Schmitt Trigger Circuit and its Types
A Schmitt Trigger circuit is an electronic circuit that uses positive feedback to make hysteresis and give two unique edge voltage levels i.e. ‘Upper Threshold Voltage (VUT)’ and ‘Lower Threshold Voltage (VLT)’ for an information signal. It is divided into two parts:
- Op-amp based Schmitt Trigger
- Transistor based Schmitt Trigger
Op-amp based Schmitt Trigger
It is further classified into two types based on the input signal applied on the inverting or non-inverting terminal of Op-amp:
- Inverting Schmitt Trigger.
- Non-inverting Schmitt Trigger
Inverting Schmitt Trigger
When the input is given at the inverting terminal of op-amp and the positive feedback is applied from output to input, it is known as inverting Schmitt Trigger.
Inverting Schmitt Trigger
To determine the equation for Inverting Schmitt Trigger circuit, we use the Kirchhoff Law:
[Tex]\frac{V-0}{R_{1}} + \frac{V-V_{out}}{R_{2}} = 0 [/Tex]
[Tex]V(\frac{1}{R_{1}}+\frac{1}{R_{2}}) = \frac{V_{out}}{R_{2}} [/Tex]
[Tex]V_{out}= \frac{R1+R2}{R1}*V [/Tex]
V= Vin (according to virtual ground property of op-amp)
[Tex]V_{out}= \frac{R1+R2}{R1}*V_{in} [/Tex]
or,
[Tex]V_{in}= \frac{R1}{R1+R2}*V_{out} [/Tex]
Let’s say that Vout is HIGH at Vin = V1. If Vin is more than V1, then Vout has to become low. Hence, V1 is known as Upper Threshold Voltage and similarly for the Lower Threshold Voltage.
Non-Inverting Schmitt Trigger
When the input is given at the non-inverting terminal of op-amp and the positive feedback is applied from output to input, it is known as non-inverting Schmitt Trigger.
Non-Inverting Schmitt Trigger
To determine the equation for Non-Inverting Schmitt Trigger circuit, we use the Kirchhoff Law:
[Tex]\frac{V-V_{in}}{R_{1}} + \frac{V-V_{out}}{R_{2}} = 0 [/Tex]
V=0 (due to virtual ground property)
[Tex]V_{out}= -V_{in}\frac{R2}{R1} [/Tex]
or,
[Tex]-V_{out}\frac{R1}{R2}= V_{in} [/Tex]
Let’s say that Vout is HIGH at Vin = V1. If Vin is less than V1, then Vout has to become low. Hence, V1 is known as Lower Threshold Voltage and similarly for the Upper Threshold Voltage.
Schmitt Trigger
We use Schmitt Triggers in digital electronics. It is used for rejecting the noise from the input signals by using the hysteresis curve. To provide accurate and more stable results, it uses two threshold voltages i.e., upper threshold voltage (VUT) and lower threshold voltage (VLT). It is mainly used in signal conditioning applications to remove noise from signals which is used in digital circuits, particularly mechanical contact bounce in switches. In this article, we will learn more about Schmitt Trigger, its working, and its applications.
Table of Content
- What is Schmitt Trigger?
- Working
- Transfer Characteristics
- Types
- Uses
- Schmitt Trigger Vs Comparator
- Advantages and Disadvantages
- Applications