A Schmitt trigger is an electronic circuit that acts as a comparator with hysteresis, which means it has two threshold voltage levels for switching its output state. It is commonly used to convert an analog signal into a digital signal by "conditioning" or shaping the signal. The primary purpose of a Schmitt trigger is to provide noise immunity and eliminate rapid switching or bouncing of the output due to small fluctuations in the input signal.
Here's how a Schmitt trigger works and how it conditions signals:
Voltage Thresholds: A Schmitt trigger has two voltage threshold levels: a higher voltage level called the upper threshold (Vhigh) and a lower voltage level called the lower threshold (Vlow). These thresholds determine when the Schmitt trigger changes its output state.
Hysteresis: The key feature of a Schmitt trigger is hysteresis, which introduces a "dead zone" between the upper and lower threshold levels. This means that the input voltage must cross a higher threshold to switch the output from a low state to a high state, and it must drop below a lower threshold to switch the output from a high state to a low state. This helps prevent false triggering due to small noise fluctuations around the threshold levels.
Signal Conditioning: When an analog signal is applied to the input of a Schmitt trigger, the circuit compares the input voltage to the upper and lower thresholds. If the input voltage rises above the upper threshold, the output switches to a high state. If the input voltage falls below the lower threshold, the output switches to a low state. However, if the input voltage is within the dead zone between the upper and lower thresholds, the output retains its current state, even if the input voltage fluctuates slightly.
Noise Immunity: Due to the hysteresis, the Schmitt trigger is less sensitive to small noise or voltage fluctuations around the threshold levels. This noise immunity helps prevent unwanted rapid switching of the output due to minor signal variations.
Digital Signal Conversion: By using a Schmitt trigger, you can convert an analog signal into a digital signal with well-defined high and low states. This is useful in various applications where a clean digital signal is required to interface with digital logic circuits or microcontrollers.
Schmitt triggers find applications in many areas, such as debouncing switches, signal conditioning, level shifting, and square wave generation. They are particularly useful in scenarios where input signals may have noise or fluctuations that could lead to unreliable switching if a simple comparator were used.