regarding upconversion mixer

The LO power is independent of which output mixing product you use. It is set by the technology of the mixer circuit. In general, diode ring mixers require more LO power than active mixers.

i m simulating gilbert cell mixer in 180nm technology.

Each mixer type requires an "optimum" LO power input to operate.
In upconverters with balanced (two-diode) mixers, the IF input should usually be 7 dB below LO input power to maintain linearity.

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Each mixer type requires an "optimum" LO power input to operate.
In upconverters with balanced (two-diode) mixers, the IF input should usually be 7 dB below LO input power to maintain linearity.

why don't u sweep the LO input power with a low enough IF power? Then u can see when ur LO input power saturated