WORKING The amplifiers differential inputs consist of a V+ input and a V− input,and ideally the op-amp amplifies only the difference in voltage between the two,which is called the differential input voltage. The output voltage of the op-amp isgiven by the equation:where V+ is the voltage at the non-inverting terminal, V− is the voltage at theinverting terminal and AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input).The magnitude of AOL is typically very large—100,000 or more for integratedcircuit op- amps—and therefore even a quite small difference between V+ andV− drives the amplifier output nearly to the supply voltage. Situations in whichthe output voltage is equal or greater than the supply voltage are referred to assaturation of the amplifier.
Specification & FeatureInfinite open-loop gain (when doing theoretical analysis, a limit may be taken as openloop gain AOL goes to infinity).Infinite bandwidth (i.e., the frequency magnitude response is considered to be flateverywhere with zero phase shift).Infinite input impedance (so, in the diagram, , and zero current flows from to . )Zero input current (i.e., there is assumed to be no leakage or bias current into thedevice).Zero input offset voltage (i.e., when the input terminals are shorted so that , theoutput is a virtual ground .
Infinite slew rate (i.e., the rate of change of the output voltage is unbounded) andpower bandwidth (full output voltage and current available at all frequencies).Zero output impedance (i.e. so that output voltage does not vary with outputcurrent).Zero noise.Infinite Common-mode rejection ratio (CMRR).Infinite Power supply rejection ratio for both power supply rails.
Advantages The use of negative feedback makes it easy toadjust the voltage gain. The voltage gain obtained ispredictable
Dis-Advantages The disadvantages are the loss of voltage gain and the needfor a high impedance differential amplifier circuit. With the Op-Amp these disadvantages are no longer valid, and mostamplifier systems are designed using op-amps with a negativefeedback loop to control the gain.
ApplicationsUse in electronics system designPositive feedbackNegative feedbackaudio- and video-frequency pre-amplifiers and buffersdifferential amplifiersdifferentiators and integrators filtersprecision rectifiersprecision peak detectorsvoltage and current regulatorsanalog calculatorsanalog-to-digital convertersdigital-to-analog convertersvoltage clampsoscillators and waveform generators