Does a 0dBm max. input power system require>=10dBm IIP3?

Dear all,

I have a question, for a system with >=0dBm maximum input power, usually IP1dB>0dBm is used as the spec., for my understanding, IP1dB>=0dBm can promiss >=0dBm single tone input power; but do we need a IIP3 spec for two tone maximu power input? need IIP3>=10dBm?

For example, in Bluetooth system, the signal is in 1MHz bandwidth, can the signal itself intermodulate with itself? if yes, it seems we need to define both IP1dB and IIP3 for a system with >=0dBm max. input power, but what's the relationship between these 2 spec?

Thanks a lot!

Best Regards
Buckaroo

Dear Buckaroo,

First of all the yes the signal can intermodulate itself when it goes in a non-linear device.For example to an Amplifier..if the signal has frequency ω the output is ω..2ω..3ω..4ω.. the harmonics...

In the datasheets of mixers,amlifiers the IIP3 point is commonly reffered and this is what we must know to have a correct function of our devices.

The IP3 is when our signal combines with an another signal (from somewhere else, for example an antenna has a bandwidth that can take not only only our desired signal but and others and then these signals go to an amplifier and intermodulate ) and problems occured.

Hope i helped

Regards,
George

the ip3 requirement for a system depends on the modulation type. FM, for instance, would not need an IP3 specification because it is a constant envelope single tone at all times. some complex modulation types might need +25 dBm IIP3 for a 0 dBm input signal.

Dear Fovakis,

Thanks for your reply, I agree with u.
Now the problem is, when calculating IIP3 spec for a system with >0dBm max input power, what's the power of the two tone? if we take -6dBm for each tone, we get a IIP3 spec., but for a bluetooth with 0dBm power, the PSD is much lower than -6dBm, for example -15dBm, if we use -15dBm as the two tone power, then we get another IIP3 spec, obviously, the latter IIP3 spec is quite relax comparing to the previous IIP3 spec.
I am confused, which IIP3 is correct.

Thanks.

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Dear biff44,

Thanks for your reply, agree, the IIP3 is related to the SNR requirement. e.g, BPSK and QAM64 require different SNR;
But my the problem is, (if we already know the SNR requirement,) when calculating IIP3 spec for a system with >0dBm max input power, what's the power of the two tone? if we take -6dBm for each tone, we get a IIP3 spec., but for a bluetooth with 0dBm power, the PSD is much lower than -6dBm, for example -15dBm, if we use -15dBm as the two tone power, then we get another IIP3 spec, obviously, the latter IIP3 spec is quite relax comparing to the previous IIP3 spec.
I am confused, which IIP3 is correct.

Thanks

Dear buckaroo,

[QUOTE=
Now the problem is, when calculating IIP3 spec for a system with >0dBm max input power, what's the power of the two tone?[/QUOTE]


The two tone constist of 1)your desired signal and 2)another signal that maybe is not desired from you and your antenna can take in its bandwidth. Usually when we want theoritically to find the IIP3 we say "oh lets guess two tones with same amplitue" and then we make some calculations. You must find the calculations for IP3 it is easy i believe to find it in internet.

This is theoritically the IP3. can i have a block diagram of you system?

The power of the two tones should at least 10dB below P1dB of the amplifier. Sometimes even below than 20dB from the P1dB, to be in a safe region.
So measure the P1dB (compression point) of the amplifier (using one tone signal), and after that set the input power of the two tones, and measure IP3.

https://www.macomtech.com/static/pdf...terization.pdf