A Schmitt trigger oscillator is a type of electronic oscillator circuit that generates a continuous square wave output signal. It utilizes the Schmitt trigger, which is a bistable multivibrator circuit, to create a waveform with well-defined high and low voltage levels, resulting in a clean and stable square wave output.
Here's how a Schmitt trigger oscillator works:
Schmitt Trigger: A Schmitt trigger is a type of comparator circuit that has two distinct threshold voltage levels: a higher threshold (Vhigh) and a lower threshold (Vlow). It has positive feedback, which means that the output of the circuit depends not only on the input but also on its previous state. When the input voltage rises above Vhigh, the output switches to a high voltage level (typically the supply voltage, denoted as Vcc). When the input voltage falls below Vlow, the output switches to a low voltage level (usually ground, denoted as 0V).
Positive Feedback: The key to the Schmitt trigger's operation is positive feedback. As the input voltage crosses one threshold, the output switches, which in turn reinforces the change in the input voltage. This leads to a rapid and decisive transition from one output state to another.
Oscillator Configuration: In a Schmitt trigger oscillator, a feedback loop is created using an RC (resistor-capacitor) network. The resistor and capacitor are connected between the Schmitt trigger's output and input. The RC time constant determines the frequency of oscillation. Initially, assume the Schmitt trigger's output is low. As the capacitor charges through the resistor, the input voltage of the Schmitt trigger rises. Once it crosses the higher threshold (Vhigh), the Schmitt trigger switches its output state to high. This rapid change in output state causes the capacitor to discharge through the resistor, bringing the input voltage below the lower threshold (Vlow). This switches the Schmitt trigger output back to low. The cycle then repeats, resulting in a continuous square wave output.
Frequency Control: The frequency of oscillation in a Schmitt trigger oscillator can be adjusted by changing the values of the resistor and capacitor in the feedback network. A larger RC time constant will result in a slower charging and discharging of the capacitor, leading to a lower frequency output, while a smaller RC time constant will yield a higher frequency.
Applications: Schmitt trigger oscillators are used in various electronic applications, including timing circuits, waveform generation, clock generators, and digital systems. They provide a stable and reliable source of square wave signals with well-defined voltage levels, making them useful in many digital and analog circuits.
In summary, a Schmitt trigger oscillator combines the hysteresis characteristics of the Schmitt trigger with positive feedback to create a self-sustaining oscillation circuit that generates a continuous square wave output signal with controlled frequency.