Operational Amplifiers (Op Amps) Lecture

Introduction to Op Amps

• Op Amp: Short for operational amplifier.
• Function: High Gain differential amplifiers.
• Operation: Amplifies the difference between input voltages ( V_1 ) and ( V_2 ).
• Characteristics:
  • High input impedance.
  • Low output impedance.

Input Terminals

• Inverting Input (Negative Terminal):
  • Signal applied here will be 180° out of phase.
• Non-inverting Input (Positive Terminal):
  • Signal applied here will be in phase.

741 Operational Amplifier Layout

• Pin Configuration:
  • Pin 2: Inverting input.
  • Pin 3: Non-inverting input.
  • Pin 6: Output pin.
  • Pins 4 & 7: Power supply connections.
  • Pins 1 & 5: Offset null pins.

Output Offset Voltage

• Operational amplifier can generate an output voltage without input.
• Offset Null Pins: Used to set output offset voltage to zero.

Inverting Amplifier Circuit

• Configuration:
  • Signal to inverting input (Pin 2).
  • Output is inverted.
• Feedback Resistor (( R_F )):
  • Reduces voltage gain by feeding back output signal.
• Closed Loop Voltage Gain:
  • Formula: (-\frac{R_F}{R_{in}}).
  • ( R ): Parallel combination of input and feedback resistors._

Open Loop Mode

• Removing feedback resistor results in open loop mode.
• Open Loop Voltage Gain:
  • Can be as high as 200,000.
• Output Voltage Limitation:
  • Limited by supply voltages at Pins 4 & 7.

Power Supply Connection

• Using two 9V batteries:
  • Positive terminal connects to Pin 7, negative to Pin 4.
  • Ground in the middle between batteries.

Non-Inverting Amplifier Circuit

• Configuration:
  • Input signal to non-inverting input.
  • Output in phase with input.
• Closed Loop Voltage Gain:
  • Formula: (1 + \frac{R_F}{R_{in}})._

Slew Rate and Frequency

• Slew Rate: Limit on switching speed of transistors inside op amp.
  • Affects maximum operating frequency.
  • Formula: ( \frac{\text{slew rate}}{2\pi \times \text{peak voltage}} ).
• Frequency Limitation:
  • As frequency increases, gain decreases.

Example Problem

• Given: Voltage of input signal.
• Calculate: Closed loop voltage gain and output voltage.
• Circuit Type: Inverting amplifier.
• Calculation:
  • Feedback resistor: 40 kΩ.
  • Input resistance: 2 kΩ.
  • Closed loop voltage gain: (-20).
  • Output voltage for 10V input: 200 mV (out of phase).