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Metastability (electronics)
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<p>In <a href="/facts/Electronics/E4JhgISq">electronics</a>, metastability is the ability of a <a href="/facts/Digital_electronics/3kJcKbkw">digital electronic</a> system to persist for an unbounded time in an <a href="/facts/Equilibrium_point/DgbGMPkg">unstable equilibrium</a> or <a href="/facts/Metastability/H72SMWof">metastable</a> state. In <a href="/facts/Digital_logic/RHLulvKI">digital logic</a> circuits, a <a href="/facts/Digital_signal/pKYKbxfK">digital signal</a> is required to be within certain <a href="/facts/Voltage/EN2po6N2">voltage</a> or <a href="/facts/Electric_current/Dc1xdnUX">current</a> limits to represent a '0' or '1' <a href="/facts/Logic_level/aa9GrAPg">logic level</a> for correct circuit operation; if the signal is within a forbidden intermediate range it may cause faulty behavior in logic gates the signal is applied to. In metastable states, the circuit may be unable to settle into a stable '0' or '1' logic level within the time required for proper circuit operation. As a result, the circuit can act in unpredictable ways, and may lead to a system failure, sometimes referred to as a "glitch". Metastability is an instance of the <a href="/facts/Buridan%27s_ass/JlnhWxIX">Buridan's ass</a> paradox. </p><p>Metastable states are inherent features of <a href="/facts/Asynchronous_circuit/n4ah2j7H">asynchronous digital systems</a>, and of systems with more than one independent <a href="/facts/Clock_signal/9UfTzGHx">clock</a> domain. In <a href="/facts/Self-clocking_signal/VRaK2817">self-timed</a> asynchronous systems, arbiters are designed to allow the system to proceed only after the metastability has resolved, so the metastability is a normal condition, not an error condition. In synchronous systems with asynchronous inputs, synchronizers are designed to make the probability of a synchronization failure acceptably small. Metastable states are avoidable in fully synchronous systems when the input <a href="/facts/Setup_time/vA99xjM7">setup and hold time</a> requirements on flip-flops are satisfied. </p>