What's the difference between LNA and normal amplifier?

WHAT IS DIFFERENCE BETWEEN LNA AND NORMAL AMPLIFIER?

Re: COMMUNICATion

HI DEAR,

The low noise amplifier (LNA) is a special type of electronic amplifier or amplifier used in communication systems to amplify very weak signals captured by an antenna. It is often located very close to the antenna. If the LNA is located close to the antenna, then losses in the feedline become less critical. This "active antenna" arrangement is frequently used in microwave systems like GPS, because coaxial cable feedline is very lossy at microwave frequencies.

It is a key component, which is placed at the front-end of a radio receiver circuit. Per Friis' formula, the overall noise figure of the receiver front-end is dominated by the first few stages.

Using a LNA, the noise of all the subsequent stages is reduced by the gain of the LNA and the noise of the LNA is injected directly into the received signal. Thus, it is necessary for a LNA to boost the desired signal power while adding as little noise and distortion as possible so that the retrieval of this signal is possible in the later stages in the system.

For low noise the amplifier needs to have a high amplification in its first stage. Therefore JFETs and HEMT are used and distributed amplifiers could be used. They are driven in a high current regime, which is not energy efficient, but reduces the relative amount of shot noise. Input and output matching circuits for narrow band circuits enhance the gain (see gain-bandwidth product) and do not use resistors, as these will add noise. Biasing is done by large resistors, because energy efficiency is not needed, and a large resistor prevents leakage of the weak signal out of the signal path or noise into the signal path.

Re: COMMUNICATion

hey buddy copying answers from other sites becomes too easy... try to anwser on your own...


A low noise amplifier is one which immediately follows the tuning circuit in the receiver... when the signal is recieved its magnitude is very small such that the amplifier circuit noise can disort the received signal significantly... so that in the initial stage a low noise amplifier is used... A low noise amplifier could have JFETs and HEMT and distributed amplifiers could be used.

Re: COMMUNICATion

HI DEAR,

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