This article is about electronic amplifiers. A 100 watt stereo audio amplifier used in home component audio class a power amplifier pdf in the 1970s. Amplification is fundamental to modern electronics, and amplifiers are widely used in almost all electronic equipment.
Amplifiers can be categorized in different ways. Today, most amplifiers use transistors, but vacuum tubes continue to be used in some applications. De Forest’s prototype audio amplifier of 1914. 5, providing a total gain of approximately 125 for this three-stage amplifier. 1876, created the need to increase the amplitude of electrical signals to extend the transmission of signals over increasingly long distances. Duplex transmission was essential for telephony and the problem was not satisfactorily solved until 1904, when H. The Shreeve repeater was first tested on a line between Boston and Amesbury, MA, and more refined devices remained in service for some time.
1902, provided an entirely electronic method of amplifying signals. In the first extensive commercial use of the vacuum tube, such repeaters powered the first transcontinental telephone line for commercial service in 1915. 1915 when triodes became widespread. For 50 years virtually all consumer electronic devices used vacuum tubes. Power control circuitry used magnetic amplifiers until the latter half of the twentieth century when power semiconductor devices became more economical, with higher operating speeds. Shreeve repeaters were used as adjustable amplifiers in telephone subscriber sets for the hearing impaired until the transistor provided smaller and higher quality amplifiers in the 1950s.
Today, use of vacuum tubes is limited for some high power applications, such as radio transmitters. Many amplifiers commercially available today are based on integrated circuits. For special purposes, other active elements have been used. The core circuit was a diode whose capacitance was changed by an RF signal created locally. Under certain conditions, this RF signal provided energy that was modulated by the extremely weak satellite signal received at the earth station.
Combinations of these choices lead to four types of ideal amplifiers. For any particular circuit, a small-signal analysis is often used to find the actual impedance. Many real RF amplifiers come close to this ideal. Although, for a given appropriate source and load impedance, RF amplifiers can be characterized as amplifying voltage or current, they fundamentally are amplifying power. Amplifiers are described according to the properties of their inputs, their outputs, and how they relate. All amplifiers have gain, a multiplication factor that relates the magnitude of some property of the output signal to a property of the input signal. Most amplifiers are designed to be linear.
That is, they provide constant gain for any normal input level and output signal. Certain signal processing applications use exponential gain amplifiers. The main effect is to reduce the overall gain of the system. However, the unwanted signals introduced by the amplifier are also fed back. Since they are not part of the original input, they are added to the input in opposite phase, subtracting them from the input. Noise, even crossover distortion, can be practically eliminated. Negative feedback also compensates for changing temperatures, and degrading or nonlinear components in the gain stage, but any change or nonlinearity in the components in the feedback loop will affect the output.
All amplifiers include some form of active device: this is the device that does the actual amplification. A transistor is used as the active element. The gain of the amplifier is determined by the properties of the transistor itself as well as the circuit it is contained within. RF high power generation for semiconductor equipment, to RF and microwave applications such as radio transmitters.