Everything about Low-noise Amplifier totally explained
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 an 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's necessary for an 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 isn't 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 don't use resistors, as these will add noise. Biasing is done by large resistors, because energy efficiency isn't needed, and a large resistor prevents leakage of the weak signal out of the signal path or noise into the signal path.
Further Information
Get more info on 'Low-noise Amplifier'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://low-noise_amplifier.totallyexplained.com">Low-noise amplifier Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
