LBIST

LBIST stands for Logic Built-In Self-Test. It is a hardware-assisted testing technique that embeds test logic in digital integrated circuits to verify the circuit's logical function. By performing tests on-chip, LBIST enables automatic manufacturing testing and can support in-field diagnostics without reliance on external test equipment.

An LBIST architecture typically includes a test pattern generator based on a linear-feedback shift register (LFSR), a response compressor such as a signature analyzer (often a MISR), and a test controller that sequences tests and controls scan chains. The circuit under test is arranged into scan paths so the LFSR shifts in test vectors and the MISR compresses the observed outputs into a signature. Deterministic or pseudo-deterministic test sets may be generated offline to improve fault coverage for critical logic blocks.

LBIST is commonly implemented at block or IP level in ASICs and SoCs, with an interface to external test access ports (for example, JTAG) and a built-in controller. During a test, the LFSR is seeded, patterns are shifted in, the device clocks, and responses are captured by the MISR. The final signature is compared against a known-good value to determine pass/fail. The approach can include power-management features to limit switching activity. LBIST is distinct from MBIST, which targets memories; its main advantages include reduced dependence on external testers and rapid on-chip fault detection for logic faults, while drawbacks include area overhead and design complexity.