A Passive-Mixer-First Acoustic-Filtering Superheterodyne RF Front-End

Hyungjoo Seo, Jin Zhou

Research output: Contribution to journalArticlepeer-review


This article presents an agile passive-mixer-first superheterodyne RF front-end that utilizes a gigahertz acoustic filter as its intermediate-frequency (IF) load - essentially a mixer-first acoustic-filtering RF front-end. The passive mixer frequency-translates a sharp but fixed-frequency acoustic-filtering response to a much higher and mixer-clock-defined tunable frequency while preserves input matching, high linearity, and introduces minimal loss. In contrast to low- or zero-IF passive-mixer-first receivers which often use active filters at baseband, using an acoustic filter as the IF load is fraught with fundamental challenges. We introduce ON-chip LC tanks, as an impedance shaper, to suppress the acoustic filter impedance components at harmonic frequencies and an all-passive recombination network at IF to share one acoustic filter among multiple paths. Also, we extend the existing analysis of mixer-first front-ends from assuming a load impedance with a low-pass frequency response to having a generic load impedance. Our analysis unveils impedance aliasing in a generic mixer-first front-end, motivating the need for an ON-chip impedance shaper. A front-end prototype using a 65-nm CMOS switched- LC passive mixer followed by an off-the-shelf 1.6-GHz surface-acoustic-wave (SAW) filter is designed. In measurement, the RF front-end operates across 2.5-to-4.5 GHz achieving 5.5-dB noise figure and +29.4-dBm IIP3 at 1 × bandwidth offset.

Original languageEnglish (US)
Article number9391989
Pages (from-to)1438-1453
Number of pages16
JournalIEEE Journal of Solid-State Circuits
Issue number5
StatePublished - May 2021


  • Acoustic
  • Acoustics
  • bulk-acoustic-wave (BAW)
  • CMOS
  • filter
  • Impedance
  • interference
  • mixer
  • Mixers
  • N-path
  • Radio frequency
  • receiver
  • Receivers
  • Resonant frequency
  • Resonators
  • superheterodyne
  • surface-acoustic-wave (SAW).
  • surface-acoustic-wave (SAW)

ASJC Scopus subject areas

  • Electrical and Electronic Engineering


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