New high frequency amplifier harnesses millimeter waves in silicon for fast wireless

February 11, 2009

New imaging and high capacity wireless communications systems are one step closer to reality, thanks to a millimeter wave amplifier invented at the University of California, San Diego and unveiled on Feb 11, 2009 at the prestigious International Solid-State Circuits Conference (ISSCC) in San Francisco, Calif.

The new silicon-based amplifier marks progress toward high capacity wireless communications systems that will operate at millimeter wave frequencies (70-110GHz) and could provide data transfer rates as fast as 10 Gigabits per second over a kilometer. Toward this goal, the new amplifier provides both high gain (the ability to increase the volume of a signal) and high bandwidth (the ability to do it over a broad range of tones). It has a direct transmission line path from the input to the output that carries electromagnetic waves--undisrupted--across the surface of a silicon chip. Amplification "stages" along this transmission line boost the signal power by monitoring the signal amplitude and generating feedback in just trillionths of a second, feedback that injects additional energy in phase to the signal. The amplifier provides record-breaking gain of 26-30dB at 100GHz and allows wave propagation along the chip surface.

James Buckwalter, an assistant professor in the Department of Electrical and Computer Engineering at UC San Diego's Jacobs School of Engineering, invented the amplifier and named it the Cascaded Constructive Wave Amplifier.

"Cascaded constructive wave amplification is a new circuit architecture that can push silicon into new operating regimes near the fundamental limits of Moore's Law and allow the ultra high data rates that the millimeter wavelength range of the electromagnetic spectrum offers," explained Buckwalter.

The millimeter wavelength range of the electromagnetic spectrum is relatively unexplored for commercial use, in part, because it has been difficult and expensive to build the necessary high frequency amplifiers. Many of today's millimeter wave amplifiers, for example, require exotic and expensive semiconductor materials.

"We're exploring how silicon can play a role at frequencies exceeding 100 Gigahertz. Silicon has the advantage of allowing inexpensive integration of microwave and now perhaps millimeter wave components," said Buckwalter.

A is for Amplification

Today's Wi-Fi and WiMax systems operate at a frequency of 2.5-5GHz and are capable of handling megabits of information per second. "If you want higher data rates, you need to find ways to transmit information wirelessly at rates faster than what is available at 2.5 Gigahertz. This new amplifier is aimed at opening millimeter wave frequency bands, where much more bandwidth are available and where higher data transfer rates, as fast as 10 Gigabits per second over a kilometer, are possible," explained Buckwalter.

Point-to-point wireless communication is a low-cost approach to getting optical fiber speeds. "You could use this amplification method to boost signal strength of a 100 Gigahertz signal from the transmitter in your ISP and also at the receiver in your home to detect the signal," explained Buckwalter.

Feedback Tames the Wave

"The really cool thing about this chip is that it's the first time traveling waves have been amplified along an uninterrupted transmission line...we've found a new architecture that allows higher gain than what people supposed for waves traveling near the speed of light on silicon chips," said Buckwalter.

The periodic amplification stages along the transmission line are crucial to the amplification process. They monitor waves as they propagate through the transmission line and spontaneously inject energy into the wave without interrupting its propagation down the transmission line.

In particular, the strength of the wave is constantly monitored at the output side of each amplification stage. Feedback is provided through a fast transistor that feeds energy into the input of the transmission line and hits the wave with that energy 2.5 trillionths of a second later--a quarter of the wave's period. In this way, the wave is constantly being strengthened as it moves uninhibited through each of the amplification stages along the transmission line.

This new amplifier design is distinctly different from existing amplifier technologies. The new Cascaded Constructive Wave Amplifier provides high gain--the signal gain increases exponentially with the number of amplification stages--without absorbing and regenerating the wave energy. The cascaded amplifiers that are found in all cell phones also have high gain----but they absorb and regenerate signals.

"We've taken a wave that travels along the surface of the silicon near the speed of light and found a way to amplify the signal strength without interrupting the wave," said Buckwalter. "We have found a way to tame millimeter waves on silicon."
-end-
ISSCC 2009 Paper citation: "A 26dB Gain, 100GHz Si/SiGe Cascaded Constructive Wave Amplifier," by James Buckwalter and Joohwa Kim from the Department of Electrical and Computer Engineering from the UC San Diego Jacobs School of Engineering. A copy of the paper is available upon request.

This work was supported through a DARPA Young Faculty Award to James Buckwalter.

University of California - San Diego

Related Silicon Articles from Brightsurf:

Single photons from a silicon chip
Quantum technology holds great promise: Quantum computers are expected to revolutionize database searches, AI systems, and computational simulations.

For solar boom, scrap silicon for this promising mineral
Cornell University engineers have found that photovoltaic wafers in solar panels with all-perovskite structures outperform photovoltaic cells made from state-of-the-art crystalline silicon, as well as perovskite-silicon tandem cells, which are stacked pancake-style cells that absorb light better.

Surprisingly strong and deformable silicon
Researchers at ETH have shown that tiny objects can be made from silicon that are much more deformable and stronger than previously thought.

A leap in using silicon for battery anodes
Scientists have come up with a novel way to use silicon as an energy storage ingredient.

Flexible thinking on silicon solar cells
Combining silicon with a highly elastic polymer backing produces solar cells that have record-breaking stretchability and high efficiency.

No storm in a teacup -- it's a cyclone on a silicon chip
University of Queensland researchers have combined quantum liquids and silicon-chip technology to study turbulence for the first time, opening the door to new navigation technologies and improved understanding of the turbulent dynamics of cyclones and other extreme weather.

Black silicon can help detect explosives
Scientists from Far Eastern Federal University (FEFU), Far Eastern Branch of the Russian Academy of Sciences, Swinburne University of Technology, and Melbourne Center for Nanofabrication developed an ultrasensitive detector based on black silicon.

2D antimony holds promise for post-silicon electronics
Researchers in the Cockrell School of Engineering are searching for alternative materials to silicon with semiconducting properties that could form the basis for an alternative chip.

Silicon technology boost with graphene and 2D materials
In a review published in Nature, ICFO researchers and collaborators report on the current state, challenges, opportunities of graphene and 2D material integration in Silicon technology.

Light and sound in silicon chips: The slower the better
Acoustics is a missing dimension in silicon chips because acoustics can complete specific tasks that are difficult to do with electronics and optics alone.

Read More: Silicon News and Silicon Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.