Built-in speed grading with a process-tolerant ADPLL

Speed grading has becoming more and more important for nanometer technologies to support activities like process monitoring or performance diagnosis. In this work, we analyze the feasibility of providing such a capability through on-chip circuitry. This Built-In Speed Grading (BISG) methodology uses an All-Digital Phase-Locked Loop (ADPLL) as the programmable clock generator to provide various clock signals,within a specific frequency range. The maximum operating speed of a circuit can thus be easily tracked down using a binary search process with multiple runs of built-in self-test. To accommodate larger process variation, we further explore a so-called binary-neighborhood-linear frequency-locking scheme for the underlying ADPLL, and thereby resulting in a higher accuracy. Experimental results show that only 2289 gates are adequate to provide this valuable infrastructure that may find numerous applications in IC testing and diagnostics.