Meaning
Timing error in a synchronous digital circuit where a data signal changes its state before the minimum required duration after a clock edge has passed. A hold-time violation occurs when the delay through the combinational logic path is too short, allowing the new data to arrive at the flip-flop input while the previous data is still being sampled. Timing instability leads to unpredictable logic states and system instability.
Logic Failure
The flip-flop enters a metastable state or captures the wrong data bit when this timing requirement is not met. Lowering the clock frequency fails to resolve a hold-time violation because the error is independent of the period. The data must remain stable for the specific window defined by the library cell characteristics.
Additional Path
Additional buffer stages or the lengthening of the signal trace increases the time the data takes to reach the destination. Designers use these techniques to resolve a hold-time violation during the physical implementation phase of the silicon or board. Careful management of the clock tree skew also helps to maintain the necessary margins across the chip.
Environmental Impact
Variations in temperature and supply voltage alter the propagation speed of the signals through the transistors and wires. A hold-time violation might appear only at the fast process corner where signals move most quickly. Verification across all operating conditions is required to ensure the device remains functional throughout its lifecycle.
