1. The noise contribution of each device in the signal path must be low enough that it will not significantly degrade the Signal to Noise Ratio. According to Friis noise figure equation, the biggest contributor to the noise figure of a receiver is the first component in the chain, which usually is the LNA .
https://en.wikipedia.org/wiki/Friis_formulas_for_noise
『the biggest contributor to the noise figure of a receiver is the first component in the chain, which usually is the LNA .』
Sorry~!! The former is right, the later is wrong.
If so, it means you will have two biggest contributors if you add an external LNA (eLNA). By doing this, with eLNA, the sensitivity should degrade instead of improving.
But, in every cellphone(including the cellphone you are using now, and the latest iPHONE 6S and 6 plus S), the GPS must have one eLNA. Why do we degrade its sensitivity further by adding an eLNA ?????
Besides, if the LNA is the biggest contributor to the noise figure,
it should be called “HNA”—High Noise Amplifier, instead of LNA.
In fact, eLNA does improve sensitivity, that is why the GPS in every cellphone must have one eLNA.
**broken link removed**
it describes
It seems that you want to answer questions in your attached PDF ... and created confusion because your post with all the questions looks like student's homework questions.
The LNA (due to is gain) improve the receiver sensitivity, but due to its inevitable noise figure will also decrease a bit the receiver noise figure. Just add some numbers in the Friis equation and you will understand.
So an LNA, MUST have gain AND very low noise figure, both in the same time, otherwise instead of improving the receiver noise figure it will degrade it.
All right, so you know things. iPHONE 6s and Plus use LNA's. I am little bit confused. What about iPHONE 4, or Samsung 4 mini, or the old Nokia 6121, do they use LNA's?
A SAW filter is not designed to improve linearity. Often it does as its typical in-band insertion loss is 18 dB or so. SAW filters are small , compact and have good filtering features. But an additional IF gain is needed due to the above.
But, the situation only occurs when LNA is the first stage.
The question and answers are not correct generally. The comunication SYSTEM must be considered complete. Improving receiver alone by inserting a LNA can result in system degradation, due to a higher non-linearity and a higher interference level, intermodulation, etc.
If the Low Noise Amplifier (LNA) is not the first stage its name is simple: AMPLIFIER.
Still I don't understand why criterion456 is answering to the questions of Da CHi Wang, if they are the same author.
A SAW filter is not designed to improve linearity. Often it does as its typical in-band insertion loss is 18 dB or so. SAW filters are small , compact and have good filtering features. But an additional IF gain is needed due to the above.
These are RF architecture basics and we would expect designers to be aware of these dependencies. But anyway, still useful for non-RF guys to see the math applied to "real" systems.
- - - Updated - - -
... but wait. I don't agree on the first part of post #14 part where your SAW increases the IIP3. I think your math/data is flawed there, because the SAW will pass an entire band.
Please see the article
Use Selectivity to Improve Receiver Intercept Point
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?