A Broadband Mm-Wave VSWR-Resilient Joint True-Power Detector and Impedance Sensor Supporting Single-Ended Antenna Interfaces

Abstract

Mm-wave 5G communication seeks to support multi-Gb/s data-rates over its large available spectrum, particularly in the K/Ka bands (24 to 40GHz). To ensure sufficient link budget under mm-wave path losses, array-based systems are required. However, element coupling in practical antenna arrays varies each antenna load from its ideal <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$50\Omega$</tex> impedance (i.e., VSWR = 1). Power amplifiers (PAs) govern the overall transmitter (Tx) performance yet are the most susceptible blocks to VSWR variation, as they interface directly with antennas. The antenna VSWR alters the PA load, degrading the PA linearity, efficiency, output power, and reliability. Multiple proposed reconfigurable PAs maintain the PA performance under VSWR but require VSWR resilient built-in-self-test (BiST), particularly on-chip power and impedance sensors, to determine the PA operation/reconfiguration. Previous work on power detectors is primarily based on voltage sensing, which only tracks the true RF power for a fixed and known real load. The works in [1] and [2] detect both load current and voltage to measure the real RF power over VSWR. However, both only properly operate for differential PAs, while most mm-wave front-end/antenna interfaces require single-ended connections. Meanwhile, reported impedance detectors consist of either an equivalent passive series element or shunt element with large capacitive loading [3]–[5]. These designs inevitably add loss, limit the PA output-matching-network (OMN) bandwidth (BW), and change the OMN impedance transformation. The authors of [6] demonstrate VSWR-resilient joint power-and-impedance sensing at mm-wave but only at a single frequency. To overcome these issues, we demonstrate a single-ended broadband VSWR-resilient joint true-power/impedance sensor. While the proposed sensor is realized with and without an integrated PA on a Wilkinson power combiner (WPC) under both small- and large-signal CW operation, it can be applied on any single-ended RF/mm-wave signal trace and is agnostic to PA designs.