linearity of gilbert cell

Hi
can you tell me what parameter are affected on linearity of the gilbert cell?

I need some references and paper about this problem

if you expand the large signal characteristic e.g. Ic=IT*tanh(Vin/Vt) into power series, you'll find the coefficient of linear polynom of this equation.Then you can predict nth order nonlinearity of the Gilbert cell..

yes I agree but I want to know how can I measure this problem? just with IIP3? or other parametere?

Yes IIP3 can be measured easily and also you may measure IIP2 to characterize your circuit..