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RF Low Noise Amplifier Technology Landscape Grows More Diverse

Parent Category: 2019 HFE

By Tim Galla

Abstract

RF low noise amplifiers (LNAs) fabricated with solid state technology have been in use for several decades. The early transition to solid state was pioneered with germanium, has subsequently transitioned to silicon, and has now expanded to include a wide range of compound III-V semiconductors and new carbon-based materials. The rapid adoption and advancement of LNA technologies is largely do the growth and diversification of RF applications, and the specific requirements for these new and varying use cases. These requirements include the recent focus of greater linearity demands that complex modulation schemes for 5G applications pose on receivers at millimeter-wave frequencies, large-scale deployments of automotive radar, adoption of beam steering/antenna arrays, and advancements in low-probability-of-detection/low-probability-of-intercept (LPD/LPI) and high survivability radars.

Introduction

Evolving from the early germanium transistors, modern low noise amplifiers (LNAs) are fabricated using compound semiconductors with heterojunctions and even new carbon materials. The effort and advancement in LNA device technology is driven by a growing need for LNAs with specific performance parameter improvements for the many, and growing, receiver and signal chain applications seen today. Balancing factors of cost, availability, ruggedness, noise figure, bandwidth, power consumption, gain, and linearity is bringing about more innovations with LNA technology than seen before. However, there are also well established LNA technologies that are evolving to compete with these new technologies, or are so well depreciated they still hold a strong lead in cost efficiency.

Key RF LNA Device Technologies

  • Silicon Germanium (SiGe)
    • Silicon Germanium Bipolar Complementary Metal Oxide Semiconductor (SiGe BiCMOS)
    • Silicon Germanium: Carbon (SiGe:C)
  • Gallium Arsenide (GaAs)
    • Aluminum Gallium Arsenide AlGaAs/GaAs
  • Gallium Nitride (GaN)
    • Aluminum Gallium Nitride (AlGaN/GaN)
  • Indium-based
    • Indium Phosphide (InP)
    • Indium Aluminum Phosphide (AlInP/InP)
    • Indium Arsenide
  • Silicon
    • RF CMOS
    • Silicon-on-insulator (SoI)
    • Bipolar CMOS (Bi-CMOS)
  • Carbon Nanotube (CNT)

This article provides an overview of current RF LNA device technologies and discussion of the trends and applications of these technologies. Some explanation is also provided of the common variants of these technologies.

 1912 HFE LNA fg01

Figure 1 • A comparison of the highest frequency capability of several transistor technologies considered for terahertz applications. (Source [1.3]) https://www.mdpi.com/sensors/sensors-19-02454/article_deploy/html/images/sensors-19-02454-g001-550.jpg

Silicon Germanium (SiGe) for RF LNAs

SiGe bipolar complementary metal oxide semiconductor (BiCMOS) technology is for a wide range of RF applications, as well as digital/analog applications.These include LNAs, frequency synthesizers, filters, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), transceivers, and voltage controlled generators. The breadth of use of SiGe technology stems from its cost, which is relatively close to silicon for RF applications, and that the production and process technology of developing SiGe transistors isn’t substantially different from that of producing conventional silicon transistors (much of the same infrastructure can be used). SiGe transistors are also used in cryogenic applications, due to their wide operating temperature capability.

Commonly, SiGe heterojunction bipolar transistors (HBTs) are the type of transistor used for high frequency and high performance applications. This includes devices that operate to a significant fraction of a terahertz [1.3]. The most common application, historically, for SiGe technology has been in cell phone receivers, as the combination of low noise and wide dynamic range in the cellular spectrum (700 MHz to 3 GHz) compared to conventional silicon made this technology more viable [1.4].

Advantages of SiGe LNAs over CMOS LNAs [2.1, 2.2]

  • Lower inherent noise
  • Better input match for optimized gain
  • Improved gain/noise figure trade-off
  • Better linearity (higher dynamic range)
  • Possibility of die size advantages at innate input match is superior and additional on-chip inductors aren’t needed
  • SiGe BiCMOS brings the best of both worlds
  • Operation well into millimeter-wave and sub-millimeter wave frequencies

Silicon Germanium:Carbon (SiGe:C)

With the addition of carbon to SiGe heterojunction transistors, even more control of a silicon transistor’s band-gap is possible. Moreover, with added carbon, SiGe:C HBTs have demonstrated lower noise figure, higher collector current, higher unity gain frequency, and better linearity than Si BJTs. In essence, SiGe:C provides the advantages of SiGe with even greater maximum frequency and lower noise figure while still maintaining compatibility with mainstream silicon fabrication process. Hence, SiGe:C BiCMOS processes are capable of producing cost effective and still high performance wireless device chips, including complete Systems-on-Chip (SoCs) for applications such as Bluetooth, wireless data links, 3G/4G LTE, 5G low-/mid-/high-band, WiFi, automotive radar, and fiber optic drivers.

1912 HFE LNA fg02 

Figure 2 • Comparison of noise figure versus frequency of several LNA technologies (circa. 2012 [1.1]) https://drive.google.com/open?id=1mIpJmjjdtWkQJwew9WQhjmpzQJFnD6Fa

Gallium Arsenide (GaAs) for RF LNAs

With advances in semiconductor processing technologies that include metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), compound semiconductors based on III-V materials deposited in this layers became possible. Thus GaAs substrates and AlGaAs/GaAs high electron mobility transistors (HEMT) were born and found use in a wide range of high performance, frequency, and bandwidth applications. One of the main advantages of AlGaAs/GaAs HEMTs is an increase in bandgap over GaAs of 1.4 eV to 1.8 eV.

Further advances led to the development of Pseudomorphic HEMTs (pHEMTs), which required the use of InGaAs material to increase the electron mobility in the 2-dimensional region, with the result of yielding higher transconductance.

However, lattice mismatch and the mechanical strain of using Indium sets a limit of roughly 30% Indium concentration, limiting the overall potential performance increase from the pHEMT design. Innovation of an additional InAlGaAs buffer layer and a graded Indium concentration to achieve better lattice constant match with the GaAs substrate and InGaAs channel, led to the development of ever higher frequency and lower noise performing metamorphic HEMT (MHEMT) devices. MHEMTs made with GaAs substrates are generally lower cost, benefit from Gallium’s higher crystal quality, have better mechanical strength, and have a larger 6” wafer size compared to Indium substrates.

In industry, GaAs HEMT, pHEMT, and mHEMT processes are all used to make practical and high performance LNAs. These devices. Generally, for upper microwave and millimeter-wave frequencies, pHEMT and mHEMT transistors are used instead of standard HEMTs. Hence, there are ultra-wide bandwidth (UWB) GaAs LNAs that operate to several gigahertz, tens of gigahertz, and to hundreds of gigahertz. There are also many GaAs LNA technologies that have been approved/certified for use in space as well as aerospace vehicles. GaAs LNAs, power amplifiers (PAs), and transmit/receive (TR) modules are commonly used in many aerospace, defense, and security (ADS) applications, as well as automotive, cellular, and is being evaluated for upcoming 5G small cells and handsets [3.1].

GaAs technologies are some of the most widely used for LNA applications due to GaAs good noise figure performance, reasonable gain and power, as well as balance of cost and technological maturity. GaAs LNAs typically have a higher noise figure than InP and tend not to operate to as high frequency (with the exception of some GaAs MHEMTs). Moreover, GaAs LNAs tend to have a lower noise figure than GaN, but have a much lower maximum operating voltage.

Indium Phosphide (InP) for RF LNAs

InP LNAs are generally considered some of the lowest noise figure and highest frequency performance LNAs. Much like with GaAs HEMTs, and pHEMTs, layers of InAlAs and InGaAs are placed on an InP substrate to develop high bandwidth and high frequency transistors. Also similar with GaAs LNAs, UWB LNAs are often developed in cascaded or distributed approaches that achieve low noise figure over tens of gigahertz of bandwidth. These types of LNAs are sometimes called low noise distributed amplifiers (LNDAs). InP HEMT transistors are sometimes fabricated on substrates, such as silicon carbide (SiC) for high voltage and high power applications, and SiC exhibits better thermal conductivity performance than InP substrates.

InP HEMT transistors can typically handle higher voltage and power than GaAs transistors, especially at higher frequencies. However, InP technologies are more expensive and are generally less widely used than GaAs HEMTs. InP LNAs are common in test and measurement equipment, radio astronomy, highly sensitive radar, fiber optic receivers, cryogenic sensors and other applications that require the lowest noise figure and highest frequency. These applications include LNAs that operate from several gigahertz and into the terahertz range.

More recent research of InP LNAs involves the development of double HBTs (DHBTs). DHBT processes exhibit a wider bandgap and higher breakdown voltage compared to HEMT devices, which is desirable for high power and high frequency applications, but also distributed LNAs [4.1].

Gallium Nitride (GaN) for RF LNAs

GaN is a widely hyped and emerging transistor technology that is finding use in high power and high frequency applications in virtually all microwave and millimeter-wave applications. GaN devices exhibit a very high breakdown voltage and power density capability that far exceeds GaAs and InP. Hence, GaN devices are most often used in PA applications.

However, there are some cases in which receivers experience high input powers. In these cases, limiters are added to the input of the LNA, which intrinsically reduces both noise and bandwidth performance of the receiver. These applications typically include receivers that experience jamming or high levels of interference (solar storms/cosmic radiation). An alternative is to use GaN-based LNAs with much higher input power capability, while still offering good noise figure features. GaN LNAs have been reported to survive input power levels over 30 dBm continuous wave (CW) and nearly 50 dBm pulsed [5.1]. Moreover, extremely high linearity GaN LNAs have also been demonstrated with third-order output intermodulation points (OIP3s) around 40 dBm [5.1]. Both GaN HEMT LNAs and GaN FET LNAs have been studied for the purpose of developing high-survivability LNA technology.

Silicon (RF CMOS/SOI/BiCMOS) for RF LNAs

Stressing cost efficiency and compatibility with existing semiconductor manufacturing and processing infrastructure, there are a wide range of various Si-based transistor technologies that can be used to make RF LNAs. This includes silicon-on-insulator (SoI) technologies, which are now a significant contributor to cellular user equipment (UE). GaAs and RF SoI are competing technologies for 4G and upcoming 5G technologies, but still lacks GaAs in transmitter and receiver performance [6.1].

However, Si-based LNA technologies do benefit from enhanced integration with other components, devices, and domains, which enables the realization of complete RF front-end modules (FEM) systems-on-chip (SoC). As a consequence of Si-based LNA integration and cost efficiency, there are many CMOS and SoI technologies used commercial products, such as Bluetooth, WiFi, Zigbee, Cellular, and other Internet-of-things (IoT) modules, as well as part of larger SoCs and ICs with integrated wireless modules.

Generally, Si-based LNA applications operate to a maximum of several gigahertz. In some cases, advanced SoI and CMOS technologies are being pioneered for millimeter-wave frequencies in anticipation of upcoming millimeter-wave 5G user equipment, handsets, and base stations in addition to potentially reducing costs of millimeter-wave radar used in automotive driver-assist systems.

Carbon Nanotubes (CNTs) for RF LNAs

For several years there has been the hope of developing carbon-based transistors that can compete with semiconductors that are more expensive or are limited resources. Recently, there has been innovation in the use of carbon-nanotube (CNT) transistors that can operate to millimeter-wave frequencies [7.1,7.2]. In one example, CNT FETs were developed that demonstrate high inherent linearity and may potentially be used to realize future high frequency and wide bandwidth LNAs [7.1].

Conclusion

LNAs are key devices in virtually all RF systems. Depending on the needs of a technology there are now a wide-range of semiconductors and device technologies to choose from. The end-performance of these LNAs depends largely on the inherent properties of the semiconductor, as well as the device type and design of the LNA circuit. This article provided a brief overview of modern LNA technologies, as well as mentioned potential upcoming carbon-nanotube technologies with high inherent linearity that may be used to build future LNAs with extreme linearity.

About the Author

Tim Galla serves as Product Manager at Pasternack.

References

1.General

  1. Niehenke., E. C. (2012). The evolution of low noise devices and amplifiers. 2012 IEEE/MTT-S International Microwave Symposium Digest. doi:10.1109/mwsym.2012.6258248
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6603590/
  3. https://www.mdpi.com/1424-8220/19/11/2454?type=check_update&version=2

2. Circuits at the Nanoscale: Communications, Imaging, and Sensing edited by Krzysztof Iniewski

  1. 2.Silicon Germanium RF Low Noise Amplifiers
  2. https://iopscience.iop.org/article/10.1088/1361-6641/aade64/pdf
  3. https://iopscience.iop.org/article/10.1088/1757-899X/475/1/012002/pdf

 

3.Gallium Arsenide RF Low Noise Amplifier 

  1. https://www.businesswire.com/news/home/20190610005586/en/Global-China-GaAs-Industry-Report-2019-2025-Skyworks

4. Indium Phosphide RF Low Noise Amplifiers

  1. Shivan, T., Kaule, E., Hossain, M., Doerner, R., Johansen, T., Stoppel, D., … Rudolph, M. (2019). Design and modeling of an ultra-wideband low-noise distributed amplifier in InP DHBT technology. International Journal of Microwave and Wireless Technologies, 1–10.

5.Gallium Nitride RF Low Noise Amplifiers

  1. https://www.researchgate.net/publication/3131743_Analysis_of_the_Survivability_of_GaN_Low-Noise_Amplifiers

6. Silicon RF CMOS RF Low Noise Amplifiers

  1. http://soiconsortium.eu/wp-content/uploads/2018/08/Costa-RFSOI-Symposium-Shanghai-2018-final-distribution.pdf

7. Carbon Nanotube RF Low Noise Amplifier

  1. Maas, S. (2017). Linearity and dynamic range of carbon nanotube field-effect transistors. 2017 IEEE MTT-S International Microwave Symposium (IMS)
  2. Cao, Y., Che, Y., Gui, H., Cao, X., & Zhou, C. (2015). Radio frequency transistors based on ultra-high purity semiconducting carbon nanotubes with superior extrinsic maximum oscillation frequency. Nano Research, 9(2), 363–371. doi:10.1007/s12274-015-0915-7

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