15-10-2012, 03:58 PM
AC AND DC CHARACTERSTIC OF OPAMPLIFIRE
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Operational amplifier
An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output.Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation. High input impedance at the input terminals and low output impedance are important typical characteristics.
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer,
industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production
volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities. Op-amps sometimes come in the form of macroscopic components, or 'cells' or patterns that can be reprinted several times on one chip that is more complex, such as for a cell phone.
Modern designs are electronically more rugged than earlier implementations and some can sustain direct short circuits on their outputs without damage.
Golden rules of op-amp negative feedback
If there is negative feedback and if the output is not saturated,
1. both inputs are at the same voltage;
2. no current flows in or out of either input.
These rules are true of the ideal op-amp and for practical purposes are true of real op-amps unless very high-speed or high-precision performance is being contemplated (in which case account must be taken of things such as input capacitance, input bias currents and voltages, finite speed, and other op-amp imperfections, discussed in a later section.)
As a consequence of the first rule, the input impedance of the two inputs will be nearly infinite. That is, even if the open-loop impedance between the two inputs is low, the closed-loop input impedance will be high because the inputs will be held at nearly the same voltage. This impedance is considered as infinite for an ideal opamp and is about one megohm in practice.
1963: First monolithic IC op-amp
In 1963, the first monolithic IC op-amp, the μA702 designed by at Fairchild Semiconductor, was released. Monolithic consist of a single chip as opposed to a chip and discrete parts or multiple chips bonded and connected on a circuit board a hybrid IC. Almost all modern op-amps are monolithic ICs; however, this first IC did not meet with much success. Issues such as an uneven supply voltage, low gain and a small dynamic range held off the dominance of monolithic op-amps until 1965 when the μA709 was released.