A Capacitive Stacking Mixer-First Receiver With Higher Order Capacitive Feedback

This article presents a capacitive stacking mixer-first receiver (MF-RX) with a higher order capacitive feedback (CFB) loop designed to increase interferer rejection right at the mixer baseband (BB) node, benefiting both the out-of-band (OOB) linearity of the passive mixer switches and the active BB circuitry. The CFB loop consists of a left-half-plane (LHP) and right-half-plane (RHP) zero together with an OOB complex pole pair so as to transition in-band (IB) positive feedback into stronger OOB negative feedback, resulting in a steep closed-loop (CL) filtering slope of -15 dB/octave. Using a normalized BB model, the CFB loop is implemented on the system level while a dual-path approach is introduced to map the system to the schematic level. A prototype of the MF-RX is realized in 22-nm fully depleted silicon-on-insulator (FDSOI) technology and achieves an adjacent-channel third-order intercept point (IIP3) of over 18 dBm across the wide 1.2–7.2-GHz local oscillator (LO) range as a direct result of the improved selectivity. The design achieves a channel bandwidth (BW) of 40 MHz, while the total radio frequency (RF)-to-BB gain is 32 dB. The 2× passive voltage gain of the capacitive stacking MF-RX enables a static power consumption of 9.7 mW at a minimum double sideband (DSB) noise figure (NF) varying from 5.1 to 9.0 dB across the LO range.