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Parameters Of An Op Amp ( Part- I )

written by: Swagatam • edited by: KennethSleight • updated: 11/30/2009

In this part of the article we will learn regarding few basic functions and parameters of Op Amp ICs.

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    Introduction

    The symbol of an op amp is basically represented in the form of a triangle with two inputs, one output and two supply terminals. They can be considered as the building blocks of electronic circuits and has wide and numerous applications. They can be configured into different mathematical operations like addition, subtraction, multiplication etc. and hence the name op amp.

    Op amps are characterized through their following features:

    • Output voltage is defined by the difference of voltages to the inputs.
    • Input resistance is very high, so current through them cannot flow,
    • The amplification is very high, and is given by the formula: A=output voltage / difference in input volts.
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    How an Op amp functions

    opamp symbol According to the symbol of an Op Amp it has an inverting(-) and an non inverting(+) input. The input voltage Vin is basically the difference in voltages applied to these inputs. Thus the output voltage Vout can be shown as:

    V(out)=A( V1+V2 )

    = A.V(in),

    Where A is the amplification of the Op Amp. To understand more regarding the Functions of Op Amps, lets see what are their different parameters :

    • Input and Output Impedance: It is the resistance offered by the inputs and the output terminals to varying voltages. The quantity is expressed in Ohms.
    • Input Bias Current: Some Op Amps incorporate bipolar transistors at their inputs, which require small bias current for switching known as the input bias current and is derived from the input voltage itself.
    • Open Loop Gain: It is the overall voltage gain or the amplification and is calculated in decibels.
    • Input voltage range: This can be any value from 3 volts up to the supply voltage( maximum ). This is the maximum safe voltage limit that the inputs can hold, beyond which the IC may get permanently damaged. A typical input voltage should be around 9volts with a supply voltage of 12 volts.
    • Output Voltage Range: It is never a good idea to over drive an Op Amp IC, if this happens, the out put voltage will saturate and ultimately be limited by the supply voltages. So just like the maximum input voltage, the out put voltage too should be a couple of volts less than the supply voltage.

    In the next part of the article we will discuss regarding few more important parameters of op amps.

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    Sample contents.