Study of different OPAMP circuits like Non-Inverting, Inverting amplifier, Adder & Substractor

Objective:

  • Study of operational amplifier as
  1. Inverting amplifier
  2. Non-inverting amplifier
  3. Differential amplifier
  4. Summing amplifier

Theory:

In this laboratory experiment, you will learn several basic ways in which an op-amp can be connected using –ve feedback to stabilize the gain and increase the frequency response. The extremely high open-loop gain of an op-amp creates an unstable situation because a small noise voltage on the input can be amplified to a point where the amplifier in driven out of its linear region. Also unwanted oscillations can occur. In addition, the open-loop gain parameter of an op-amp can vary greatly from one device to the next. Negative feedback takes a portion of output and applies it back out of phase with the input, creating an effective reduction in gain. This closed-loop gain is usually much less than the open-loop gain and independent of it. 

Closed – loop voltage gain, ACL

The closed-loop voltage gain is the voltage gain of an op-amp with external feedback. The amplifier configuration consists of the op-amp and an external –ve feedback circuit that connects the output to the inverting input. The closed loop voltage gain is determined by the external component values and can be precisely controlled by them. 

Apparatus / Components Required:

  1. Power Supply: Dual variable regulated low voltage DC source
  2. Equipment: Function Generator, DMM (Digital Multimeter)
  3. Resistors:
  4. Semiconductor: IC741 op-amp
  5. Miscellaneous: Bread board and wires 

Inverting amplifier: 

An op-amp connected as an inverting amplifier with a controlled amount of voltage gain is  shown in fig-

The input signal is applied through a series input resistor R1 to the inverting input. Also, the output is fed back through Rf to the same input. The non-inverting input is grounded. An expression for the output voltage of the inverting amplifier is written as

V0=-RfR1×Vin

Procedure: 

  1. Connect the feedback resistance Rf as show in fig.
  2. Connect Non – inverting terminal with ground.
  3. Connect given voltmeter with the output as show in fig, with respective polarity.
  4. Connect Vin with inverting terminal via R1. 

Observation:

Non-inverting amplifier:

An op-amp connected in a closed-loop configuration as a non-inverting amplifier with a controlled amount of voltage gain is shown in Fig

V0 = (1 + Rf/R1)Vin

Procedure: 

  1. Connect the feedback resistance Rf as show in fig.
  2. Connect inverting terminal with ground via R1
  3. Connect given voltmeter with the output as show in fig, with respective polarity.
  4. Connect Vin with Non- inverting terminal. 

Observation: 

Adder:

The Output Voltage, V0 = -Rf (V1/R1+ V2/R2)

If, R1=R2=Rf, then

V0 = – (V1+V2)

 

Procedure:

  1. Connect the feedback resistance RF with the output as shown in fig. note the value of input resistance connected with inverting input of op-amp .as shown in fig. that are resistors are equal in value R1=R2=RF
  2. Connect Non – inverting terminal with ground.
  3. Connect given voltmeter with the output as show in fig, with respective polarity.
  4. Connect V1 and V2 with inverting terminal via R1 and R2.

 Observation: 

Substractor:

If, Rin = Rf = R, then

Vout = V2 – V1

Procedure:

  1. Connect resistances properly with same values.
  2. Connect voltmeter with proper polarity to the output terminal(pin 6).
  3. Connect supply voltages to pin 4 and 7
  4. V1 to the pin2 and V2 to the pin3.

Observation:

Conclusion:

Should follow result in conformation with theory.

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