KU Leuven and Nokia Bell Labs give copper speed of light

Researchers of KU Leuven and Nokia Bell Labs have realised a chip that can send 20 Gbps over a standard coax cable. This way they demonstrate that not all network cables have to be replaced by optical fiber.

by MICAS (KU Leuven)

Thanks to its much higher bandwidth, optical fiber is replacing copper cables in high speed data networks. But copper is fighting back. Especially for the connection between our homes and the network in the street, the good old telephone and coax cables keep on performing. To give this “curb to customer” connection a speed comparable to optical fiber, Nokia Bell Labs in Antwerp is collaborating with MICAS, the division of the KU Leuven specialised in chip design. The KU Leuven is part of Nokia Bell Labs’ Distinguished Academic Partners Program, a cooperation between Bell Labs researchers and researchers from the world’s top universities and academic organisations to deliver the innovations needed to transform human existence.

Standard CMOS process

After the acquisition of Alcatel-Lucent by Nokia, the research department in Antwerp kept its name Bell Labs, forming Nokia Bell Labs. “Den Bell”, as the company is still called in the region, played a crucial role in the development of digital network infrastructure using traditional telephone wires (ADSL, VDSL and its successors). Today this domain is still one of the core activities. Researchers of Nokia Bell Labs have turned to KU Leuven to develop the next generation of hardware for communication over existing copper networks. The collaboration has resulted in a chip that can send data over a coax cable at a speed of 20 Gbps. This way the connection between the home and the street does not have to be replaced by optical fiber, which means a huge cost saving.

Thanks to the standard CMOS process, the new chip can be combined with the other electronic circuitry necessary to send and receive the bits and bytes.

The innovation is not only what the chip can do, it’s also how it’s made. Current chips to drive copper lines are made in a specific technology, which is expensive, power hungry and difficult to integrate in the complete communication system. The researchers from KU Leuven and Nokia Bell Labs used a standard CMOS process for their new chip. This is the production process which is also used for DSP chips and microprocessors. This way their chip can be combined with the other electronic circuitry necessary to send and receive the bits and bytes in a reliable way. The result: a compact, cost efficient and energy saving all-in-one solution.

Stack of 16 transistors

The challenge is to match the apparently incompatible needs of the application with the possibilities of the technology. The circuits should be able to put 10V on the cable, while the transistors in a CMOS process operate at around 1V. The researchers of MICAS came up with a smart solution. They stacked several transistors on top of each other. Each transistor works at its nominal voltage of 1V, but together they can deliver a much higher voltage. In this case the researchers stacked 16 transistors. Thanks to their expertise in the design of analog integrated circuits the MICAS researchers managed to find a suitable working point for all of these transistors, while also keeping the circuit as a whole within the voltage boundary conditions.

Doubling speed

The team validated the chip designs by realising them in an advanced standard CMOS technology. They made a prototype system that was extensively put to the test. The speed at which the system spits out the bits onto the copper network hit the 20 Gbps mark. This is a doubling compared to the state-of-the-art.

The speed at which the system spits out the bits onto the copper network is a doubling compared to the state-of-the-art.

The prototype will form the basis for future network equipment that connects our houses to the ultra-fast optical fiber network. There will be no bottleneck at our doorstep, and this without having to replace the existing copper cables! No digging, no fibers and no expensive optical hardware needed in and around the house.

Nokia Bell Labs will continue its collaboration with MICAS. Together, they will further improve the current prototype. They will also start to apply aspects of machine learning to increase the efficiency of the signal processing.

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The research leading to this breakthrough result was partly funded through the IWT/VLAIO project DAX.