simple questions about RF amplifiers (IP3 and p1dB)..

[actra]

ip3 rf

hello
what does it means the following amplifier specification ?
out put P1dB , output IP3 ?

example :
in the datasheet they say
P1dB = +30 dBm , IP3 = +46 dBm ??

the gain of the amp is 14 dB ????


im totally lost .. what i understand is when i input power to amplifier it amplifies it 14 times (Gain) so the output is more 14 db than the iinput but what is p1db and ip3 of the amplifier ????

thank you vmuch

Added after 1 hours 1 minutes:

ive found (by searching the board) a very good explanation to the parameters :
**broken link removed**

now ill try to explain what i understand ...correct me if iam wrong please...

the P1db specifies the linearity of the amplifier ..

- in our example the maximum output power from the amplifier will be +30dbm = 1 watt...
- the maximum input power to this amplifier will be 16dbm (30dbm"output p1db" - 14db"gain")
- if the input power exceed 16dbm ...for example 18 dbm the amplifier wont amplify it by 14 dB...out of linear region...

AM I correct ???

 

[cmosbjt]

rf ip3

I think so

 

[qyinn]

output p1db

- in our example the maximum output power from the amplifier will be +30dbm = 1 watt...
- the maximum input power to this amplifier will be 16dbm (30dbm"output p1db" - 14db"gain")
- if the input power exceed 16dbm ...for example 18 dbm the amplifier wont amplify it by 14 dB...out of linear region...

Hello, actra

The output power of the amplifier can be higher than 30dBm, but the gain won't be 14dB anymore.
The P1dB = 30dBm means that when you have 30dBm at the output, that value is actually 1dB less than what you would have if the amplifier was still linear. If it was linear, you would have 31dBm at the output, for an input power of 31-14 = 17dBm.

So if you put 17dBm at the input, the output power will be 30dBm. And, as you said, if you increase the input power above 17dBm, the amplification will be less than 14dB.


I hope this helps.

 

[actra]

what is p1db

thank you qyinn for correcting me .... now i can saythat i understand it well

but what about theoutput IP3 ?

 

[lakeoffire]

rf amplifier ip3

I think the output IP3 means that when the output is +46dBm, then the 3rd order intermodulation component will be as strong as the fundamental component.

 

[qyinn]

p1db output power

Due to the non-linearity of the amplifier, at the output will also appear harmonics of the input frequency: 2f0, 3f0, etc. But the third harmonic, 3f0, increases 3 times faster than the fundamental when the input power increases, so they will become equal for a certain power level - this is the IP3 (see the attached figure - sorry that it's not very good quality).

However, you can see in the figure that this is a "virtual" point; it cannot be reached due to the output compression. For this amplifier, IF the gain was constant at 14dB, then at 32dBm input power the output power would be 32+14 = 46dBm at f0 and also 46dBm at 3f0 (and the peak output power would be twice that value, 49dBm, when the signals at f0 and 3f0 add in phase).

 

[actra]

rf p1db

perfect ...
that means
dont exceed the 16dbm (30dbm"output p1db" - 14db"gain") input power for the best performance ? right ?

and is the compression in output power is due to the power wasted in harmnoics ? if u check the graph above ull find that the compression in the output power of the fundamental compoenent starts as the start of the powe of the third order ?

 

[Element_115]

amplifier ip3

The thing to remember about OIP3 is that it will never be reached.
Due to the compression of the Amp. IP3 is extrapolated.
Look at Nationals app notes.
www.national.com/an/AN/AN-884.pdf
Especially look at page 5, this should help.
Cheers

 

[rf100]

amplifier p1db

I do not thinkk IP3 is concerned about 3f0 because third harmonic can be easly supressed by simple filter
the IP3 is about the two tone intermodulatation products, the main products is 2f1-f2 and 2f2-f1 theses products are very difficult to filter out and so they have a special concern

 

[iamchrisk]

rf amp ip3

really ?!
i think oip3 is what qyinn talking about
the 2f1-f2 and 2f2-f1 should be intermodulation of the two tones ,IM3 instead
am i right?!

 

[Ruritania]

what is ip3 of amplifier

I agree with rf100, the IP3 does concern about the fundamental and the 2f1-f2 or 2f2-f1. Moreover, as a matter of fact, IP3 is caused by intermodulation.

Rgs.

 

[qyinn]

25 db p1db amplifier

rf100 and Ruritania are right. I made a mistake. Indeed, IP3 is the effect of two-tone intermodulation.

I also found now this interesting application note (about op amps used in RF) with a nice explanation of P1dB and IP3 (and more):
**broken link removed**