What does IIP3 +5dbm mean ?

[novice_user]

Hi all,
I read couple of post on eda board in relevance to the question i am asking still I havent had clarity on this topic.

IP3- defines the linearity of amplifier
Rule of thumb- IP3= P1dB+10 ------ (1)
Means by knowing IP3 i can know P1dB point ...

As the active ckt approaches non-linear region close to P1dB the 2 carriers will generate distortion products both in and out of band.( Reference listed below)

Question 1

So with this knowledge would it be sound to infer that if I know IP3 point i can know P1db compression point and by knowing that point I have knowledge of point till which a active ckt wont generate distortion product.


Question 2

Relationship between IIP3 AND OIP3

IIP3= OIP3- GAIN

So when I read something like IIP3 is +5dBm. What does it mean ?

I mean significance of it..something like my LNA can max operate/be linear till this point ?


Thanks for answers in advance !!!!

And If you could give a bit detailed explanation it would work wonders for me and others at novice level in understanding




**broken link removed**

 

[nitu]

Hi..

Answer 1
Yes, you can infer IIP3 from P1dB and vice-versa. The relation mentioned in (1) is valid when there is no external interference present and true for linear circuits like amplifier.

P1dB is input power level at which the output power is 1dB less when compared to idle case ( Output power = Gain + Input power in dB).

Answer 2
IIP3 = 5dBm means that LNA maximum operating range is lower than 5dBm and user in case apply signal of 5dBm will get distortion at the amplifier output. At 5dBm input power the distortion/intermodulation product power and signal power will same.

Hope this help..

 

[robismyname]

Hi all,
I read couple of post on eda board in relevance to the question i am asking still I havent had clarity on this topic.

IP3- defines the linearity of amplifier
Rule of thumb- IP3= P1dB+10 ------ (1)
Means by knowing IP3 i can know P1dB point ...

As the active ckt approaches non-linear region close to P1dB the 2 carriers will generate distortion products both in and out of band.( Reference listed below)

Question 1

So with this knowledge would it be sound to infer that if I know IP3 point i can know P1db compression point and by knowing that point I have knowledge of point till which a active ckt wont generate distortion product.

I would say that the IP3 is when the non-linear ckt has a input level that causes third order IMD. I remeber that you never want to operate a ckt at the IP3. P1dB is where you reach the non-linear region of the ckt.

Question 2

Relationship between IIP3 AND OIP3

IIP3= OIP3- GAIN

So when I read something like IIP3 is +5dBm. What does it mean ?

For clarity lets assume that the IIP3 is +5dBm and the Gain of the circuit is +10dB.

Knowign this it means that the input signal level of the ckt should not exceed +5dBm. and the output level of the ckt should not exceed +15dBm. So this provides you a way to know what level signal the next stage of your receiver chain can handle without operating the components in the non linear regions. I have used O/I IP3, and O/I P1dB in link budget analaysis to make sure I have the appropriate levels throughout the rx cascaded chain.

Normally the P1dB parameters of the circuit are used instead of the IP3 level.

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[novice_user]

Thanks @nitu and robis for ur replies...It really helped in understanding the concepts...

I would appreciate if u guys can throw some light on this question .

I read in Single tone scenario reciever's LNA is operated in high gain state.

Question 1 )My question is wouldnt the gain provided to tone and desired signal be same?Could it be becoz of fact that since signal is very weak percentage wise we would be increasing desired signal strength compared to tone?

Question 2) What are the advantages of operating LNA in step-wise gain format ?

Thanks in advance