Design and Analysis of Enhanced Mixer-First Receivers Achieving 40-dB/decade RF Selectivity

• Published in: IEEE journal of solid-state circuits Vol. 55; no. 5; pp. 1 - 12
• Main Authors: Krishnamurthy, Sashank, Niknejad, Ali M.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 40-dB/decade roll-off; blocker resilience; Broadband; CMOS; high linearity; higher order impedance synthesis; Impedance; Integrated circuits; Linearity; low noise figure (NF) desensitization; Mixers; N-path filter; Noise measurement; Radio frequency; Receivers; Selectivity; Switches; Transfer functions
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2019.2956887

A ``second-order'' passive mixer-first receiver is proposed to improve channel selectivity, linearity, and noise figure (NF) in the presence of out-of-band blockers, by presenting an impedance that rolls off at 40 dB/decade as the load to an N-path filter. The synthesis of this impedance is described in a step-by-step manner starting from the required impedance transfer function to its actual circuit realization. Various tradeoffs and limitations of the architecture are described in detail, and layout-related techniques are also provided. Two integrated circuit prototypes were fabricated in 28-nm bulk CMOS as proof of concept for this circuit, including a low-power version. The receiver, capable of broadband operation from 0.2 to 2 GHz, achieves an out-of-band IIP3 of +33 dBm and a blocker P1dB of +12 dBm. Additionally, it achieves an NF of 4.4 dB with less than 2-dB degradation in NF for a 0-dBm blocker.