A Schmitt trigger circuit is an electronic circuit that serves as a signal conditioning element. Its primary purpose is to convert an input signal with varying voltage levels into a clean, well-defined digital output signal, which is either in a high state (logic '1') or a low state (logic '0').
The Schmitt trigger is designed to address the issue of signal noise and uncertainty that can arise when an input signal hovers around a certain voltage threshold due to fluctuations or noise. In such cases, a simple comparator circuit might generate erratic or unreliable output transitions, leading to undesirable behavior in downstream digital circuits.
The Schmitt trigger circuit overcomes this problem by introducing hysteresis, which is a feature that introduces a voltage difference between the threshold levels at which the output state switches. The circuit has two threshold levels: a higher threshold (V_high) and a lower threshold (V_low). When the input signal crosses the higher threshold, the output switches from low to high. Conversely, when the input signal crosses the lower threshold, the output switches from high to low.
The introduction of hysteresis helps eliminate small signal fluctuations that might otherwise cause multiple rapid transitions at the threshold level. The Schmitt trigger essentially provides a "snap-action" effect, ensuring that the output remains stable once it has switched states until the input voltage crosses the opposite threshold.
In summary, the primary purpose of a Schmitt trigger circuit is to provide reliable and noise-resistant digital signal transitions by introducing hysteresis to the switching process. This makes it particularly useful for conditioning signals from sensors, noisy environments, or any situation where input voltage levels might be close to the switching threshold.