in electronics, a schmitt trigger is a comparator circuit with hysteresis, implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. it is an active circuit which converts an analog input signal to a digital output signal. the circuit is named a "trigger" because the output retains its value until the input changes sufficiently to trigger a change. in the non-inverting configuration, when the input is higher than a certain chosen threshold, the output is high. when the input is below a different (lower) chosen threshold, the output is low, and when the input is between the two levels, the output retains its value. this dual threshold action is called hysteresis and implies that the schmitt trigger possesses memory and can act as a bistable circuit (latch or flip-flop). there is a close relation between the two kinds of circuits: a schmitt trigger can be converted into a latch and a latch can be converted into a schmitt trigger. schmitt trigger devices are typically used in signal conditioning applications to remove noise from signals used in digital circuits, particularly mechanical switch bounce. they are also used in closed loop negative feedback configurations to implement relaxation oscillators, used in function generators and switching power supplies. thumb|250px|the output of a schmitt trigger (b) and a comparator (a), when a noisy signal (u) is applied. the green dotted lines are the circuit's switching thresholds. the schmitt trigger tends to remove noise from the signal. == invention == the schmitt trigger was invented by us scientist otto h. schmitt in 1934 while he was still a graduate student,otto h. schmitt, , journal of scientific instruments 15 (january 1938): 24â26. later described in his doctoral dissertation (1937) as a "thermionic trigger."august 2004 issue of the pavek museum of broadcasting newsletter - http://www.otto-schmitt.org/otto_images/pavekohsbio.pdf it was a direct result of schmitt's study of the neural impulse propagation in squid nerves. ==implementation== === fundamental idea ===  circuits with hysteresis are based on the fundamental positive feedback idea: any active circuit can be made to behave as a schmitt trigger by 
Digital_electronics Electronic_circuits