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Introduction
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. To suit it for this
usage, the ideal operational amplifier would have infinite
input impedance, zero output impedance, infinite gain and
an open-loop 3 dB point at infinite frequency rolling off at 6
dB per octave. Unfortunately, the unit cost–in quantity-
–would also be infinite.
Intensive development of the operational amplifier, particularly
in integrated form, has yielded circuits which are quite
good engineering approximations of the ideal for finite cost.
Quantity prices for the best contemporary integrated amplifiers
are low compared with transistor prices of five years
ago. The low cost and high quality of these amplifiers allows
the implementation of equipment and systems functions impractical
with discrete components. An example is the low
frequency function generator which may use 15 to 20 operational
amplifiers in generation, wave shaping, triggering and
phase-locking.
The availability of the low-cost integrated amplifier makes it
mandatory that systems and equipments engineers be familiar
with operational amplifier applications. This paper will
present amplifier usages ranging from the simple unity-gain
buffer to relatively complex generator and wave shaping
circuits. The general theory of operational amplifiers is not
within the scope of this paper and many excellent references
are available in the literature.1,2,3,4 The approach will be
shaded toward the practical, amplifier parameters will be
discussed as they affect circuit performance, and application
restrictions will be outlined.
The applications discussed will be arranged in order of increasing
complexity in five categories: simple amplifiers,
operational circuits, transducer amplifiers, wave shapers and
generators, and power supplies. The integrated amplifiers
shown in the figures are for the most part internally compensated
so frequency stabilization components are not shown;
however, other amplifiers may be used to achieve greater
operating speed in many circuits as will be shown in the text.
Amplifier parameter definitions are contained in Appendix I. |
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发表于 2008-3-31 22:13:33
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