This paper describes a direct up-conversion mixer. Basically, the proposed mixer inherits Gilbert's structure, but unlike the original Gilbert cell mixer, the transistors used as V-I converter operates in the linear region instead of in the saturation region to expand the input dynamic range up to $2 V_{pp}$. And the linearity is enhanced by the feedback loop. It has a LO buffer which amplifies the LO input signal and changes single input into a differential pair. This mixer was simulated with HPADS (HP Advanced Design System) and HSPICE. The spice model parameter of the transistor used is BSIM3 based on Anam 0.25 mm process. For the LO input of 0 dBm and the baseband input of $2 V_{pp}$, output power is -5.3 dBm and the wanted signal to the unwanted signal ration more than 30 dB. Output third order intercept point is 7 dBm and the output noise floor is -143 dBm/Hz. The total current consumption including OP-AMPs and the LO buffer is 20 mA at 2.5 V power supply.
