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.

Testing Automotive Radar Brings mm-Wave Challenges

My Note: Thanks to Virginia Diodes for sharing this article on their facebook page.

Automotive radar systems at 77 GHz are bringing a great deal of safety functions to lower-costing vehicles, but their manufacturers and suppliers are in need of cost-effective measurement solutions.

Oct. 15, 2013 Jack Browne

http://mwrf.com/test-amp-measurement-analyzers/testing-automotive-radar-brings-mm-wave-challenges?page=1

Automotive applications are requiring increased use of RF/microwave frequency bands, from low RF signals through millimeter-wave frequencies at 77 GHz. As these high-frequency signals become more integral parts of the worldwide driving experience, effective test solutions become more critical for designers developing new automotive RF/microwave circuits, as well as production facilities seeking efficient methods for verifying the performance of these added circuits. While lower-frequency testers are in abundance, and automotive applications employ a wide range of wireless frequencies—including remote keyless entry (RKE) systems at 433 and 868 MHz—a growing concern in automotive markets is for the accurate and cost-effective testing of 77-GHz automotive radar systems. This interest stems from the fact that historically, measurement equipment at such high frequencies has neither been commonplace nor cost-effective.
A number of different automotive radar-based safety applications make use of frequencies from 76 to 77 GHz, for adaptive cruise control (ACC), blind-spot detection (BSD), emergency braking, forward collision warning (FCW), and rear collision protection (RCP). For example, in a collision warning system, an automotive radar sensor can detect and track objects within the range of the transmitted and returned radar signals, automatically adjusting a vehicle’s speed and distance in accordance with the detected targets. Different systems can provide a warning of a potential collision ahead and also initiate procedures leading to emergency braking as required.
This millimeter-wave frequency band is not the only frequency range currently in use for automotive radar systems. A “temporary” frequency band has also been established at 24 GHz for short-term automotive electronics systems. Unfortunately, this band is already occupied by other electronic devices, including microwave radios, which add to the congestion faced by radar systems within this band (and with radar signals becoming interference for the existing microwave radio devices). The band has been deemed as “temporary” for such applications as automotive radar because it will be closed to those devices when the signal levels become too dense at 24 GHz.
This band was made available in Europe to European Union (EU) members by means of European Commission Decision 2005/50/EC. Said regulation also sets requirements for automatic deactivation devices for 24-GHz when too close to existing systems (such as radio astronomy sites), and also sets guidelines for transition to a more permanent frequency band. In Europe, the “permanent” band for automotive radar service has been allocated at 79 GHz, per European Commission Decision 2004/545/EC, which requires that this band to be made available in all EU member states.
The band from 76 to 77 GHz had been allocated to the Radio Astronomy Service (RAS) in the US, but the Federal Communications Commission (FCC) made amendments to sections of its allocations and regulations, allowing automotive radar system in that frequency band. The modifications also impacted fixed radar applications in the 76-to-77-GHz band at airport locations, using fixed radar systems to detect foreign object debris (FOD) on runways and monitor aircraft traffic as well as service vehicles on taxiways and other airport vehicle service areas that have no public access. In Europe, the European Telecommunications Standards Institute (ETSI; www.etsi.org) sets similar guidelines for radar systems at 24 and 77 GHz.
Both system and components suppliers have supported the different automotive frequency bands. TRW Automotive, for example, has developed automotive radar system solutions at 24 GHz (model AC100) for ACC and FCW applications as well as at 77 GHz (model AC3). Numerous semiconductor suppliers have enjoyed business in supplying transceiver solutions for 77-GHz automotive radar systems, including Texas Instruments with its model MRD2001 automotive radar chip set. Devices in the chip set are housed in low-loss packaging (usable through 100 GHz) which simplifies assembly for automotive manufacturers and is scalable to 4 transmit channels and 12 receive channels so that a single radar system can provide radar beams across a wide field of view for near-field, mid-field, and far-field applications.
Freescale Semiconductor has used its silicon-germanium (SiGe) BiCMOS semiconductor process as the basis for its Xtrinsic 77-GHz automotive radar semiconductor devices. And TriQuint Semiconductor supports the long- and medium-range automotive radar market with a wide portfolio of 77 GHz MMICs for front-end applications such as ACC and FCW systems. Additional semiconductor and component suppliers include Altera, Analog Devices, Fujitsu, Infineon, Millitech, NXP Semiconductors, and Skyworks Solutions.