Sunday, 27 December 2015

Linear Integrated Circuits

The trend toward the use of operational amplifiers as general-purpose analog building blocks began when modular, solid-state discrete-component designs became available to replace the older, more expensive vacuum-tube circuits that had been used primarily in analog computers. As cost decreased and performance improved, it became advantageous to replace specialized circuits with these modular operational amplifiers. This trend was greatly accelerated in the mid 1960s as low-cost
monolithic integrated-circuit operational amplifiers became available. While the very early monolithic designs had sadly deficient specifications compared with discrete-component circuits of the era, present circuits approach the performance of the best discrete designs in many areas and surpass it in a few. Performance improvements are announced with amazing regularity, and there seem to be few limitations that cannot be overcome by appropriately improving the circuit designs and processing techniques that are used. No new fundamental breakthrough is necessary to provide performance comparable to that of the best discrete designs. It seems clear that the days of the discrete-component operational amplifier, except for special-purpose units where economics cannot justify an integrated-circuit design, are numbered. In spite of the clear size, reliability, and in some respects performance advantages of the integrated circuit, its ultimate impact is and always will be economic. If a function can be realized with a mass-produced integrated circuit, such a realization will be the cheapest one available. The relative cost advantage of monolithic integrated circuits can be illustrated with the aid of the discrete-component operational amplifier used as a design example in the previous chapter. The overall specifications for the circuit are probably slightly superior to those of presently available general-purpose integrated-circuit amplifiers, since it has better bandwidth, d-c gain, and open-loop output resistance than many integrated designs.
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