An operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals.
Operational amplifiers are important building blocks for a wide range of electronic circuits. They had their origins in analog computers where they were used in many linear, non-linear and frequency-dependent circuits. Their popularity in circuit design largely stems from the fact that characteristics of the final op-amp circuits with negative feedback (such as their gain) are set by external components with little dependence on temperature changes and manufacturing variations in the op-amp itself. continue..

The first Op-Amps were invented during the time of the Second World War... 
• Dr. C. A. Lovell of Bell Telephone Laboratories introduced the Op-Amp...
• George A. Philbrick independently introduced a single vacuum tube operational amplifier in 1948.
• SO, Op-Amps are NOT new!
• The ever-popular 741 monolithic Op-Amp was designed by Dave Fullagar in 1967.... continue..

The ideal op-amp is characterized by seven properties
  •  Knowledge of these properties is sufficient to design and analyze a large number of useful circuits
 Basic op-amp properties
  • Infinite open-loop voltage gain
  • Infinite input impedance
  • Zero output impedance
  • Zero noise contribution
  • Zero DC output offset
  • Infinite bandwidth
  • Differential inputs that stick together  continue..

Operational amplifiers can have either a closed-loop operation or an open-loop operation. The operation (closed-loop or open-loop) is determined by whether or not feedback is used. Without feedback the operational amplifier has an open-loop operation. This open-loop operation is practical only when the operational amplifier is used as a comparator (a circuit which compares two input signals or compares an input signal to some fixed level of voltage). As an amplifier, the open-loop operation is not practical because the very high gain of the operational amplifier creates poor stability. (Noise and other unwanted signals are amplified so much in open-loop operation that the operational amplifier is usually not used in this way.) Therefore, most operational amplifiers are used with feedback (closed-loop operation). continue..

Amplifiers: From Ideal to Real Amplifier specifications: Gain, Gain-Bandwidth Product, Common-Mode Rejection Ratio, Settling Time, Input Impedance, etc are explained and compared for different categories of amplifier. Gain as a function of frequency is dealt with in particular, ...
Analog integrated circuits voltage comparator, precision voltage follower, noninverting amplifier, high-impedance voltmeter, integrator, 555 audio oscillator, 555 ramp generator, PWM power controller, class B audio amplifier
Applications of opamps The general utility of the operational amplifier is derived from the fact that it is intended for use in a feedback loop whose feedback properties determine the feed-forward characteristics of the amplifier and loop combination, opamp applications, pdf file
Basic operational amplifiers circuits operational amplifiers circuits, pdf file
Designing with opamps Basic Rules Of Opamps, Essential Opamp Information, Configurations, Applying Power, The Ideal Opamp, Basic Opamp Circuits, Non-Inverting Amplifier, Inverting Amplifier, Inverting And Non-Inverting Buffers, Interesting Variations Of Basic Circuits, High Impedance Amplifiers, Simulated Inductor, All-Pass Filter, Phase Shift Oscillator, Schmitt Trigger Oscillator
Handbook of operational amplifiers Computation Control Instrumentation, Notation and Terminology, Input Terminals, Output Terminals, Power Connections, Summary of Notation, Electrical Circuit Models, Circuit Notation, The Ideal Operational Amplifier, Defining the Ideal Operational Amplifier, pdf file continue..

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