edgetrigger

Edge trigger, or edge-triggering, refers to a property of circuits and measurement systems in which a response occurs only at the moment of a signal’s transition on a clock or timing line. In digital electronics, edge-triggered devices respond to a clock edge—rising (low to high) or falling (high to low)—rather than to the level of the clock. This makes them less sensitive to noise or glitches that may appear while the clock is in a steady state and helps ensure precise sampling of inputs.

Types of edge triggering include rising-edge and falling-edge triggering. Some devices are dual-edge triggered, reacting on both transitions. Many common sequential elements, such as D, JK, and T flip-flops, are implemented as edge-triggered devices to coordinate timing across digital systems.

Mechanisms and design: Edge-triggered behavior is typically realized with two level-sensitive latches arranged in a master-slave configuration or with other circuit techniques that create a short sampling window aligned to the clock edge. The result is that the stored or transferred data changes only at the edge, not while the clock level remains constant. This reduces the time window during which input changes can affect the output, improving synchronization.

Relation to level-triggered devices: Level-triggered (or level-sensitive) circuits respond as long as a clock level satisfies a condition, which can lead to ambiguity if inputs change during the active level. Edge-triggering mitigates this by providing a discrete event for state changes.

Applications and considerations: Edge-triggered elements are fundamental in timing and state machines, counters, and shift registers. They are also used in measurement instruments (such as oscilloscopes) to initiate data capture when an input signal crosses a threshold on a specific edge. Metastability remains a consideration near clock edges, requiring proper timing margins and synchronization between clock domains.