Electronic devices have come a long way since the invention of the transistor in 1947 by Bardeen, Brattain, and Shockley.1 Before the transistor was available, vacuum-tube-driven devices, now rarely seen, were the fundamental tools of signal amplification and rectification. The importance of the transistor to electronics can be exemplified in the history of the popular electronics device, the radio. Within a decade of its invention, radio designs began to switch to using transistors, and by the 1970s, billions of these new radios were manufactured, pushing out the older vacuum tube systems. The original transistors were somewhat less than reliable devices, and their failure rate kept the price of transistor radios rather high, even though only a handful of transistors was used in the radio. While these modern radios were highly inferior to the tube radios of the day, they did have a few advantages, such as being smaller, portable, and able to turn on instantly! These attributes made the transistor radio very popular, even if its audio quality was not so great.
Today, we rarely talk about the number of transistors in an electronic device, and in many commercial electronics, you might not even find a discrete transistor. As manufacturers got better at making transistors, the transistors got smaller, and the techniques of combining transistors to perform complex tasks became commonplace. Current electronics can have hundreds and even millions of transistors all contained in a single component, in what is known as an integrated circuit (IC), or more commonly, a chip.
In fact, the more common, primitive (lowest-level) electronic device is often an operational amplifier. An operational amplifier has many transistors within it and provides high-performance amplification that is linear over its operating range. Said another way, if we input a signal, we will get an output signal that is linearly related to the input signal, just with different amplitude!
In this chapter we will expand on the idea of amplification and use
operational amplifiers, or op-amps, to develop circuits that are critically important to working with sensors and transducers. These are all very important tasks for optical engineers.
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