Built-in Clock Skew System for On-line Debug and Repair

We present a low-cost on-line system for clock skew management in integrated circuits. Our built-in clock skew system (BICSS) uses a centralized approach to identify, quantify and correct skew using a two-step method. The technique assesses the time-off-light between the central debug circuitry and each region, or tap under test to account for the measurement error due to differences in path length common in existing techniques. The system can be used to detect skew above a user-adjustable margin using a variable tolerance phase detector. The result is a solution which provides silicon debug and repair capability of on-chip clock skews with a very small area overhead.