A Schmitt trigger is a type of electronic circuit that functions as a comparator with hysteresis. It is commonly used in digital electronics and signal conditioning applications. The primary purpose of a Schmitt trigger is to convert an analog input signal into a digital output signal with improved noise immunity and stability.
Here's how a Schmitt trigger works and how it conditions signals:
Comparator with Hysteresis: A basic comparator takes an analog input voltage and compares it to a reference voltage. If the input voltage is higher than the reference voltage, the output goes high (digital '1'), and if it's lower, the output goes low (digital '0'). However, in some situations, the input voltage might be close to the reference voltage, causing the output to switch rapidly between high and low due to noise or small fluctuations in the input signal. This is undesirable behavior.
Hysteresis: A Schmitt trigger addresses this issue by introducing hysteresis, which means that the thresholds for switching from high to low and from low to high are different. Instead of having a single reference voltage, a Schmitt trigger has two threshold voltages: a higher one (V_high) and a lower one (V_low). The difference between these thresholds is known as the hysteresis voltage (V_hyst). The input must cross V_high to make the output go high, and it must cross V_low to make the output go low.
Signal Conditioning: When the input voltage rises above V_high, the output switches to high. However, for the output to switch back to low, the input voltage must fall below V_low, which is lower than V_high. This difference in thresholds introduces a "dead zone" where small fluctuations around the transition region won't cause rapid switching of the output. This behavior is particularly useful for filtering out noise and ensuring that the output doesn't jitter due to minor fluctuations in the input signal.
In summary, a Schmitt trigger conditions signals by providing noise immunity and stability through hysteresis. It's commonly used in applications where input signals are noisy or have small fluctuations, such as in digital communication, debouncing mechanical switches, generating square waves, and more. By introducing hysteresis, the Schmitt trigger helps prevent rapid switching of the output due to noise and ensures that the output transitions are well-defined and predictable.