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What Is a Low Noise Amplifier?

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  • Written By: L.S. Ware
  • Edited By: Melissa Wiley
  • Last Modified Date: 06 August 2014
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Electrical systems are composed of a myriad of components, and variations in voltages and currents can cause what is referred to as noise. Many systems, especially wireless communications, utilize a low noise amplifier or preamplifier to boost the signal and reduce the noise. A low noise amplifier is an integral part of many applications, such as cellular phones and wireless local area networks (WLAN). Receivers and antennae utilize the function of a low noise amplifier to maintain the signal-to-noise (SNR) of a particular application.

Amplifiers and preamplifiers vary in size and strength from one application to another. For example, a low noise amplifier used in a military application such as signal interceptors will consume large amounts of power and will typically be quite large. When utilized in the consumer electronics industry, however, a low noise amplifier that runs on a low voltage and integrates easily is preferred.

A low noise amplifier can be developed to conform to a variety of parameters. The most important of these parameters include the levels of power consumption, the gain, and the noise figure. An amplifier combined with a mixer makes up most radio frequency (RF) receivers. The purpose of the amplifier is to receive and boost the incoming signal and feed it to the mixer, which performs frequency conversion.

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Excessive noise is a problem inherent with all wireless communications and is produced by both the electrical components themselves and the external environment. For a low noise amplifier to be effective at boosting a signal without introducing too much of its own noise, the first stage amplification must be high, as must be the gain. Balancing the noise figure and the power gain allows a low noise amplifier to facilitate the reception and transmission of signals in a low power or high noise environment.

Stability at the frequency desired for a particular design is another of the key parameters consistently considered. Power usage and dissipation are also tested and fine-tuned for performance when building amplifiers. The input and output of the amplifier are designed to match as precisely as possible to avoid mismatches that could impair the functionality of the device. Input loads on low noise amplifiers are typically far from ideal, with variations often caused by factors such as environmental fluctuations and input filters. All of the components of a low noise amplifier must be optimized to provide the best performance possible by balancing the parameters of each variable.

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