Determine system's required IP3 from interference mask

[Ghost Tweaker]

Hi everyone,

I am designing a wireless receiver and I know the target interference mask. How can I then determine the system's IP3 or P1dB from this? I would be tempted to take inband interf. level from the mask and define the input P1dB as the same value and add something like a 5dB margin. Am I wrong? I don't feel confident with this procedure.

Thanx in advance for your help
Regards

 

[hebu]

The "mask" makes me wonder it's used in transmitter rather than receiver.
Would you describe it in more detail?

 

[Ghost Tweaker]

The mask for a receiver defines the maximum power of the interferers allowed by regulations, in and outband. As you can expect, sensitive bands are protected by low inband masks...

 

[biff44]

I would take the highest power density level allowed in one of those interference bands, turn that into two discreet theorectical tones spaced apart by your IF frequency, and use the simple IP3 calculation to see how big a third order product is generated in my IF frequency band. I would then compare this theoretical jammer tone in the IF to the desired IF signal level. The amount of front-end out-of-band filtering will, obviously, lower one or both of the tone levels and will give less interference in the IF.

 

[GDF]

I guess what makes Ghost Tweaker unconfidnet is the 5dB margin is a typical
value or not? I would say it's expensive to get 5dB overdesign.

 

[Ghost Tweaker]

I'm not confident with the two following points:

1) the margin is quite large probably 3dB would be sufficient.

2) Is there a direct relation between the interference mask and the system's P1dB or IP3? My approach would be to say that:

inband: the system's input P1dB should be higher than the inband mask (another question is if this is sufficient or if I should check that at each stage no interferer is higher than the stage input P1dB?)

outband: the same should be verified outband

finally spurious should also be checked

Thanx for your help I have difficulties to cmake things clear...

 

[noiseless]

IIP3=(3*Pblock+G-Pn)/2

When sweep the input signal power level, considering the output signal power level should equal the maximum power level allowed to the input of the baseband without reaching saturation. Pn is the noise power level, Pblock is the max. interfer power, G is the gain of the system.