how to choose resonable two-tone freq. for IIp3 simulation?

Right now, I am designing the gsm/scdma dualband LNA, for gsm, channel space is 200k, when I run IIp3 simulation, Rf1=940MHz, so how far away is the RF2? if choose 40MHz away from RF4. do I still get the meaningful IIp3? Also, for scdma, Rf1=1.8GHz, channel sapcing is 500kHz, can I choose RF2=1.795GHz?

Thanks!

Yes, this is the most reasonable thing to do! As both carriers go through the passband, you are interested in what intermodulation falls on the side carriers next to those two!

Thank s for your reply! But do you think it is too far if RF2 is 40MHz away from RF1 ? do I need to consider the channel spacing when I choose Rf2? you know, if I choose small delta f, then PSS will run forever.

I would suggest the two tones equally spaced around the ceter frequency of your real signal and spaced apart about as much as the -1 or -2 dB points on the modulate spectrum of a real signal. This will approximate the modulated signal.

flatulent,

Do you think I will get same IIp3 result if I choose different RF2, like 1MHz or 40MHz away from Rf1?

You probably will. Amplifiers have very complex combinations of nonlinearities that are functions of every possible variable.

The frequency and power level of two tone signals are determined by the

adjacent channel immunity test specification.

In GSM intermodulatation test, the unmodulated carrier power is -49dBm,

and tone spacing is 200kHz.

Of course, in ideal situation, IIP3 is not differed by the tone spacing and

power level of two unmodulated carriers, but in the case of existing

memory effect or sweet spot, the results could be differed.

Best Regards

Channel spacing of GSM is 200KHz. IP3 test frequencies should based on the intermodulation requirement, which is f+800KHz(CW) and f+1600KHz(GMSK). So that 2(f+800KHz)-(f+1600KHz)=f.