A 28-GHz Flip-Chip Packaged Chireix Transmitter With On-Antenna Outphasing Active Load Modulation

Abstract

This paper presents a packaged 28-GHz Chireix outphasing transmitter (TX) for power amplifier (PA) efficiency enhancement at both peak and back-off output power (PBO). The main objective is to investigate the possibility of employing a multi-feed antenna as a multi-port passive network to perform outphasing active load modulation. As a proof of concept, an outphasing TX architecture is proposed by leveraging a dual-feed loop antenna (DLA) to achieve high efficiency transmission of wideband complex modulated signals. Theoretical analysis and simulation results prove that the proposed DLA is electrically equivalent to an ideal differential series non-isolating power combiner, enabling superior on-antenna outphasing operation. Multi-functional signal processing is therefore achieved in a single loop-antenna footprint, including high-efficiency on-antenna power combining, outphasing active load modulation, and millimeter-wave (mm-Wave) signal radiation. Moreover, unlike conventional spatial vectorial combining techniques (e.g., spatial IQ or spatial outphasing), the antenna-level signal processing preserves the wide antenna unit field of view (FoV) and is particularly suitable for array or multiple-input-multiple-output (MIMO) applications. The proposed Chireix TX contains two phase-shifted sub-TXs simultaneously driving a DLA on package. The measurements demonstrate a 53%/43% PA drain/power-added efficiency (DE/PAE) at 17.1-dBm saturated output power ( $P_{\mathrm {sat}}$ ) and 36%/23% DE/PAE at 6-dB PBO. The high-efficiency Chireix TX supports up to 15 Gb/s 64-QAM with 10.4-dBm average output power and 34% average PA DE (19.2% average PAE) while maintaining EVM/ACLR better than −27.5 dBc/−28 dBc in a wireless radiation testing environment.