Method and apparatus for implementing enhanced LBIST diagnostics of intermittent failures

Abstract

A method and apparatus are provided for enhanced Logic Built in Self Test (LBIST) diagnostics of intermittent failures. A respective one of a plurality of first multiplexers is coupled between adjacent sequential channels of a plurality of sequential channels under test. Each of the first multiplexers selectively receives a first data input in a first scan mode with the sequential channels configured in a common scan path and a second data input in a second scan mode with each the sequential channels configured in a separate scan path responsive to a first control signal. A second multiplexer, coupled between a test data output of a last sequential channel and the first data input of a first sequential channel; selectively receives the test data output of the last sequential channel and an external test data input responsive to a recirculated control signal. A first multiple input signature register (MISR) including multiple MISR inputs is coupled to a respective one of the plurality of sequential channels under test. A blocker function is coupled between the first multiple input signature register and the plurality of sequential channels under test. The blocker function is configured for blocking all MISR inputs except for a single MISR input receiving the test data output of the last sequential channel responsive to a recirculated control signal. A second MISR shadow register is coupled to the first multiple input signature register. The examination of at least two successive LBIST cycles is enabled so that intermittently failing test cycles can be easily located. The second MISR shadow register stores MISR data for comparison with MISR data from the first multiple input signature register. A plurality of secondary MISR shadow registers with an associated cycle count register can be used for storing MISR data for comparison with MISR data from the first multiple input signature register with a matching cycle count.

Dependencies are inferred from the claim text.