NTT Develops World's First Ultra-Compact Baseband Amplifier IC Module with Built-in DC Block Function and 100GHz Bandwidth Performance

A Breakthrough Technology that Opens the Door to Next-generation, High-speed Communication and Measurement Applications

Tokyo - Feb. 23, 2023 - NTT Corporation (President and CEO: Akira Shimada, "NTT") has succeeded in developing an ultra-compact baseband amplifier IC module with an ultra-broadband performance of 100GHz. This technology is expected to be used in future all-photonics networks, namely IOWN and 6G, and fields achieving cutting-edge measurements since they will require an ultra-broadband signal amplification function⁴ rid of distortion

To achieve this breakthrough, NTT applied its InP-based heterojunction bipolar transistor (InP HBT) technology¹to improve the performance of amplifier ICs and package mounting technology to incorporate a DC block function² with 100 GHz bandwidth performance, realizing the world's first ultra-compact amplifier IC module. In addition, since NTT's development has a built-in DC block function and is ultra-compact, it can be directly connected to various devices, making it a highly usable module.

This result will enable ultra-high-speed optical communication in the next-generation IOWN network and cutting-edge measurement applications. Details of this technology were published online in IEEE Microwave and Wireless Technology Letters on (February) 16, 2023.

Research Background

The COVID-19 pandemic has accelerated the digital transformation of various services, so online communication traffic is exploding. NTT's core optical network, IOWN, will require transmission speeds of more than 2 terabits per second and a baseband amplifier IC module that can amplify the signal. In addition, in the areas of experimentation and measurement that support such advanced research, there is already a need for ultra-broadband and compact electric amplifiers, and the demand is increasing.

To date, NTT has developed a prototype of an ultra-broadband baseband amplifier IC module with a 1mm coaxial connector and has conducted the world's first demonstration experiment of optical transmission exceeding 2 terabits per second⁵. However, previous prototype modules were large and required external DC block parts to connect to the front and rear devices.

Research Achievements

By increasing the performance of amplifier ICs using InP HBT technology and advancing package mounting technology, NTT succeeded in realizing the world's first ultra-compact amplifier IC module that achieves both ultra-wideband performance of 100 GHz and DC block function integration (Figure 1).

Fig. 1: Comparison of conventional technology and this result

Ultra-broadband baseband amplifier IC based on InP HBT technology

NTT has achieved broad peaking characteristics (characteristics that emphasize gain on the high-frequency side) by further improving the performance of ultra-broadband baseband amplifier ICs⁶ using InP HBT technology developed by the company (Figure 2). This peaking characteristic makes it possible to compensate for high-frequency signal loss caused by package mounting and to ensure gain flatness (a characteristic in which a constant amplification factor is obtained from low frequencies to high frequencies) as an amplifier IC module.

Fig. 2: Baseband amplifier IC using InP HBT technology (a) Photo (b) Frequency characteristics

Ultra-broadband/ultra-small package mounting technology

NTT has ensured ultra-broadband characteristics by adopting a push-on type coaxial connector instead of the conventional thread-on type coaxial connector for the interface and devising the design of the joint between the coaxial and the internal high-frequency board. Also, researchers have achieved a drastic reduction in the size of the package. In addition, NTT made full use of precise high-frequency design technology to achieve DC block function integration (which was previously difficult to combine with ultra-wideband characteristics) by mounting a small thin-layer capacitor on the internal high-frequency substrate.

By combining these technologies, NTT achieved both ultra-broadband characteristics of 100 GHz or more and DC block function integration in an ultra-compact size with a volume ratio of less than one-tenth of conventional devices (Fig. 3). Finally, the researchers demonstrated that this amplifier IC module can amplify an ultra-wideband PAM-4 signal⁷ with a symbol rate⁸ of 112 gigabaud without distortion (Fig. 4).

Fig. 3: Baseband amplifier IC module (a) Configuration block diagram (b) Photo (c) Frequency characteristics

Fig. 4: Amplification experiment result of a 112 gigabaud PAM-4 signal generated by this amplifier IC module

Future Development

This result will be put into practical use at an early stage in applications where the need for ultra-broadband signal amplification has already become apparent, such as next-generation, ultra-high-speed optical communications and cutting-edge experimental and measuring instrument applications that support the research and development of 6G.

In the medium term, NTT will further improve their IC and package mounting technology and study application for ultra-high-speed optical transceivers in the next-generation IOWN network.

¹Heterojunction bipolar transistor using indium phosphide, a group III-V semiconductor. Transistor with excellent speed and withstand voltage.

²A function that removes the direct current (DC) component included in the signal. Essential to avoid device failures and malfunctions when connecting devices with different DC operating voltages.

³NTT R&D Website: "What's IOWN?" https://www.rd.ntt/e/iown/0001.html

⁴A signal of the information to be sent/received in communication. This baseband signal is carried on a carrier (carrier wave) and transmitted. A broadband for the baseband signal means that a large amount of information can be transmitted.

⁵NTT News Release: "NTT Achieves the World's Fastest Optical Transmission of over 2 Tbits/s Per Wavelength: A Large Capacity Communication Network Technology to Support IOWN & 6G"
https://group.ntt/en/newsrelease/2022/09/22/220922a.html

⁶NTT News Release: "NTT Achieves the World's Greatest Bandwidth of 241 GHz for an Amplifier IC: Enabling Ultra-High-Speed Device Technology for Next-Generation Data Centers and Beyond 5G"
https://group.ntt/jp/newsrelease/2019/06/03/190603b.html (Japanese only)

⁷4-level Pulse Amplitude Modulation (PAM) signal. A modulation method that can transmit 2-bit information per symbol by assigning 4-level signal states to 1 symbol.

⁸Represents the speed of modulation and indicates the number of modulations (waveform switching) per second. A 112 gigabaud signal means a signal with 112 billion modulations per second.

About NTT

NTT believes in resolving social issues through our business operations by applying technology for good. An innovative spirit has been part of our culture for over 150 years, making breakthroughs that enable a more naturally connected and sustainable world. NTT Research and Development shares insights, innovations and knowledge with NTT operating companies and partners to support new ideas and solutions. Around the world, our research laboratories focus on artificial intelligence, photonic networks, theoretical quantum physics, cryptography, health and medical informatics, smart data platforms and digital twin computing. As a top-five global technology and business solutions provider, our diverse teams deliver services to over 190 countries and regions. We serve over 75% of Fortune Global 100 companies and thousands of other clients and communities worldwide. For more information on NTT, visit https://www.rd.ntt/e/

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