A positive feedback passive mixer-first receiver front-end

This paper presents a technique to reduce the noise figure of a passive mixer-first receiver front-end. By using lower than 50Ω switch resistance in the current-mode passive mixer and introducing a positive feedback from baseband to the RF-input, it can be well matched close to fLO while achieving a noise figure below 3dB, which is otherwise a fundamental limit. A quadrature front-end prototype for a direct conversion receiver has been implemented in 65nm CMOS, occupying an active area of 0.23mm2 with a frequency operation ranging from 0.7 to 3.8 GHz. The prototype achieves a minimum noise figure of 2.5dB, an out-of-band 1dB compression point of +3dBm, with IIP3 and IIP2 exceeding +26 and +65dBm, respectively. The current consumption from a 1.2V supply is between 22.8 and 62.8mA, depending on frequency operation.