The presentation discusses the Schmitt Trigger, an electronic circuit that detects voltage levels and quickly changes output when thresholds are crossed. It utilizes positive feedback to enhance input signals, employs a voltage divider for negative feedback, and highlights the importance of hysteresis to mitigate noise. The design process involves calculating resistor values to establish threshold levels that dictate the circuit's switching behavior.

1. WELCOME
TO MY PRESENTATION
Today’s Topic
Schmitt Trigger

2. S.M.SHAFIUL AZAM
Student I’d:221321007
Semester: Third
Batch:29th
Department of EEE
Varendra University
SARAF ANIKA ISLAM
Student I’d:221321006
Semester: Third
Batch:29th
Department of EEE
Varendra University

3. Introduction
A Schmitt trigger is an electronic circuit that is used to detect
whether a voltage has crossed over a given reference level.
A Schmitt trigger circuit is a fast-operating voltage-level
detector.
When the input voltage arrives at the upper or lower trigger
levels, the output changes rapidly.

5. Schmitt trigger
Symbols of Schmitt trigger

6. Positive and Negative Feedback
The input voltage vin is applied to the inverting input
terminal and the feedback voltage goes to the non-inverting
terminal.
This means the circuit uses positive voltage feedback instead
of negative feedback, that is, in this circuit feedback voltage
aids the input voltage rather than opposing it.

7. Voltage Divider Feedback
The voltage divider feedback a negative voltage to the non-
inverting input, which results in a larger negative voltage.
This feedback more nega­
tive voltage until the circuit is driven
into negative saturation.

8. Schmitt Trigger transfer
Low state
High state
0
0
Vo
Vt- Vt+
Vi

9. Calculation of Resistor
 To design a Schmitt trigger, potential divider current I2 is once again
selected to be very much larger than the op-amp input bias current.
Then the resistor R2 is calculated from equation
R2 = UTP/I2
and R1 is determined from
R1 = (VOUT – UTP) / I2

10. Threshold level
 Whenever the input voltage goes over the High Threshold Level, the
output of the comparator is switched HIGH or LOW.
 The output will remain in this state, as long as the input voltage is
above the second threshold level, the Low Threshold Level.
 When the input voltage goes below this level, the output of the
Schmitt Trigger will switch.

11. Threshold level

12. Transistor Schmitt trigger
A transistor implementation of a Schmitt Trigger is rather
important due to the single voltage supply that requires to
operate the basic Schmitt Trigger circuit with two NPN
transistors.

13. Hysteresis
Hysteresis is desirable in a Schmitt trigger because it
prevents noise form causing false triggering.
The difference between the two threshold voltages is
known as hysteresis
Hysteresis
Hold and measure
Hold and measure
VThreshold
Vinput
Voutput

14. The End…
@shafiulazam
Thank You
@anikaislam