In this post I will discuss about the Characteristics of the Ideal Operational Amplifier and the ideal attributes of the Operational Amplifier. The operational amplifier is known for its diversity and major reason that makes it so popular among the design engineer is the unique set of quirks that make the Operational Amplifier suitable for analog applications. For example the ideal Operational Amplifier has infinite input impedance, zero output impedance and infinite gain. Here you will see why these attributes are so important in the analog applications. Although the practical Operational Amplifier does not possess exactly these quirks but a good operational amplifier have very high input impedance, very low Output Impedance and very high gain.
After reading this post you will learn about the Operational Amplifier, ideal characteristics of the operational amplifier, the equations determining the Operational Amplifier. So sit back, keep reading and enjoy learning.
Characteristics of the Ideal Operational Amplifier:
It is important to note here that the practical Operational Amplifier has characteristics that closely match that of the ideal Operational Amplifier that is characteristics of the practical Operational Amplifier are not exactly identical to that of the ideal Operational Amplifier. I am mentioning this point here because the practical characteristics has some effects on the operation of the Operational Amplifier configuration that are different form that that are determined from the Operational Amplifier transfer characteristics and the main reason is the mismatch between the ideal attributes and the practical attributes. For the sake of introduction I am discussing here the ideal attributes of the Operational Amplifier and then I will discuss the affects that result due to the practical attributes. One such important effect is the input offset voltage that is according to the ideal attributes of the Operational Amplifier there should be no input offset voltage but the practical attributes will result the non-zero input offset voltage. Let us now discuss the Operational Amplifier ideal attributes.
The symbol of the Operational Amplifier is shown in the figure below:
As the symbol shows that the Operational Amplifier has two input terminals
- Inverting Input Terminal.
- Non-Inverting Terminal.
The inverting input terminal shifts the input signal by the 180 degrees at the output whereas the Non-inverting input terminal of the Operational Amplifier keeps the phase of the output signal intact. Basically the Operational Amplifier is the differential amplifier that is this amplifier amplifies the difference of the signal applied at the inverting and non-inverting input terminals. This feature of the Operational amplifier is utilized in various types of filters.
The Operational Amplifier utilizes the dual power supply that is the positive power supply an d the negative power supply but the single power supply models are also present in Operational Amplifier Integrated Circuits.
Transfer Equation of the Operational Amplifier:
The Operational Amplifier is the dual input single output amplifier. The relationship between the output and input of the ideal Operational Amplifier is described by the transfer equation. The transfer equation of the ideal Operational Amplifier is shown as follows:
The equation enforces the point that I have made in the previous discussion that is, it can be seen by the equation that the ideal Operational Amplifier amplifies the difference between the signals applied at the two input terminals. Vo is the output of the operational amplifier, Vp and Vn are the input signals applied at the non-inverting and inverting input terminals of the Operational Amplifier respectively and finally A is the gain of the Operational Amplifier.
The gain of the Operational Amplifier is represented by the symbol ‘A’. As described in the previous discussion that the ideal Operational Amplifier has the infinite gain. Now it is important to note here that with the infinite gain the operational Amplifier will amplify the input signal by undetermined amount of volts. But the power supply used for the Operational Amplifier is the +/- 12 volts so the output voltage of the Operational Amplifier will get saturated due to the infinite gain as the output signal can exceed the level of 24 volts which is determined by the power supply. So it can be thought that this Operational Amplifier infinite gain is limiting the performance of eth Operational Amplifier. This discussion is made to made the point that the Operational Amplifier is always used in the feedback configuration which controls the gain according to the requirement.
What is impedance?
Before discussing the Input and Output Impedance of the ideal Operational Amplifier let us first consider what the Impedance is. Impedance can be thought of as the resistance but speaking precisely impedance is a combination of the absolute resistance and the imaginary / complex resistance. That is some components manifest the opposition to the current flow due to its dc resistance and the complex resistance which together is known as the Impedance of the component. The input impedance is the resistance seen by the source applied at the input of the component and the output impedance is the resistance that the component manifest at the output terminal.
Infinite Input Impedance:
Another quirk of the ideal Operational Amplifier is the infinite input impedance. The operational amplifier has infinite input impedance which makes it useful in the signal conditioning applications where it is required to input less current to avoid the attenuation already weak signal, in instrumentation and many more. The infinite input impedance of the Operational Amplifier is very desirable as it result in zero input current. The idea of the infinite input impedance of the Operational Amplifier can be visualized from the following figure:
Zero Output Impedance:
Another important feature of the ideal Operational Amplifier is the zero output impedance which makes it very desirable in the signal amplifier. Because of the zero output impedance of the Operational Amplifier it act as the Ideal Voltage Source so with any amount of current flowing through the Op-AMP the signal strength will not be disturbed. As the zero output impedance will result zero voltage drop at the output terminals of the Operational Amplifier so the signal will not get affected irrespective of the amount of current that flows through the Operational Amplifier. The idea of the Output impedance of the operational amplifier can be visualized from the following diagram.
You must have figured out own your own if the practical operational amplifier lacks these ideal attributed what effects will result in the signal. Bu the way the I will write post on effect of the practical attributes of the Operational Amplifier.
That is all for now I hope this article will be helpful for you. In the next post I will come up with more interesting applications of the Operational Amplifier. Till then stay connected, keep reading and enjoy learning.
Characteristics of the Ideal Operational Amplifier is following Infinite Gain,Infinite Input Impedance,Zero Output Impedance of op amp