Page 18 - Op Amps Design, Applications, and Troubleshooting

CHAPTER ONE

Basic Concepts of the

integrated Operational

Amplifier

1.1 OVERVIEW OF OPERATIONAL AMPLIFIERS

1.1.1 Brief History
Operational amplifiers began in the days of vacuum tubes and analog computers.
They consisted of relatively complex differential amplifiers witih feedback. The
circuit was constructed such that the characteristics of the overall amplifier were
largely determined by the type and amount of feedback. Thus the complex differ-
ential amplifier itself had become a building block that could function in different
"operations" by altering the feedback. Some of the operations that were used
included adding, multiplying, and logarithmic operations.
The operational amplifier continued to evolve through the transistor era and
continued to decrease in size and increase in performance. The evolution contin-
ued through molded or modular devices and finally in the mid 1960s a complete
operational amplifier was integrated into a single integrated circuit (1C) package.
Since that time, the performance has continued to improve dramatically and the
price has generally decreased as the benefits of high-volume production have
been realized. The performance increases include such items as higher operating
voltages, lower current requirements, higher current capabilities, more tolerance
to abuse, lower noise, greater stability, greater power output, higher input imped-
ances, and higher frequencies of operation.
In spite of all the improvements, however, the high-performance, integrated
operational amplifier of today is still based on the fundamental differential ampli-
fier. Although the individual components in the amplifier are not accessible to
you, it will enhance your understanding of the op amp if you have some appreci-
ation for the internal circuitry.
1.1.2 Review of Differential Voltage Amplifiers

You will recall from your basic electronics studies that a differential amplifier has
two inputs and either one or two outputs. The amplifier circuit is not directly

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