EXPERIMENT OP AMP - OPEN LOOP CHARACTERISTICS Help me write CONCLUSION. for this

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EXPERIMENT OP AMP - OPEN LOOP CHARACTERISTICS

Help me write CONCLUSION. for this experiment. Conclusion in paragraph form. This section should present overall conclusion relating to the original purpose of the study. It should discuss any finding related to the objectives of the experiment. List conclusion in order of importance and link them to the information in previous section of the report.. At least 3 paragraphs/ 400 words, the more the better.

LABORATORY EXERCISE 28 OP AMP OPEN LOOP CHARACTERISTICS Description and Purpose: The operational amplifier (Op Amp) is one of the most useful and most encountered of a the semiconductor devices in electronics. It is an amplifier, which means that its output voltage is equal to its input voltage multiplied by a scale factor called the gain. In other words, it follows the equation: Av X vin n this case the input voltage, is the voltage difference between two input leads, v+ and v a instead of just one input lead and ground. This is not a difficult concept to into account We give new name to this input voltage and call it "vd" o recognize that it is the voltage difference between two input leads The other major concept implied in the op Amp is that the voltage gain Av is very large in the range of tens or hundreds of thousands! The ectual gain is more typically 100,0no, or 10" We give it a special name also the open loop gain, or Awo.. The equation for an Op-Amp is actually 105 X vd This concept has great consequences. One is that the gain is so high that it is never used by itself to make an amplifier. s too high! Instead feedback used to reduce this gain to a much lower and more controlled level. The concept of feedback will become clearer as you progress through the textbook and future labs The purpose of this lab exercise is to gain an o appreciation of what it means to have such a high voltage gain, and to see why the Op-Amp cannot be used by itself for linear applications without having the gain modified by feedback. The Op Amp has such a high gain, it cannot be controlled externally. In order to the Op Amp must be allowed to control itself! be us To see the effects of very high open loop gairl To make attempts to control the output of an op-Amp extemally To see how the op Amp can be made to control itself To see the unity gain Op-Amp configuration. To learn how to make the Universal Test Circuit for an op-Amp OP AMP OPEN LOOP CHARACTERISTICS Lab Exercise 28 page 194

Explanation / Answer

The operational amplifier (Op-amp) is the most widely used semiconductor device. It has high input impedance, low output impedance, high open loop gain which makes it most suitable device to be used as an amplifier. It can work as an oscillator or as an amplifier depending on the type of feedback applied; positive feedback for oscillator and negative feedback for amplifier. It has linear relationship with input voltage and output voltage i.e.

;

where is the output voltage;

is the open loop gain generally of the order of 100,000

and is the input voltage applied, and is given by

To understand the properties of the op-amp, a three part exercise is conducted. In the first part, open loop properties are investigated while the next two parts close loop (negative feedback) properties are investigated.

The first part of the exercise maximum and minimum voltage swing is measured. In this, both the inputs of the op-amp are grounded and output voltage is measured. This voltage is very large because it is generated by the noise at the input terminals of the op-amp and can by nullified by the offset voltage applied at the PIN 5 of the IC. Now,   to the IC is grounded and is connected with the variable supply obtained with the help of a potentiometer. With the help of potentiometer from +12V to -12V can be applied. Now, the input voltages are adjusted to get maximum output voltage swing, +11.21V and -11.91V are obtained. Thus, we can see that the output voltage does not exceeds to +12V and -12V which are applied as the PIN4 and PIN7.

The second part of the exercise examines the negative feedback property of the op-amp. The input voltage is set to 0V, 3V and -4V and differential voltage and output voltage are measured. The output voltage obtained are 1.8mV, 3.056V and -4.09V respectively. The differential voltage obtained are 2.1mV, 0.002V and 1mV respectively. By seeing the output and differential voltages, it can be concluded that the op-amp follows the linear relationship of input-output voltages. It is also concluded that the op-amp is trying that both the input terminals to the ground potential i.e. virtual grounding property of the op-amp.

In the third part of the exercise, the op-amp is connected with negative feedback and the second input is grounded. When the output voltage is measured, it is approx. 0V. Thus, it can be concluded that the effect of noise signal at the input terminal is nullified.

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