A 3–5-GHz, 385–540-ps CMOS true time delay element for ultra-wideband antenna arrays

Abstract

This paper proposes an all-pass filter-based true time delay (TTD) element covering a 3–5-GHz ultra-wideband (UWB) frequency. The proposed TTD element designed in a standard 0.18-µm CMOS technology achieves a tunable delay range of 385–540 ps with 6-ps delay steps and maximum 11% absolute delay error over a 3–5-GHz frequency band. It exhibits an average 3.6–4.6-dB noise figure (NF) within the whole bandwidth. A four-channel beamforming receiver realized by the proposed TTD element is designed and examined in this paper, as well. With the maximum delay of 540 ps and 6-ps average delay resolution, a maximum steering angle of ±45¿ with 5¿ (18 steps) steering resolution is demonstrated for the beamforming receiver with 2-cm antenna spacing.