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→Comparison between LNA and PA
=== Gain===
An amplifier’s output/input magnitude ratio is gain. In RF, the gain is generally specified in logarithmic scale (dB).
[[File:GainAmpAmp1.pnggif|frame|center]]
=== SNR (Signal to Noise Ratio) ===
The ratio of signal power to the noise power, often expressed in decibels.
[[File:SNRAmpAmp2.pnggif|frame|center]]
=== NF (Noise Figure) ===
It is measures of degradation of the SNR, caused by components in a RF signal chain.
[[File:NFAmpAmp3.pnggif|frame|center]]
=== Bandwidth ===
Noise figure of a component has been defined above. But one can also define the noise figure of a system consisting of multiple components connected in series. NF of this kind of system is define in a very similar way as above with SNRin is the SNR of input to the system and SNRout is the SNR of the output of the system. <br \>
If we know the individual noise figures, we can calculate the noise figure of the system using this formula,
[[File:NFsystemAmp4.pnggif|frame|center]]where Fn is the noise factor for the n-th device, and Gn is the power gain (linear, not in dB) of the n-th device.
=== Need of LNA ===
[[File:Amplifiers5.png|framethumb|thumb500px|RF front end. Image reproduced from [https://commons.wikimedia.org/wiki/File:Superheterodyne_receiver_block_diagram_2.svg here]]]
The signal received by the antenna has a lot of noise. The signal is very close to noise level and any degradation of SNR of the signal will make the signal level go below the noise floor. This will cause the signal to be lost and we can’t get the data from the signal. As we from the above formula the NF of the system is mainly determined by NF of the first device if the gain is very high. As LNA is has a very low noise figure and a very high gain, so the noise figure of the system is very low. The arrangement of antenna followed by LNA is called as an active antenna. Thus LNA is one of the most important part of the RF front end.
* '''Noise Figure:''' The noise figure should be as low as possible.
* '''Linearity:''' If your signal is a broadband signal, the linearity of the the LNA matters. OIP3 (Third Order Intercept Point) is a measurement of the linearity of an LNA. Linearity means that the Harmonics are not produced. (Further explanation of OIP3 can be found [https://en.wikipedia.org/wiki/Third-order_intercept_point here])
[[File:Linearity.png|frame|center|Basic Characteristics of an LNA. Image reproduced from the datasheet of ADL5523, which can be found [http://www.analog.com/media/en/technical-documentation/data-sheets/ADL5523.pdf here]]]
* '''Matching Circuits:''' The input and the output must be matched to 50ᘯ for optimal performance. Every device has a Input and output impedance. These are the impedances looking from input and output respectively. For maximum transfer of power all the impedances of connecting components or tracks or wires should be same. If there is a mismatch the signals may get reflected and damage the amplifier. For more reading one can read Transmission lines. <br \>
If there is a mismatch between input of a connected device and output of the other device and matching circuit has to be designed for impedance matching. Example is shown in the following figure.
[[File:MatchingAmplifiers6.png|frame|center|Impedance Matching Circuit]]
== Power Amplifier (PA) ==
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''The values in the table are take from datasheets for LNA from Analog Devices (ADL5523) and Power Amplifier RF5110G.''
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