2.1 mm-Wave 5G Radios: Baseband to Waves

There are many challenges in building millimeter-Wave (mmW) 5G radios [1] –[3]. Some of the key challenges are the cost, heat dissipation, and array calibration. This paper describes ADI’s full line-up of mmW 5G radios used today, with a focus on the millimeter wave front-end portion, and how it addresses some of these challenges. The radio block diagram, shown in Fig. 2.1.1, is an example of a dual-polarized 24-to-30GHz band mmW radio. All ICs in this radio cover 24 to 30GHz, allowing the same chips to be used in n257, n258, and n261 radios, which reduces the development cost. The radio consists of two domains: BB-IF and mmW. The BB-IF domain contains either an IF transceiver utilizing quadrature baseband data converters and mixers to generate the IF, or data converters (MxFE) to directly synthesize the IF. The former is optimal for narrower bandwidth applications while the latter consumes more power but can support higher bandwidths. The mmW domain consists of a mmW Up/Down converter and a 16-channel, (2 polarizations $\times 8$ channels per pol) high-performance beamformer (BF). The mmW chips utilize a 45nm RF SOI process, which is optimized for RF performance at the mmW 5G bands. The SOI process is a 12-inch process, hence economically suitable for large-volume applications. The BF linear output power is 12dBm/channel @ 3% EVM using a 400MHz 5G NR waveform. The channel P1dB is 20dBm. Two mmW BFs, cover 24-to-30 and 37-to-44GHz bands, respectively. An implementation of the mmW front-end, consisting of 128 dual-polarized antenna elements, 16 BFs, 4 Up/Down frequency converters (UDCs), and the power-management circuitry has been fabricated and is shown in Fig. 2.1.2. Over-the-air (OTA) measurement results of the fabricated array are presented below. The measurements include the radiation pattern, EIRP, linearity, and combined throughput of four streams. The paper also discusses the following: OTA Performance of ADI’s mmW 5G radios, antenna performance and design aspects, thermal aspects and heat dissipation modelling, and calibration of mmW radios.