A 33.5–37.5-GHz Four-Element Phased-Array Transceiver Front-End With Hybrid Architecture Phase Shifters and Gain Controllers

To satisfy the requirements for a high output power of the transmitter (TX) and high-quality beamforming with a wide range, fine resolution, high accuracy, and good orthogonality, in this work, we present a 33.5–37.5-GHz four-element phased-array transceiver front-end with two-way power combining power amplifiers (PAs), high-linearity low-loss stacked T/R switches, hybrid architecture phase shifters, and hybrid architecture gain controllers in a 65 nm CMOS process. The hybrid architecture phase shifter combines a reflection-type phase shifter (RTPS) with a 0°/180° phase switch. The RTPS provides a 180° phase shift (PS) range, and the 0°/180° phase switch expands the 0°–180° PS states into a full 360°. The hybrid architecture gain controller combines a 4-bit digital-step single-pole-double-throw (SPDT)-only attenuator with a two-stage 3-bit cascode variable gain amplifier (VGA). The attenuator generates large attenuation states for coarse-tuning, and the VGA generates small gain states for fine-tuning. The proposed phased-array transceiver front-end achieves a $P_{\mathrm {sat}}$ of 19.8 dBm and an OP $_{\mathrm {1\,dB}}$ of 17.2 dBm per element, a 6-bit full 360° PS range with an rms phase error lower than 2° and a gain variation lower than ±2 dB, and a 6-bit 0–31.5 dB gain control range with an rms gain error lower than 0.16 dB and a phase variation lower than ±3°.

I. Introduction

Millimeter-wave (mm-wave) phased arrays for fifth-generation (5G) communication, radar, and satellite communication systems have obtained ever-increasing attention. Phased arrays enable electronically steerable beamforming, and thus, provide higher effective isotropic radiated power (EIRP) in transmitters (TXs) and better signal-to-noise ratio (SNR) in receivers (RXs) [1], [2]. For these potential application scenarios, a phased-array transceiver front-end must satisfy some critical performance requirements, as shown in Fig. 1. First, a high output power of the TX supports long-range communications and radar detection, making the power amplifier (PA) one of the most critical components in a phased-array transceiver front-end. Second, the T/R switch at the antenna port must have high linearity and low insertion loss (IL) to handle the large output power from the PA. Third, high-quality beamforming relates to 1) a wide range (phase shift (PS) range or gain control range), 2) fine resolution (minimum PS or gain control step), 3) high accuracy (evaluated as the rms phase/gain error compared to intended steps), and 4) good orthogonality of PS and gain control. This makes phase shifters and gain controllers crucial components in a phased-array transceiver front-end. The range, resolution, and accuracy of PS and gain control directly translate to beam steering range, resolution, and accuracy. Orthogonality is, however, often missed but is also of great importance. Beam steering and sidelobe suppression are directly determined by the phase shifter, which enables beam steering, and the gain controller, which achieves sidelobe suppression through tapering [3]. From a system perspective, it is imperative to achieve orthogonal beam steering and sidelobe suppression functions, which correspond to orthogonal PS and gain control in a phased-array transceiver front-end [4]. Correspondingly, from a circuit perspective, the PS and gain control in each element must be orthogonal as well. This circuit-level orthogonality requires the phase shifter to present a low gain or loss variation over different phase settings and the gain controller to present a low phase variation over different gain settings. Fig. 1.

Block diagram of a typical phased-array transceiver front-end and performance requirements for critical components.