How do you design an RF mixer and what determines its linearity and noise performance?

RF mixers perform frequency translation by multiplying RF and LO signals. Passive mixers (diode ring, passive FET) have conversion loss but excellent linearity (IP3 can exceed +30dBm), requiring high LO drive. Active mixers (Gilbert cell) provide conversion gain but lower linearity. Noise figure depends on conversion loss/gain and device noise contributions. Linearity analysis: Third-order products from RF nonlinearity set IIP3. Improvement techniques: LO signal optimization (fast switching reduces LO-feedthrough), Biasing for linearity (higher current improves IP3), Degeneration resistors, and Current-bleeding. Trade-offs exist between conversion gain, noise figure, linearity, and power consumption. Modern designs use complementary switching for flicker noise reduction.