Exp to study Opamp as inverting and voltage follower (VLab) 2 PDF

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Experiment: Operational Amplifiers: Voltage Follower and Inverting Amplifier Aim: To study basic properties of Operational Amplifiers: Voltage Follower and Inverting Amplifier

Apparatus: Online (using Virtual Lab (http://vlabs.iitkgp.ernet.in/be/ ) Theory: Operational Amplifier commonly known as Op-Amp, is a linear elcectronic device having three terminals, two high impedence input and one output terminal. Op-Amp can perform multiple function when attached to diffrent feedback combinations like resistive, capacitive or both. Generally it is used as voltage amplifier and the output voltage of the Op-Amp is the diffrence between the voltages at its two input terminals.

Op-Amp shows some properties that make it an ideal amplifier, its open loop gain and input impedance is infinite (i.e.,practically very high), Output impedance and offset voltage is zero(i.e.,practically very low) and bandwidth is infinite(i.e.,practically limitted to frequency where its gain become unity). Inverting Op-Amp The open loop gain(Ao) of the Om-Apm is very high which makes it very unstable, so to make it stable with a controlable gain, a feed back is applied through some external resistor(Rf) from its output to inverting input terminal(i.e.,also known as negative feedback) resulting in reduced gain(cloosed loop gain, Av). So the voltage at inverting terminal is now the sum of the actual input and feedback voltages, and to separate both a input resistor(Ri) is introduced in the circuit. The non inverting terminal of the opamp is grounded, and the inverting terminal behaves like a virtual ground as the junction of the input and feedback signal are at the same potential.

Applying KCL at the virtual earth point, −𝐼𝑖𝑛 + 𝐼𝑓 = 0 𝑉2−𝑉𝑖𝑛 𝑅𝑖𝑛

+

𝑉2−𝑉𝑜𝑢𝑡 𝑅𝐹

=0

For virtual GND, V1=V2=0; 𝑉𝑜𝑢𝑡 𝑉𝑖𝑛

𝑅

= −𝑅𝐹

𝑖𝑛

Also, 𝑅

𝐴𝑖𝑛𝑣 = − 𝑅 𝐹

𝑖𝑛

The closed loop gain of inverting amplifier is independent of Op Amps internal open gain. The negative feedback stabilizes the voltage gain. Voltage Follower Voltage follower can be defined as when the output of the op-amp circuit follows the input of the op-amp directly. So both the input and output voltages are the same. This circuit doesn’t supply any amplification. As a result, voltage gain is equivalent to 1. It is also known as unity gain, buffer & isolation amplifier. This circuit has high input impedance so it is used in different circuits. The voltage follower uses the input signal to give efficient isolation of output. The basic diagram is shown below.

Procedure: Inverting Amplifier (http://vlabs.iitkgp.ernet.in/be/exp17/inverting_opamp.html )

1. Connect the components as mentioned below: L1-L3, L4-L7, L4-L5, L6-L9, L8-L12.(For eg. click on 1 and then drag to 3 and so on.) 2. Click on 'Check Connection' button to check the connections. 3. If connected wrong click on 'Delete all connection' button to erase all the connections. 4. Set the Resistance (R1) Value (1 Kohm - 50 Kohm). 5. Set the Feedback Resistance (Rf) Value (2 Kohm - 100 Kohm). 6. Set input voltage (Vin) (-15 to 15 V). 7. Now note the output voltage and click on 'Add to table' button. 8. Increase the input voltage by a factor of 2 9. Click on 'Plot' button to plot the output voltage vs input voltage. 10. Repeat the experiment for another set of resistance value Voltage Follower – Experiment (http://vlabs.iitkgp.ernet.in/be/exp17/inverting_opamp.html ) 1. Set the Resistance (R1) Value (1 Kohm - 50 Kohm). and Set the Feedback Resistance (Rf) Value (2 Kohm - 100 Kohm). [ For voltage follower, they must be same] 2. Set input voltage (Vin) (-15 to 15 V). 3. Now note the output voltage and click on 'Add to table' button 4. Repeat this for different values of input voltage. 5. Take 5 readings. 6. Make a plot for input and output voltage.

Circuit Diagram: Paste the circuit diagram for (take snapshot from vlab) 1. Inverting Amplifier 2. Voltage Follower

Observation Table: 1. Inverting Amplifier (R1= Rf= ) S.No.

Input Voltage

Output Voltage

Current

Output Voltage

Current

2. Voltage Follower (R1= Rf= ) S.No.

Input Voltage

Plot: 1. Inverting Amplifier 2. Voltage Follower

Calculations: For inverting amplifier, verify the readings with the derived formula for inverting amplifier. Make verification of at least 2 readings.

Conclusion:...