Electronics Technology Handbook

Chapter 4: Basic Amplifier and Oscillator Circuits


Amplifiers and oscillators are important circuits that appear in many different configurations and perform many different functions in modern electronics. Most amplifier and oscillator circuits were originally designed during the vacuum-tube era, and they have been converted to transistors and ICs with modifications that relate primarily to the differences in characteristics of receiving tubes and transistors. This section on amplifiers and oscillators is confined to transistorized and integrated circuits. Amplifier and oscillator tubes that amplify and oscillate in the higher frequency UHF and microwave regions are discussed in Sec. 7, "Microwave and UHF Technology."

Amplifier Circuits

An amplifier is any circuit or device capable of increasing the magnitude or power level of a time-variable signal without distorting its wave shape. Most low-power and low-frequency amplifiers today are electronic circuits that depend on transistors or ICs for their operation. However, there are also vacuum-tube, magnetic, electromechanical, and hydraulic amplifiers. Electronic amplifier circuits are classified by:

  • Application

  • Circuit configuration

  • Coupling (if more than one stage is used)

  • Bandwidth and frequency of the signals being amplified

  • Operating mode or bias

Amplification can be performed by many different kinds of discrete transistorized and integrated circuits. The active devices in these circuits include bipolar junction transistors (BJTs), junction field-effect transistors (JFETs), and metal-oxide semiconductor field-effect transistors (MOSFETs).

Amplifiers can be designed for either voltage or power amplification. Voltage amplifiers increase the voltage level of an applied signal because of the characteristics of the transistor. The output voltage of an amplifier is determined...


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