Symposium 2004 (IOLTS'04), Madeira, Portugal,
  12.-14.7.2004, pp. 181
• Fier, P. - Kubátová, H. Pseudorandom
  Testability - Study of the Effect of the
  Generator Type, ECI'04, Herlany, SR, 22.-24.9.04
• Fier, P. - Kubátová, H. Influence of the Test
  Lengths on Area Overhead in Mixed-Mode BIST,
  BEC'04, Tallinn (Estonia), 3.-6.10.2004

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Further Work

• Use more sophisticated structures instead of a
  LFSR (cellular automata)
• Adjust the width of a PRPG
• Incorporate the ATPG into the design process
  iterative test computation
• Test-per-scan support
• Partitioning of the CUT
• Combine CM-BIST with other methods