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Originally, op-amps were so named because they were used to model the basic mathematical operations ( add, subtract, integrate, differentiate etc) in electronic analog computers. In this sense a true operational amplifier is an ideal circuit element. The real ones we use, made of transistors, tubes etc, are approximations to this ideal. The ideal op-amp has an infinite open-loop gain, infinite bandwidth, infinite input impedances, zero output impedance and zero noise, as well as zero input offset (0.0V out when both inputs are exactly equal) and no thermal drift. Modern integrated circuit MOSFET op-amps approximate closer and closer to these ideals in limited-bandwidth, large-signal applications at room temperature. When the approximation is reasonably close, we go ahead and call the practical device an 'op-amp', forget its limitations and use the thinking and formulae given in this article.
A typical circuit symbol for an op-amp looks like this:
Its terminals are:
The power supply pins (VS+ and VS−) can be labeled many different ways. For FET based op-amps, the positive, common drain supply is labeled VDD and the negative, common source supply is labeled VSS. For BJT based op-amps, the VS+ pin becomes VCC and VS− becomes VEE. They are also sometimes labeled VCC+ and VCC−, or even V+ and V−, in which case the inputs would be labeled differently. The function remains the same. Often these pins are left out of the diagram for clarity, and the power configuration is described or assumed from the circuit.
The input pin polarity is often reversed in diagrams for clarity. In this case, the power supply pins remain in the same position; the more positive power pin is always on the top, and the more negative on the bottom. The entire symbol is not flipped; just the inputs.
Open-loop gain is defined as the amplification from input to output without any feedbackIn cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. Often this is done intentionally, in order to control the dynamic behaviour of th applied. For most practical calculations, the open-loop gain is assumed to be infinite; in reality, however, it is limited by the amount of voltage applied to power the operational amplifier, i.e. Vs+ and Vs- in the above diagram. This allows the gain in the application to be set simply and exactly by using negative feedback. Of course theory and practice differ, since op-amps have limits that the designer must keep in mind and sometimes work around.
The op-amp gain calculated at DC does not apply at higher frequencies. This effect is due to limitations within the op-amp itself, such as its finite bandwidth, and to the AC characteristics of the circuit in which it is placed. The best known stumbling-block in designing with op-amps is the tendency for the device to resonateThis article is about resonance in physics. For other uses, see Resonance (disambiguation). In physics, resonance is an increase in the oscillatory energy absorbed by a system when the frequency of the oscillations matches the system's natural frequency o at high frequencies, where negative feedback changes to positive feedback due to parasitic lowpasses.