Concise Summary of VLSI Circuits Testing and Verification

Testing and Verification of VLSI Circuits

Key Themes

  • Moore's Law: Predicts growth in complexity (e.g., transistor count doubling approximately every two years).

    • Significant increase from 4004 (1970) to current complex chips.

  • Microprocessor Cost Trends:

    • Testing costs may exceed design/manufacturing costs.
    • Cost per transistor decreasing over years from 1980-2015.
Challenges in VLSI Design

  • As technology advances:

    • Chip sizes decrease while power densities increase.
    • This can lead to excessive heating and leakage power issues.

  • Design Synthesis:

    • Involves processes from specifications to the final test of chips delivered to customers.
Design Flow Process
  • RTL Design ➞ Synthesis ➞ DFT Insertion ➞ IO Insertion ➞ Placement ➞ Routing ➞ Post-silicon Validation.
  • 75% development time spent on verification and debug processes.
Verification vs. Testing
  • Verification: Ensures design conforms to specified functionalities through simulations.
  • Testing: Involves electrical tests to verify functionality post-manufacturing.
    • Test generation and application approaches must be robust, including coverage against defects and faults.
Cost Considerations in Testing
  • Automatic test equipment (ATE) costs vastly contribute to overall manufacturing expenses.
  • Activities include Test Generation, Simulation, and Fault Simulation.
Challenges in Testing
  • Complexity of testing grows with circuit size; exhaustive testing impractical.
  • Imperfections like manufacturing faults require detection without overwhelming duration (e.g., theoretical tests for a 3-input NAND circuit).
Yield and Fault Modeling
  • Yield: Percentage of defect-free chips (Y) - crucial for cost analysis and profitability.
  • Models for analyzing defects include Gross area defects, Random spot defects influencing yield significantly.
Fault Simulation Algorithms
  • Various algorithms exist for testing efficiency:
    • Serial: Each fault simulated one at a time; simple but slow.
    • Parallel: Faster, using parallelism in logic operations.
    • Deductive: Models possible faults based on logical equations and implications in circuits.
Test Pattern Generation (TPG) Methods
  • TPG identifies required input patterns to adequately test circuits.
  • Popular techniques include D-algorithm, PODEM, and FAN algorithms, focusing on fault paths and implications.
Summary of Testing Principles
  • Ensure comprehensive test coverage to minimize defect levels (goal < 100 DPM).
  • Implement multiple strategies to analyze and optimize fault detection (e.g., unique sensitization) efficiently.
Code of Conduct in VLSI Testing
  • Equivalency and dominance rules help in the simplification of fault lists, fostering efficiency in testing methodologies.
  • Understanding fault types (stuck-at, bridging) enhances targeted testing methods for VLSI components.