hold time
The amount of time spent in a phone queue on hold.
hold time: how long a signal waits after the trigger
In digital electronics and circuit design, hold time is the minimum duration a data signal must remain stable at its current logic level after a clock edge arrives. It works in tandem with setup time, which measures the period before the clock edge. Together, these timing parameters define the window during which a latch, flip-flop, or memory device can reliably capture and store data without corruption.
When a flip-flop samples data on a clock pulse, the data input cannot change the moment the clock edge hits. The internal gates need time to fully switch and lock the new value into storage. If the input changes too soon after the clock edge, the cross-coupled gates may become metastable, oscillating between states rather than settling to a definite 0 or 1. Hold time specifies exactly how long the input must stay frozen to prevent this failure mode.
Where hold time matters in practice
Hold time violations are common in synchronous digital design, especially when routing data across multiple clock domains or when clock skew (uneven propagation delays to different parts of a circuit) is present. A designer must verify that all data paths meet both setup and hold time requirements, often using timing analysis tools. Typical hold times in modern CMOS logic range from tens of picoseconds to a few nanoseconds, depending on the device technology and operating voltage.
The term can also apply to analog systems and electromechanical devices. In relay circuits, hold time refers to how long a contact must remain pressed to ensure the relay latches. In some control applications, hold time describes the duration a solenoid or actuator signal must persist to achieve full engagement. The underlying principle is identical: the device needs a minimum window of stability to complete its state transition.
Hold time is distinct from hold current, which is the minimum current needed to keep a device in its latched state. Both terms are critical in logic design and power electronics, but they address different constraints: one is about timing margins, the other about electrical thresholds.