Origins of Intermodulation Distortion in A Pseudo-differential CMOS Beamforming Receiver

This paper studies the generation mechanisms of nonlinear distortion in the combination of an inverter-based LNTA and a passive mixer. The dominant nonlinearity appears to be the quadratic V _gs V _ds mixing term in the passive mixer, that first causes low-frequency IM2, and then up-converts it to IM3. It is found that adding a common-mode feedback cancels the IM2 in a pseudo-differential structure, and hence also reduces the IM3 caused by the cascaded second order nonlinearities significantly. The CMFB gain and bandwidth considerations and their effect on the results are also given, and it is concluded that from the linearity point of view, the feedback circuit does not have to be very wideband since the dominant distortion products originate from baseband.