test vector

A **test vector** is a specific set of **input signals and expected output responses** used to verify that a semiconductor device functions correctly during testing. Test vectors form the foundation of digital IC testing — they are the "questions" asked of the chip, with the expected answers used to determine pass or fail. **Key Concepts** - **Structure**: Each vector typically specifies the **logic state** (0, 1, or don't-care) for every input pin of the device at a particular clock cycle, along with the **expected output** values. - **Vector Sets**: A complete test program may contain **millions of vectors** covering functional modes, corner cases, timing checks, and stress conditions. - **Coverage**: The quality of a test is often measured by its **fault coverage** — the percentage of possible manufacturing defects that the vector set can detect. **Types of Test Vectors** - **Functional Vectors**: Exercise the chip's intended operations (instruction execution, data processing, I/O protocols). - **Structural Vectors**: Generated by **ATPG (Automatic Test Pattern Generation)** tools targeting specific fault models like **stuck-at**, **transition**, and **path delay** faults. - **Parametric Vectors**: Focus on measuring analog characteristics like voltage thresholds and timing margins rather than pure logic correctness. **Why It Matters** Generating efficient test vectors is a major engineering effort. The goal is achieving **maximum fault coverage** with the **minimum number of vectors** to keep test time — and therefore test cost — as low as possible.