how to give input to test circuit of basic mixer?

hello everyone,
i've been trying to simulate gilbert mixer in cadence 0.18um tech... while creating test circuit, i saw 'balun' is used in ref manuals. But balun is not giving proper differential outputs with some common mode voltage level,instead it is producing two entirely positive and negative signals. Does dis serves our purpose or do i need to use some other component while converts single ended to differential signals...thanq in advance