IIP is related to Gm of the transistor.Because if you expand Gm relationship into power series, you'll see some coefficients that are related to Ids .If you check Ids vs Vgs ( for instance for pHEMT ) you will see a curve looking a crest.If you take derivative of this
curve, you see nulling point at one single point on the Vgs axis.This is your operating point for zero ( theorotically) second order distortion.
Thanks, BigBoss, for your reply.
But when i take curve Ic vs. Vbe (for bipolar transistor) and then plot it's second derivative - it never becomes zero between 700mV and 900 mV, which is suitable operating range for LNA.
You can check out Jose Pedro's book "Intermodulation Distortion in Microwave and Wireless Circuits" and his publications. He describes how to predict IMDs using transfer function (Ic vs. Vbe in your case) in great detail.
Differentiating Ic vs. Vbe curve obtained from DC measurement may be inaccurate. You can try measure the coefficients at harmonic frequencies. This paper describes this method.
Maas, S.A.; Crosmun, A.; , "Modeling the gate I/V characteristic of a GaAs MESFET for Volterra-series analysis," Microwave Theory and Techniques, IEEE Transactions on , vol.37, no.7, pp.1134-1136, Jul 1989
doi: 10.1109/22.24559
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