Basic Opamp Characteristics
Introduction:
An operational amplifier(often opamp) is a DCcoupled highgain electronic voltage amplifier with a differential input and, usually, a singleended output. In this configuration, an opamp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals. It has high input impedance and low output impedance and has the capability to amplify the dc or ac signal. An opamp can be originally designed to perform mathematical operations like summation, subtraction, multiplication, differentiation, integration etc. Nowadays , it can be used for sign changing, rectification, an oscillator circuit, scale changing , voltage regulation , active filters,rectification, wave generators etc.
Operation:
The amplifier's differential inputs consist of a noninverting input (+) with voltageV_{+}and an inverting input (–) with voltageV_{−}; ideally the opamp amplifies only the difference in voltage between the two, which is called the differential input voltage. The output voltage of the opampV_{out}is given by the equation:
whereA_{OL}is the openloop gain of the amplifier (the term "openloop" refers to the absence of a feedback loop from the output to the input).
Fig:circuit symbol of opamp
Opamp characteristics:
An ideal opamp is usually considered to have the following properties:
 Infinite openloop gain G =v_{out}/v_{in}
 Infinite input impedance R_{in}, and so zero input current
 Zero input offset voltage
 Infinite output voltage range
 Infinite bandwidth with zero phase shift and infinite slew rate
 Zero output impedance R_{out}
 Zero noise
 Infinite commonmode rejection ratio(CMRR)
 Infinite power supply rejection ratio.
References
1.R.F. Coughlin, F.F. Driscoll(1982)Operational Amplifiers and Linear Integrated Circuits (2nd Ed)
2.http://www.electrical4u.com/opampworkingprincipleofopamp/
3.http://www.electronicstutorials.ws/opamp/
 The Operational Amplifier, or Opamp as it is most commonly called, can be an ideal amplifier with infinite Gain and Bandwidth when used in the Openloop mode with typical DC gains of well over 100,000 or 100dB.
 An operational amplifier also has zero output impedance, ( Z = 0 ).
 Opamps sense the difference between the voltage signals applied to their two input terminals and then multiply it by some predetermined Gain, ( A ).This Gain, ( A ) is often referred to as the amplifiers “Openloop Gain”.

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