Fujitsu Makes a Terahertz Receiver Small Enough for a Smartphone

http://spectrum.ieee.org/tech-talk/telecom/wireless/fujitsu-makes-a-terahertz-receiver-small-enough-for-a-smartphone
By John Boyd

It’s a good time to be alive for pixel peepers. TV makers are pushing 4K-resolution sets to replace our present 1080p screens; Apple’s iMacs sport a 5K resolution; and NHK, Japan’s national broadcaster, is testing 8K broadcasting equipment, targeting 2020 and the Tokyo Olympics for its introduction.

To help wireless devices cope with the higher speeds demanded by such applications, Fujitsu has developed a 300-GHz prototype receiver compact enough to fit into a cellphone. Though limited to about 1 meter in range, the company says the device can download 4K and 8K video almost instantly.

Today’s cellphones operate in frequency ranges between 0.8 to 2.5-GHz, and are capable of download speeds of around 230 megabits per second, while the top speed for 802.11n Wi-Fi operating in the same frequency range can reach speeds as high as 600 Mb/s. Fujitsu touts its new receiver as operating in theterahertz band—frequencies of over 300 GHz—where terminals can communicate at speeds hundreds of times faster than today’s mobile handsets.

Devices to enable such high speeds have been developed, but because terahertz-band waves quickly attenuate, receiver-amplifier chips need to be sensitive enough to deal with a weak signal. Present designs rely on a separate antenna, which in turn requires a waveguide component to transport the incoming signal from the antenna to the chip. This makes the overall combination far too bulky for cellphone use, says Fujitsu.

The goal, then, is to create a receiver-amplifier module with a built-in antenna  to increase miniaturization. This has been achieved for devices employed in millimeter wave-band equipment operating at 60-GHz to 80-GHz frequencies, for instance, and used in applications such as collision-avoidance radar. These modules connect the antenna to the receiver-amplifier  chip through an internal printed-circuit substrate making a waveguide unnecessary.

Illustration: Fujitsu

“Typical printed-circuit-substrate materials used in these higher frequency ranges are ceramics, quartz ,and Teflon,” says Yasuhiro Nakasha, a research manager at Fujitsu’s Devices & Materials Lab. “But when these are used in terahertz-band communications, there is significant signal attenuation and loss of receiving sensitivity.”

To get round this, Fujitsu has micro-fabricated a printed-circuit substrate using a polyimide (a heat-resistant synthetic polymer) material.  Signals from the antenna are transmitted to the receiver-amplifier chip through a connecting circuit on the substrate.

In order to ensure stable signal transmission with low loss, the top and bottom faces of the printed circuit substrate are grounded and connected using through-hole metalized vias. This and the connecting circuit together form a grounded coplanar-waveguide structure: a transmission pathway designed to enhance high frequency signal propagation. To reduce signal interference from the printed circuit substrate, the vias need to be spaced apart less than one-tenth of the signal’s wavelength—in this case less than a few tens of micrometers.

Though the polyimide material experiences a signal loss ten-percent greater than quartz, Fujitsu says the material’s processing accuracy is more than four times higher than the latter. This makes it possible to space the vias closer together, thereby halving the overall signal loss compared to using a quartz substrate.

To facilitate a strong connection between the antenna connecting-circuit on the printed-circuit substrate and the receiver-amplifier chip, Fujitsu adapted a millimeter-mounting technology to handle terahertz transmission. This method let the receiver-amplifier circuitry directly face the printed circuit substrate.

The outcome is a module with an overall volume of just 0.75 cubic centimeters—not including output terminals—small enough to be incorporated into a mobile phone. Download speeds obtained so far in the lab reached 20 Gb/s.

Fujitsu will begin field-testing by the end of March 2016, and aims to launch the technology in 2020. The application the engineers envision include instant downloading of large volumes of data from servers and terminals, electronic versions of printed guides and brochures used at events, and downloading video and music from kiosks.

Nakasha isn’t looking beyond 2020 at the moment, but he believes the technology has the potential to one day achieve speeds of 100 Gb/s.

Part of the research used was obtained from an R&D project on expanding radio spectrum resources commissioned by Japan’s Ministry of Internal Affairs and Communications.

(Semi-OT) 240 GHz transceiver targets wireless applications

My Note: Just saw this posted on the Virginia Diodes Facebook page.

Boosting sensitivity tenfold with a new indium phosphide (InP) technology will enable millimetre-band, high-capacity reception for smartphones and other devices
http://www.compoundsemiconductor.net/csc/news-details.php?cat=news&id=19736921

Fujitsu Limited and Fujitsu Laboratories Ltd. have developed a high-sensitivity receiver chip that will pave the way to high-capacity, gigabit-capable wireless devices operating at 240GHz in the millimetre-wave frequency band.

This band refers to radio waves with frequencies from 30GHz to 300GHz.

The 240GHz band is a frequency range over 100 times wider than that used by typical mobile devices today (0.8 - 2GHz), which should enable a 100-fold increase in communications capacity. To achieve such an increase, however, requires amplifiers with high amplification ratios that can receive signals that have become very faint when transmitted through the air.

Given this, Fujitsu and Fujitsu Labs have developed a technology for multistage amplifiers that increases amplification ratios while suppressing an amplifier's oscillator effect, and a technology that efficiently transmits the amplifier's output signal to the next stage.

The result is that the receiver chip's sensitivity is increased roughly tenfold, making possible the reception of large data volumes by mobile devices using a compact antenna.

A portion of these research results was obtained through the, "R&D Program on Multi-tens Gigabit Wireless Communication Technology at Subterahertz Frequencies," a research program commissioned by Japan's Ministry of Internal Affairs and Communications as part of its "Research and Development Project for Expansion of Radio Spectrum Resources."

Background

The explosive growth of smartphones and other wireless devices has brought about an increase in the use of mobile data communications for browsing the web or downloading music, alongside conventional voice communication.

With an expected shift toward high-capacity data communications, including videos and movies, there is an expectation that demand will grow for devices that can instantly download such data.

In order for that to happen, high-capacity wireless devices will need to use wider frequency ranges than they do now.

Wireless devices that could use millimetre-wave frequencies would be able to take advantage of a frequency range 100 times wider than that used by today's wireless devices, so it is expected that they would also be able to handle communications speeds 100 times greater.

Millimetre-wave transmissions, particularly at such high frequencies as 240GHz, however, become severely attenuated as the radio waves travel through the air.

Receiving such a faint signal requires a highly sensitive receiver (comprised of an antenna, amplifier, and wave detector). The introduction of an amplifier with a high amplification ratio shows has been sought after as an effective way of improving reception sensitivity.

Technological Issues

A common way of increasing the amplification ratio of the amplifier is to connect multiple amplifiers as part of a staged construction, but more stages result in bigger chip sizes. When applying this technique in the 240GHz band, the wavelength of the signal is very short - less than 1 mm - so the length can be shorter than the chip itself, as shown in Figure 1.



Figure 1: Comparison of wavelengths

This creates technical problems that do not exist at the frequencies used by today's cellular phones (that use the 2GHz band). Output signals from the amplifier can leak to ground on the chip's surface, and these leaked signals return to the amplifier's input pin, resulting in double amplification as depicted in Figure 2 below.



Figure 2: Signal leakage through ground

When the leaked signal re-enters the amplifier, it is amplified again and produces even more signal leakage, which returns to the input pin yet again, creating what is known as the oscillator effect, making it difficult to receive these signals correctly. For this reason, creating a high amplification ratio with millimetre waves requires a technology that can suppress these oscillations without losing amplification levels.

About the New Technology

The device builds on InP HEMT technology developed by Fujitsu and Fujitsu Labs.

The original InP HEMT device invented in 1979 by Fujitsu Laboratories' researcher Takashi Mimura (currently a Fellow at Fujitsu Laboratories), is a transistor made of compound semiconductors featuring excellent speed and noise characteristics. Using an InP substrate results in higher speed and lower noise than with conventional gallium-arsenide. In addition to high-speed communications, it is expected to be applied in millimetre-wave image sensors.

The latest technology uses a multistage amplifier that suppresses the oscillator effect while increasing the amplification ratio.

Also developed was an impedance-matching technology that efficiently conveys the output signal from one stage to the next. This produces a roughly tenfold improvement in receiver-chip sensitivity over previous designs. Key features of the technology are as follows.

1. Multistage amplifier suppresses oscillator effect, increases amplification ratio

The leaked signal from an amplifier will always have "antinodes" at specific sites where that signal is at its greatest amplitude, and "nodes" where it has no amplitude at all. If the amplifier's input pin is located in a leaked signal's antinode, then a stronger leaked signal will feed back into the amplifier, creating the oscillation effect (Figure 3, top). Conversely, if the input pin is located in a node, the leaked signal has no amplitude, and the amplifier will not re-amplify the leaked signal.

Fujitsu has aligned the input pin and output pin with the nodes in the leaked signal (Figure 3, bottom). Connecting amplifiers designed this way into multiple stages results in high amplification ratios without an oscillator effect.

2. Impedance-matching technology efficiently transmits amplifier output signal to next stage

Efficiently transmitting the output signal from an amplifier to the next stage requires impedance matching on the lines that connect the amplifiers, which, in turn, requires that the lines be of a uniform length.

But aligning the input and output pins of the amplifiers with the nodes limits the dimensions of the amplifier, while the length requirements on the lines create another set of constraints, complicating the task of impedance matching.

To resolve this problem, a U-shaped line was deployed and the length and width of the U were adjusted to enable impedance matching regardless of the limitations on the dimensions of the amplifier.

located in a leaked signal's antinode, then a stronger leaked signal will feed back into the amplifier, creating the oscillation effect (Figure 3, top).

Conversely, if the input pin is located in a node, the leaked signal has no amplitude, and the amplifier will not re-amplify the leaked signal. Fujitsu has aligned the input pin and output pin with the nodes in the leaked signal (Figure 3, bottom). Connecting amplifiers designed this way into multiple stages results in high amplification ratios without an oscillator effect.



Figure 3: A conventional amplifier and the newly-developed amplifier

Results

These technologies have produced a roughly tenfold improvement in the sensitivity of a receiver chip compared with previous designs. These receivers could be used in smartphones and other wireless devices equipped with compact antennas. And because this would also allow for antennas with broader relative directionality(4) than existing devices, there would be no need to precisely align the transmitter to the handset (Figure 4), resulting in greater convenience for users.



Figure 4: Scenario showing handset in use

Future Plans

Fujitsu is working to develop a compact package that integrates an antenna along with a receiver chip based on this technology, with the goal of conducting transmission testing by sometime in 2015 and practical applications around 2020.

Fujitsu : Develops Terahertz-Band Imaging Method Speeding Up Material Inspections 25-Fold

September 12, 2011

Fujitsu Laboratories Ltd.

Makes interiors of objects visible; safer than X-rays, can be applied to a wider range of materials

Kawasaki, Japan, September 12, 2011 — Fujitsu Laboratories Limited today announced that it has developed a technology that will speed inspections that use terahertz-band imaging by a factor of 25. Terahertz waves, which can penetrate non-metallic materials such as paper, plastic, and textiles for nondestructive inspections, hold the promise of showing an accurate picture of a subject, revealing hidden materials through non-destructive inspections, and making an object's interior visible. Existing terahertz-wave inspection methods have only been able to measure a part of a substance per exposure. Obtaining a complete picture of a target object has required incrementally shifting the target between repeated exposures, resulting in a time-consuming process.

Fujitsu Laboratories has developed a new optical element that obviates the need for moving the target, measuring 30 millimeters both horizontally and vertically, by reducing its inspection time from 34 minutes to 1 minute and 21 seconds - speeding up the process by a factor of 25. As a result, this new technology has potential applications in airport security, inspecting narcotics in envelopes, and inspecting electronic devices.

Background

Terahertz waves have a wavelength of approximately 0.3 mm, lying on the spectrum of electromagnetic radiation between light waves and radio waves, and can penetrate non-metallic substances such as paper, plastic, and textiles. Similar to how objects look different under X-rays and visible light, the use of terahertz waves reveals objects in a different way. A specific item can be identified by its characteristic spectrum (a "fingerprint spectrum") under terahertz waves. As well, compared to X-rays, terahertz waves are deemed safe for people. On the other hand, as terahertz-wave imaging has far been a time-consuming process, it has had a limited range of applications. However by taking advantage of the ability to make visible what had been invisible, the use of terahertz waves holds promise in applications that make the inside of objects visible. This includes customs inspections without the need to open luggage or packages, inspections of the contents of envelopes, inspections of adulterants in foodstuffs, and quality inspections of electronic devices.

Technological Issues

The problem with terahertz-band imaging has been the time required to scan the contents of carry-on luggage, for example.

Terahertz waves are not visible to the eye and cannot be photographed. As shown in Figure 4, an electro-optical crystal(1) makes it possible for variations in the strength of a terahertz wave to be photographed indirectly, by modulating them to changes in the light intensity of a probe light. It has been proposed that inspection methods using these crystals could be accelerated by exposing the target object to terahertz waves at the same time that it is exposed to an angled probe light. By taking advantage of the time difference between the penetrating terahertz wave and the probe light, the time waveform of the penetrated target material could be instantly obtained.

However as this process can only receive information on one direction of the substance from one exposure, it is not possible to measure the complete substance in one exposure. To obtain a complete picture requires incrementally shifting the substance between repeated measurements.

About the New-Developed Technology

To measure the object without moving it, Fujitsu Laboratories developed an improvement to the technique using a terahertz wave and angled probe light beam in which a newly-developed graduated mirror array with multiple levels is placed in the light beam. As this technique produces results equivalent to those obtained when taking multiple exposures with incremental movements between each, it becomes possible to perform an inspection with just one exposure.

Results

Fujitsu Laboratories researched terahertz-band imaging using this graduated mirror array and found that measurement times were 25 times faster, reducing the time frame from the previous 34 minutes to 1 minute and 21 seconds, for targets measuring 30 millimeters horizontally and vertically. This new technology has the promise to accelerate airport-security inspections, inspections for narcotics in envelopes, and electronic-device inspections.

Future Plans

Fujitsu Laboratories is continuing to work on even faster methods, with an eye towards commercialization around 2014, and is proceeding with development for applications in manufacturing inspections.

Glossary and NotesA crystal whose optical refractivity varies with the intensity of terahertz waves incident upon it. The crystal modulates a probe light beam shone upon it, effectively modulating the terahertz waves into changes in intensity in the probe light beam, which can be recorded by a camera.About Fujitsu Laboratories

Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited is one of the premier research centers in the world. With a global network of laboratories in Japan, China, the United States and Europe, the organization conducts a wide range of basic and applied research in the areas of Next-generation S