Amplifiers

Audio frequency amplifiers are used to amplify signals in the range of human hearing, approximately 20Hz to 20kHz, although some Hi-Fi audio amplifiers extend this range up to around 100kHz, whilst other audio amplifiers may restrict the high frequency limit to 15kHz or less.

Audio power amplifiers are used to receive the amplified input from a series of voltage amplifiers, and then provide sufficient power to drive loudspeakers.

Intermediate Frequency amplifiers are tuned amplifiers used in radio, TV and radar. Their purpose is to provide the majority of the voltage amplification of a radio, TV or radar signal, before the audio or video information carried by the signal is separated (demodulated) from the radio signal. They operate at a frequency lower than that of the received radio signal, but higher than the audio or video signals eventually produced by the system.

Radio Frequency amplifiers are tuned amplifiers in which the frequency of operation is governed by a tuned circuit. This circuit may or may not, be adjustable depending on the purpose of the amplifier. Bandwidth also depends on use and may be relatively wide, or narrow. Input resistance is generally low, as is gain. (Some RF amplifiers have little or no gain at all but are primarily a buffer between a receiving antenna and later circuitry to prevent any high level unwanted signals from the receiver circuits reaching the antenna, where it could be re-transmitted as interference).

Ultrasonic amplifiers are a type of audio amplifier handling frequencies from around 20kHz up to about 100kHz; they are usually designed for specific purposes such as ultrasonic cleaning, metal fatigue detection, ultrasound scanning, remote control systems etc. Each type will operate over a fairly narrow band of frequencies within the ultrasonic range.

Wideband amplifiers must have a constant gain from DC to several tens of MHz. They are used in measuring equipment such as oscilloscopes etc. where there is a need to accurately measure signals over a wide range of frequencies. Because of their extremely wide bandwidth, gain is low.

DC amplifiers are used to amplify DC (0Hz) voltages or very low frequency signals where the DC level of the signal is important. They are common in many electrical control systems and measuring instruments.

Video amplifiers are a special type of wide band amplifier that also preserve the DC level of the signal and are used specifically for signals that are to be applied to CRTs or other video equipment. The video signal carries all the picture information in TV, video and radar systems. The bandwidth of video amplifiers depends on use. In TV receivers it extends from 0Hz (DC) to 6MHz and is wider still in radar.

Buffer amplifiers are a commonly encountered, specialised amplifier type that can be found within any of the above categories, they are placed between two other circuits to prevent the operation of one circuit affecting the operation of the other. (They ISOLATE the circuits from each other). Often buffer amplifiers have a gain of one, i.e. they do not actually amplify, so that their output is the same amplitude as their input, but buffer amplifiers have a very high input impedance and a low output impedance and can therefore be used as an impedance matching device. This ensures that signals are not attenuated between circuits, as happens when a circuit with a high output impedance feeds a signal directly to another circuit having a low input impedance.

Operational amplifiers (Op−amps) have developed from circuits designed for the early analogue computers where they were used for mathematical operations such as adding and subtracting. Today they are widely used in integrated circuit form where they are available in single or multiple amplifier packages and often incorporated into complex integrated circuits for specific applications.