Modeling Dynamic Parasitic Loading Effects on Scan Network Timing Margins
Dynamic parasitic extraction during ATPG shift prevents false timing violations by accounting for state-dependent capacitance and power rail collapses.
Hold Time Breach
Timing Violation
Logic failures occur when a data signal changes state before the minimum required duration has elapsed following a clock edge. A hold time breach prevents a flip-flop from correctly capturing its input data, often leading to unrecoverable errors in a digital system. This failure is independent of the clock frequency and cannot be fixed by slowing down the system.
Violation Mechanism
Root causes usually involve a clock signal arriving too late at the receiving flip-flop or a data signal arriving too early due to insufficient logic delay. When a hold time breach is detected during static timing analysis, designers must insert buffer stages to slow down the data path. This process requires careful balancing to ensure that the added delay does not cause a setup violation at the next stage.
Automated tools prioritize these fixes because hold failures are often fatal to the operation of the device. Delay cells are specifically chosen to match the temperature and voltage coefficients of the original path.
Acceptance Boundary
Verification of the final layout must show zero instances of these errors across all operating corners. A hold time breach that remains in the design will likely lead to a functional defect in the physical silicon regardless of the temperature or voltage. Final sign-off reports provide a list of all timing paths and their respective margins to confirm the structural integrity of the circuit.