Low-noise amplifier

Low-noise amplifier

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, so that 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.

LNA 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 is 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 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.

See also


External links

* [http://www.sengpielaudio.com/calculator-thd.htm Conversion: distortion factor to distortion attenuation and THD]

Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Low Noise Amplifier — auch als erste Stufe in einem LNB Als rauscharmer Verstärker bzw. Low Noise Amplifier (LNA) bezeichnet man eine spezielle Art elektronischer Verstärker, die sich schaltungstechnisch durch besondere Rauscharmut auszeichnen, um extrem schwache… …   Deutsch Wikipedia

  • low-noise amplifier — mažatriukšmis stiprintuvas statusas T sritis radioelektronika atitikmenys: angl. low noise amplifier vok. rauscharmer Verstärker, m rus. малошумящий усилитель, m pranc. amplificateur à faible bruit, m …   Radioelektronikos terminų žodynas

  • Low Noise Block Converter — Als rauscharmer Signalumsetzer (engl. low noise block converter [ləʊ nɔɪz blɒk kənˈvɜːtə], kurz LNB) wird die erste, im Brennpunkt einer Parabolantenne befindliche elektronische Baugruppe einer Satellitenempfangsanlage bezeichnet. Sie setzt die… …   Deutsch Wikipedia

  • Low-noise block converter — A low noise block converter (LNB, for low noise block, or sometimes LNC, for low noise converter) is the (receiving, or downlink) antenna of what is commonly called the parabolic (actually paraboloid) satellite dish commonly used for satellite TV …   Wikipedia

  • Amplifier — For other uses, see Amplifier (disambiguation). Generally, an amplifier or simply amp, is a device for increasing the power of a signal. In popular use, the term usually describes an electronic amplifier, in which the input signal is usually a… …   Wikipedia

  • Noise-figure meter — A noise figure meter is an instrument for measuring the noise figure of an amplifier, mixer, or similar device. An example instrument is the 1983 era Agilent 8970A. Contents 1 Measurement methods 2 Noise source 2.1 Thermal noise …   Wikipedia

  • Noise — This article is about noise as an unwanted phenomenon. For other uses, see Noise (disambiguation). NASA researchers at Glenn Research Center conducting tests on aircraft engine noise in 1967 In common use, the word noise means any unwanted …   Wikipedia

  • Noise figure — (NF) is a measure of degradation of the signal to noise ratio (SNR), caused by components in a radio frequency (RF) signal chain. The noise figure is defined as the ratio of the output noise power of a device to the portion thereof attributable… …   Wikipedia

  • Noise (electronics) — Electronic noise [1] is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects. Thermal noise is… …   Wikipedia

  • Electronic amplifier — A practical amplifier circuit An electronic amplifier is a device for increasing the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude. In… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”