A Schmitt trigger is a type of bistable multivibrator circuit that is used to convert an analog input
signal into a digital output signal. It is named after Otto H. Schmitt, who invented it in 1934. The
primary purpose of a Schmitt trigger is to provide a clean, noise-free digital output signal by
introducing hysteresis into the circuit.
Operation: The operation of a Schmitt trigger is based on the principle of hysteresis, which
means that the circuit has two different threshold voltages: one for the rising input signal (upper
threshold) and another for the falling input signal (lower threshold). This behavior helps to
eliminate noise and prevent unwanted triggering due to small fluctuations in the input signal.
When the input signal voltage exceeds the upper threshold voltage, the output of the Schmitt
trigger switches to a high logic level (typically VCC or a positive voltage). The output remains in
this high state until the input signal voltage falls below the lower threshold voltage. At this point,
the output switches to a low logic level (typically GND or a negative voltage).
The difference between the upper and lower threshold voltages is known as the hysteresis band
or hysteresis voltage. This hysteresis band ensures that the Schmitt trigger does not oscillate or
switch back and forth rapidly due to noise or small variations in the input signal.
The Schmitt trigger can be implemented using various circuit configurations, such as an
operational amplifier (op-amp) with positive feedback or a dedicated integrated circuit (IC)
designed specifically for this purpose.
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4. An emitter follower circuit, also known as a common collector amplifier, is a type of transistor
amplifier where the output is taken from the emitter terminal. Here’s a brief discussion and
explanation of the feedback nature in this circuit:
Emitter Follower Circuit:
● Configuration: The input signal is applied to the base of the transistor, the collector is
connected to the supply voltage VCCV_{CC}VCCthrough a resistor, and the output is
taken from the emitter.
● Voltage Gain: The voltage gain of an emitter follower is slightly less than 1, meaning it
provides no amplification of the voltage but rather a buffer between circuits.
● Impedance Matching: It has a high input impedance and a low output impedance,
making it ideal for impedance matching applications.
Nature of Feedback:
● Type of Feedback: The emitter follower circuit employs negative feedback.
● Mechanism:
○ The increased emitter current flows through the emitter resistor, causing a
voltage drop across it, which in turn raises the emitter voltage.
○ This rise in emitter voltage opposes the increase in base voltage, effectively
providing negative feedback.
● Effect of Feedback:
○ Stability: Negative feedback stabilizes the gain of the circuit and makes it less
sensitive to variations in transistor parameters.
○ Linearity: It improves the linearity of the amplifier by reducing distortion.
○ Bandwidth: It increases the bandwidth of the amplifier.
