Low Noise Amplifier – The Work Horse of a Radio Receiver

A low noise amplifier is an electronic device that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio.

An amplifier will increase the power of both the signal and the noise present at its input, but the amplifier will also introduce some additional noise.

Low noise amplifiers or LNAs are designed to minimize such additional noise. The amplifier designers are able to bring this noise reduction by using low-noise components, operating points and circuit topologies.

Minimizing additional noise must be in sync with the other design goals such as power gain and impedance match.

For a low noise, high amplification is required for the amplifier in the first stage. And therefore, they are fitted with junction-field-effect transistors (JFETs) and high-electron-mobility transistors (HEMTs). They are driven in a high-current regime which reduces the relative shot noise. It also requires input/output impedance matching circuit to enhance the gain.

Low Noise Amplifier is

A typical LNA will supply a power gain of 100 (20decibles) while reducing the signal to noise ration by less than a factor of two (3 decibel noise figure).

 To optimize the retrieval of the desired signal in the later stages of the circuitry, low noise amplifier is placed close to the signal source and therefore the noise level is reduced by the signal gain created by the LNA.

Low Noise Amplifier, a key component of any radio receiver, helps to restore or enhance the strength of only the desired signals and cut out on the distortions caused by generated by the other signals and/or the circuitry.