Sensors and Amplifiers: Sensor Output Signal Amplification Systems

Sensors and Amplifiers: Sensor Output Signal Amplification Systems

Amir Fathi (Urmia University, Iran), Sarkis Azizian (K. N. Toosi University of Technology, Iran) and Nastaran Sharifan (Tehran University, Iran)
DOI: 10.4018/978-1-5225-0736-9.ch016


Sensors are electrical-mechanical elements which are the interface between environment and electrical systems. The input of sensors is characteristics of the environment for example temperature, pressure and etc. and their output is a small electric voltage or current. Their job is to convert environment characteristics to an electric voltage or current at their outputs. Since the output current or voltage is very small, it must be amplified in order to be suitable for use in electronic systems. In this chapter we completely explain the design procedure and characteristics of sensor amplifiers. The important parameters of sensor amplifiers are input and output resistance, gain, unity gain bandwidth and etc. One of the most important characteristics of amplifiers is the linearity of amplification in a way that it must have uniformity for all amplitude voltages or currents in all frequencies of the bandwidth. For this purpose, first the operational amplifier is completely discussed, then the linearity of feedback operation will be explained.
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The signals which are obtained from the environment by sensors have often small amplitudes and need to be amplified for better analysis and interpretation. This job is done by amplifiers which are transistor based circuits.

One of the important evolutions happened in the middle of 20-th century, was the invention of p-n junction diodes which is followed by the invention of bipolar junction transistors. Before that, the diodes were produced from vacuum-tubes and nobody could imagine a good future for these components. Along with the scientific developments, the semiconducting properties of carbon, silicon and germanium were studied and the result was the invention of p-n junction diode composed of P-type and N-type semiconductors. The developments continued and reached to their turning point which led to the introduction of bipolar transistors. With the technology advancements, the mass production of transistors started and an industrial revolution happened. The computers, cell phones and many other devices came to the market and the use of transistors and their amplifying properties continued to grow more and more. With the fabrication of unipolar transistors which are known as FETs and MOSFETs, the technology extended its development. The base of today’s amplifying circuits is still upon transistors and their compounds such as Op-Amps, Comparators, and etc. The only difference is that everything is now being fabricated in a small area of a silicon wafer which is a part of big industry called integrated circuit design technology.

Today different ICs are available in markets with very chip prices and each of them is doing a desired job. In order to have a sufficient knowledge about the behavior of different ICs and their comprising circuits, at first step, we have to collect useful information about the diodes, transistors and their amplifying properties.

This chapter is written to give useful information about the semiconducting based amplifiers which are largely used in the design of electronic circuits and devices. At first, the semiconductors are introduced. Then, their derivatives such as diode, BJT and MOSFET with their complete analysis are introduced. Then the idea will be expanded for multistage amplifiers which leads to OpAmps. Along with the introduction of each semiconductor based component, some of the applications of the component in conjunction with the sensors will be discussed.

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