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Operational Amplifier

• Definition: An operational amplifier (op-amp) is an electronic device that amplifies the input signal and performs mathematical operations such as addition, subtraction, differentiation, and integration.

• Pin Configuration:

  • Pins Overview: 8 pins are associated with the configuration of an operational amplifier.

    • Inverting Terminal (Pin 2): Input signal here produces an output that's 180 degrees out of phase with the input.

    • Non-inverting Terminal (Pin 3): Input signal applied to this terminal produces an output in phase with the input.

    • Output (Pin 6): Output of the op-amp is taken from this pin.

    • Power Supply (Pins 7 & 4): Vcc (positive supply) and Vee (negative supply).

• Voltage Gain Formula:

  • For Inverting Op-Amp:

    • A_v = -R_f / R_{in} (Where R_f is feedback resistance and R_in is input resistance)

  • For Non-Inverting Op-Amp:

    • A_v = 1 + (R_f / R_1)

Differential Amplifier

• Configuration Overview:

  • In a differential amplifier, two input voltages (V1 & V2) are applied to the inverting and non-inverting terminals.

  • Voltage Gain Formula:

    • A_v = (R_f / R_{in})

• Operation:

  • It amplifies the difference between the two input voltages, allowing for common mode rejection, which is useful in noisy environments.

Impedances in Operational Amplifiers

Input Impedance (Z_in)

• Definition: Input impedance is the resistance seen by the source when connected to the input terminals of the op-amp.

• Ideal Op-Amp:

  • Z_in = ∞ (infinite), ensuring no current flows into the op-amp, making it a perfect voltage amplifier.

• Practical Op-Amp:

  • Z_in is high (1 MΩ to 10 TΩ), minimizing the loading effect on the source signal.

Output Impedance (Z_out)

• Definition: Output impedance is the resistance seen by the load connected to the output of the op-amp.

• Ideal Op-Amp:

  • Z_out = 0, allowing the op-amp to drive any load without voltage drop.

• Practical Op-Amp:

  • Z_out is very low (10-100 Ω), ensuring maximum power delivery to the load.

Summing and Difference Amplifiers

Summing Amplifier

• Operation:

  • Summing amplifiers facilitate the weighted sum of multiple input voltages.

• Formula for Output Voltage (V_out):V_out = -R_f imes (V_1/R_in + V_2/R_in + V_3/R_in)

Difference Amplifier

• Operation:

  • Amplifies the voltage difference (V2 - V1) applied at its inverting and non-inverting terminals.

• Formula for Output Voltage (V_out):V_out = (R_f/R_1) × (V2 - V1)

Zero Crossing Detector (ZCD)

• Definition: Circuit that detects when an input signal crosses zero volts using a comparator.

• Operation:

  • Output switches between high and low states when the input goes above or below zero volts. Useful in applications such as waveform shaping and signal synchronization.

Schmitt Trigger Circuits

Non-Inverting Schmitt Trigger

• Function: Converts noisy analog signals into clean digital signals with hysteresis to stabilize output.

• Operation:

  • Positive feedback ensures that the output switches between two stable states based on the input voltage crossing the predefined thresholds.

Inverting Schmitt Trigger

• Function: Similar to non-inverting but inverses the output signal.

• Operation:

  • Provides noise immunity and ensures stable switching for signal processing.

Comparator Circuits

• Function: Compares two input voltages and outputs a high or low signal based on which input is greater.

• Operation:

  • Sharp transitions between high and low outputs, utilized in ZCD and level shifting applications.

Differentiator and Integrator Circuits

Differentiator Circuit

• Operation: Produces an output proportional to the rate of change of the input signal (derivative).

  • Formula: V_out = -RC * (dVin/dt)

Integrator Circuit

• Operation: Produces an output proportional to the cumulative sum (integral) of the input signal over time.

  • Formula: V_out = 1/(RC) ∫Vin dt

Oscillators

Astable Multivibrator

• Function: Generates square waves continuously.

• Operation: Utilizes two transistors to switch states alternately, resulting in periodic output.

Colpitts Oscillator

• Definition: Uses active devices and an LC circuit for frequency generation.

• Operation: Outputs sine waves due to feedback provided by inductors and capacitors.

Silicon Controlled Rectifier (SCR)

• Structure: A four-layer semiconductor device with three junctions that controls the flow of current.

• Operation: IT turns on when a small gate current is applied, and stays on until the current drops below the holding current.

Zener Diode

• Function: Regulates voltage in reverse bias while acting like a normal diode in forward bias.

• Operation: Conducts when reverse voltage exceeds Zener voltage, maintaining a steady output voltage.

Filters

Filter Types

• Low-Pass Filter: Allows low frequencies to pass through; blocks high frequencies.

• High-Pass Filter: Allows high frequencies to pass through; blocks low frequencies.

• Band-Pass Filter: Permits a specific frequency range while blocking others.

• Band-Stop Filter: Blocks a specific frequency range while allowing others to pass.

Capacitor Filters

• Operation: Used to smooth voltage fluctuations by charging and discharging in response to changes in input voltage.