Multiband operational receiver designed for 5G NR

Researchers from the Tokyo Institute of Technology (Tokyo Tech) have developed an ultrawide-band receiver based on a harmonic-selection technique, in order to improve the operational bandwidth of 5G networks. Their study, led by Professor Kenichi Okada, was published in the IEEE Journal of Solid-State Circuits.

As next-generation communication networks are being developed, the technology used to deploy them must also evolve. Fifth-generation mobile network New Radio (5G NR) bands are continuously expanding to improve the channel capacity and data rate. To realise cross-standard communication and worldwide application using 5G NR, multiband compatibility is essential.

Recently, millimetre-wave (mmW) communication has been considered a promising candidate for managing the ever-increasing data traffic between large devices in 5G NR networks. In the past few years, many studies have shown that a phased-array architecture improves the signal quality for 5G NR communication at mmW frequencies.

Unfortunately, multiple chips are needed for multiband operation, which increases the system size and complexity. Moreover, operating in multiband modes exposes the receivers to changing electromagnetic environments, leading to cross-talk and cluttered signals with unwanted echoes. To address these issues, Tokyo Tech researchers developed their novel harmonic-selection technique for extending the operational bandwidth of 5G NR communication.

“Compared to conventional systems, our proposed network operates at low power consumption,” Okada said. “Additionally, the frequency coverage makes it compatible with all existing 5G bands, as well as the 60 GHz earmarked as the next potential licensed band. As such, our receiver could be the key to utilising the ever-growing 5G bandwidth.”

To fabricate the proposed dual-channel multiband phased-array receiver, the team used a 65 nm CMOS process. The chip size was measured to be just 3.2 x 1.4 mm, which included the receiver with two channels.

The team took a three-pronged approach to tackle the problems with 5G NR communication. The first was to use a harmonic-selection technique using a tri-phase local oscillator (LO) to drive the mixer. This technique decreased the needed LO frequency coverage while allowing for multiband down-conversion. The second was to use a dual-mode multiband low-noise amplifier (LNA). The LNA structure not only improved the power efficiency and tolerance of the inter-band blocker (reducing interference from other bands) but also achieved a good balance between circuit performance and chip area. Finally, the third prong was the receiver, which utilised a Hartley receiver’s architecture to improve image rejections. The team introduced a single-stage hybrid-type polyphase filter (PPF) for sideband selection and image rejection calibration.

The team found that the proposed technique outperformed other state-of-the-art multiband receivers. The harmonic-selection technique enabled operation between 24.25 and 71 GHz while showing above 36 dB inter-band blocker rejection. Additionally, the power consumed by the receiver was low (36, 32, 51 and 75 mW at frequencies of 28, 39, 47.2 and 60.1 GHz, respectively).

“By combining a dual-mode multiband LNA with a polyphase filter, the device realises rejections to inter-band blockers better than other state-of-the-art filters,” Okada said. “This means that for currently used bands, the rejections are better than 50 dB and over 36 dB for the entire supported (24–71) GHz operation region. With new 5G frequency bands on the horizon, such low-noise broadband receivers will prove to be useful.”

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