Operational Amplifiers – Complete Theory
Page 12 – Schmitt Trigger
The Schmitt Trigger is a comparator circuit with positive feedback. It introduces hysteresis, which improves noise immunity.
Why Schmitt Trigger?
- Removes noise from signals
- Prevents multiple switching
- Provides stable digital output
Positive Feedback
In this circuit, a portion of the output is fed back to the input.
Positive feedback creates two switching thresholds.
Upper Threshold Voltage (UTP)
UTP = (R1 / (R1 + R2)) × Vsat
This is the voltage at which the output switches from negative saturation to positive saturation.Lower Threshold Voltage (LTP)
LTP = − (R1 / (R1 + R2)) × Vsat
This is the voltage at which the output switches from positive saturation to negative saturation.Hysteresis Width
Hysteresis = UTP − LTP
This difference creates a dead band that removes noise.Transfer Characteristic
- When Vin > UTP → Output = +Vsat
- When Vin < LTP → Output = −Vsat
- Between UTP and LTP → Output remains unchanged
Applications
- Wave shaping circuits
- Noise filtering
- Square wave generation
- Switching circuits
GATE Important Points
- Uses positive feedback
- Introduces hysteresis
- Two threshold voltages (UTP & LTP)
- Improves noise immunity
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