A Fully Passive RF Front-end with 13 dB Gain Exploiting Implicit Capacitive Stacking in a Bottom-plate N-path Filter/Mixer

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Abstract—A low-power interferer-robust mixer-first receiver front-end that uses a novel capacitive stacking technique in a bottom-plate N-path filter/mixer is proposed. Capacitive stacking is achieved by reading out the voltage from the bottom-plate of N-path capacitors instead of their top-plate, which provides a 2x voltage gain after down-conversion. A step-up transformer is used to improve the out-of-band (OOB) linearity performance of small switches in the N-path mixer, thereby reducing the power consumption of switch drivers. This paper explains the concept of implicit capacitive stacking and analyzes its transfer characteristics. A prototype chip, fabricated in 22nm FDSOI technology, achieves a voltage gain of 13 dB and OOB IIP3/IIP2 of +25=+66dBm with 5 dB Noise figure while consuming only 600 _W of power at fLO=1 GHz. Thanks to the transformer, the prototype can operate in the input frequency range of 0.6-1.2 GHz with more than 10 dB voltage gain and 5–9 dB Noise figure. Thus it opens up the possibility of low-power software defined radios.
Original languageEnglish
JournalIEEE journal of solid-state circuits
Early online date27 Dec 2019
Publication statusE-pub ahead of print/First online - 27 Dec 2019



  • bottom plate mixing
  • capacitive stacking
  • CMOS
  • N-path filter
  • mixer-first receiver
  • Internet of Things (IoTs)

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