A Linear Ultralow Flicker Noise Switched-Transconductance Downconversion Mixer

This article introduces a current-mode active double-balanced downconversion switched-transconductance (SwGm) mixer designed to address the adverse issues associated with partially up-converted flicker noise and second-order intermodulation (IM2) term in (SwGm) mixers. The proposed architecture swaps drain and source connections of transconductance (Gm) stage at each half cycle of the local oscillator (LO). The swapping, which results in a symmetrical Gmprofile with zero average value, is facilitated by series capacitors and ensures complete up-conversion of undesired low-frequency components. Compared to previous solutions, this method offers significant improvements, including a notably reduced flicker corner frequency and a better suppression of thermal noise. In addition, it eliminates the typical voltage headroom constraints caused by resistive loads. A proof-of-concept prototype mixer is fabricated in a 65-nm CMOS technology and operates at 6 GHz with an intermediate frequency (IF) bandwidth of 100 MHz. Experimental results demonstrate a competitive performance, including a 7-dB noise figure (NF) from 10 kHz to 100 MHz, a very low flicker corner frequency of 1 kHz, low power consumption of 3 mW from a 1-V supply, an 11.8-dB conversion gain (CG), average IIP2 and third-order input intercept point (IIP3) values of 75 and 0.9 dBm, respectively, and a compact layout of 0.396 mm2.