Interference-Tolerant Mixer-First Receivers for FR3: Design Principles and Tradeoffs

Abstract

Frequency Range 3 (FR3), spanning 7.125-24.25 GHz, is a promising candidate band for 6G communications, bridging the coverage of sub-6 GHz bands and the capacity of millimeter-wave frequencies. Its incumbent-dense and non-contiguous spectrum demands frequency-agile, interference-tolerant receivers (RXs) capable of hopping across fragmented sub-bands while withstanding strong blockers. Mixer-first RXs are well suited to this role, yet their design for FR3 has not been systematically addressed. This paper presents a hardware design perspective on mixer-first RXs for FR3, evaluating selectivity enhancement, harmonic rejection, linearization, low-noise design, and multi-phase clock generation under FR3-specific constraints. The analysis identifies viable techniques, fundamental limitations, and circuit- and architecture-level design tradeoffs. A central insight is that the frequency-translational property of mixer-first RXs allows selectivity, linearization, and noise cancellation to be implemented partly at baseband and translated to RF, enabling frequency-agile FR3 operation while shifting the dominant design constraints to mixer parasitics, baseband circuit robustness, and multi-phase clock generation.