Abstract
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 $\times $ bandwidth offset.
Highlights
T HE ever-increasing demands on wireless communications and sensing have been making electromagnetic (EM) spectrum, the portion that is below 6 GHz, highly sought-after and congested
We have demonstrated a mixer-first acoustic-filtering superheterodyne RF front-end
It represents a new reconfigurable RF receiver architecture that fuses the strength of a widely-tunable passive-mixer-first front-end with the advantage of high-selectivity acoustic filters, while compensates for their respective bottlenecks, namely tight trade-off among the noise, linearity, and bandwidth in CMOS and the lack of frequency tuning in acoustics
Summary
T HE ever-increasing demands on wireless communications and sensing have been making electromagnetic (EM) spectrum, the portion that is below 6 GHz, highly sought-after and congested This makes RF filtering that suppresses strong out-of-band (OOB) interference indispensable. Acoustic filters using surface-acoustic-wave (SAW) and bulk-acoustic-wave (BAW) technologies are deployed for many modern commodity mobile devices because of their low loss, steep filter transition band roll-off, high linearity, and compact form factors [1]. These acoustic filters generally cannot be tuned across a wide frequency range and have somewhat fixed and pre-defined operation frequencies.
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