An 800-ps Origami True-Time-Delay-Based CMOS Receiver Front End for 6.5–9-GHz Phased Arrays

A true-time-delay-based (TTD-based) receiver front end with 800-ps time delay for 6.5-9-GHz wideband phased arrays has been designed for satellite communication in a 65-nm CMOS technology. The proposed receiver front end consists of a balanced low-noise amplifier (LNA), a 6-bit attenuator with 15.75-dB tuning range, a programmable TTD element featuring 800-ps delay with 25-ps delay step, and an output buffer amplifier. A differential origami inductor is proposed to boost the delay unit's quality factor and mitigate the insertion loss introduced by the artificial transmission line (ATL). A current-mode radio-frequency (RF) multiplexer is designed to ensure a rapid delay switching. The receiver front end demonstrates a 3.6-dB noise figure (NF) with an 18-dB typical gain and an input 1-dB compression point (IP1dB) of -17 dBm at 6.5-9 GHz. This TTD element allows for a low insertion loss and a small chip area per unit time delay of ATL-based RF TTDs.

I. Introduction

The wideband phased array has gained increasing attention in satellite communications due to its high data rate and great efficiency. In a 64- to 128-element phased array with a antenna spacing, a 4–6 programmable frequency-independent delay is required to compensate the path delay difference among different elements, where is the wavelength. Phase-shifter-based (PS-based) arrays support high-resolution phase adjustment. However, they are not suitable for wideband applications with the beam-squinting issue [1] in a large array, especially when the delay difference is much larger than one period. Hybrid architecture can be used to support wideband applications shown as the front-end radio-frequency (RF) beamformer in Fig. 1, where the front PSs are responsible for fine delay adjustment and the following RF true-time-delay (TTD) elements serve as coarse delay adjustment. For an even larger array, digital beamforming can be added after signal downconversion and quantization of each RF beamformer to generate large-scale TTDs digitally. This forms multiple beams within the field of view (FoV) constituted by front-end analog beamformers simultaneously, as shown in Fig. 1. Although the front PSs can greatly relax the resolution requirements of the following RF TTD elements down to a quarter or half of the signal period, it is fairly challenging to achieve a low-loss passive large TTD, which is often associated with frequency dependency deteriorating array performance [2]. Fig. 1.

Hybrid wideband phased array architecture combining front phase shifters, RF TTD elements, and digital beamformer. The RF TTD elements are highlighted in red.