9 October 2017
FBH demos III-V electronics capability at Productronica, including InP and Si heterointegration
Berlin-based Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH) – which researches compound semiconductor-based electronic and optical components, modules and systems – is presenting a selection of current developments and advances of its power amplifiers, circuits and heterointegrated chips in hall B2, booth 317 at Productronica 2017 in Munich (14-17 November). FBH is exhibiting jointly with partners from the Fraunhofer Group for Microelectronics and fellow Leibniz institute IHP-Innovations for High Performance Microelectronics of Frankfurt (Oder), Germany.
FBH’s heterointegrated chips for terahertz applications, for example, combine the advantages of two technologies at the chip level: the high output power of indium phosphide (InP) with the complexity of silicon technology.
Further exhibits target digitalization and the future mobile communications standard 5G, including digital power amplifiers that offer efficient performance management and the highest flexibility simultaneously in addition to broadband operation.
Pushing frequency boundaries and combining advantages with heterointegrated chips
Regarding high-performance communications, frequencies in the subterahertz range are gaining increasing attention. To overcome the exponentially growing volume of short-range data traffic, wireless transmission routes are needed in the 100-500GHz band. Other applications in this band include materials testing, security technology for passenger and baggage screening, and high-resolution radar technology for intricate robotics applications.
All these system applications require electronic circuits that can deliver high output power in the sub-terahertz range, and they cannot be built using conventional semiconductor technology. Instead, FBH uses the InP for its integrated circuits. InP heterojunction bipolar transistors (InP-HBTs) can currently achieve cut-off frequencies of more than 500GHz (fmax) at a collector current of 20mA. The breakdown voltage lies above 4V, enabling high output power.
An industry-compatible process line for InP circuit wafers is being built at FBH in the scope of the German government Federal Ministry of Education and Research (BMBF) initiative Research Fab Microelectronics Germany (FMD), launched in April. This process line also allows FBH - together with IHP - to integrate InP circuits onto silicon-germanium (SiGe) BiCMOS technology. The high output power of InP can hence be combined with the complexity of silicon technology. Millimeter-wave and sub-terahertz modules can therefore be created on a single chip, which is paramount for portable and cost-effective system applications. This process is also offered to external customers as a foundry service.
Components for 5G
In preparing the technical infrastructure for 5G, hardware components must be made more efficient and more flexible, says FBH. This can be aided by increasing the degree of digitalization. Currently, the focus is on power amplifiers because they dominate the efficiency, and thus the operating costs, of the entire system.
Up to now, multiple separate modules have always been required to accommodate different communication standards and frequencies. FBH has therefore been working for several years on developing new digital amplifier architectures offering efficient power management, maximum flexibility, and broadband operation. The long-term goal is a fully digital transmitter in which one chip serves all frequency bands.
Complementary to this, FBH is researching powerful modulation and encoding methods, which largely determine the properties of digital amplifiers. It has already developed a novel modulator that can be built using conventional digital components. It also allows signals to be generated by all kinds of modulation methods.
FBH’s digital power amplifiers have already achieved competitive overall efficiency and linearity compared with established analog amplifier concepts such as Doherty. One recent power amplifier offers overall efficiency of more than 40% at 10dB PAPR (peak-to-average power ratio) in the range of around 1GHz.
Another method for digitalizing power amplifiers is discrete envelope tracking (ET). Modulating the supply voltage of the amplifier output stage ensures high power efficiency despite the strongly fluctuating instantaneous power of modern broadband modulation methods. Modulation is performed by switching the voltage back and forth only between a number of specific (discrete) constant voltages. This digitalized version of ET yields highly efficient broadband solutions. New records were recently achieved at FBH, namely a modulation bandwidth of 120MHz in a 75W amplifier at 1.8GHz. This ET concept can also be converted relatively easily for millimeter-wavelength amplifiers, as is crucial for 5G base stations.