It is a classic contrarian approach : the best way to allow a chip to communicate with another might be to remove the wires that connect them. Chips today communicate with other chips through wires that are generally welded to the chip through a process called Ball Bonding. There are several challenges with this, and the situation gets exacerbated by the kind of performance and compute density improvements happening within the chip.

Chip to Chip communication is far slower than that within a chip (primarily because the width of, and spacing between, wires within the chip are a 100 times smaller than those of wires between chips. This obviously is a performance bottleneck. Besides, an elaborate process is required to wire a chip up, making it expensive.

Proximity Communication lines up a transmitter on one chip against a receiver on another chip, with the two chips positioned very close to each other. The two form a capacitor and a voltage driven through the transmitter will result in a corresponding charge on the receiver, thus achieving communication. The method has been shown to achieve an I/O pad density 60 times greater than that possible with Ball Bonding. It thus allows larger bandwidths for a given area on the chip.

Other advantageous side-effects follow too : the conventional wire communication needs signal amplification as the external wires are larger. The power consumed and heat dissipated also increases because of the energy needed. Proximity Communication obviates the need for high amplification, resulting in smaller transmit/receive circuits, and expensive cooling. As the chips are not wired up to each other, the technique also permits chips to be easily replaced. One of the first patents in the area was awarded to Dr. Ivan Sutherland, Sun Fellow and Vice President. The idea was the overall Gold winner in The Wall Street Journal's Technology Innovation Awards in 2004.

The technology caused a stir at the Sun Labs Open House in April 2007. Dr. Hans Eberle is working on Project Sedna, a next generation datacenter switch which employs Proximity Communication.

Key to the practical deployment of proximity communication is solving the problem of rotational and translational mis-alignment : if the transmitters on one chip do not align perfectly with the receivers on the other, the coupling might not be strong enough for communication to take place. To deal with this, Greg Papadopoulos and Robert Bosnyak developed Electronic Alignment, a technique that compensates for mis-alignment by allowing transmit/receive pad positions to move correspondingly. Dr. Drost credits this technique as vital to making the technology practical.

An amusing sidelight is provided by the title of the illustration in The Register's Proximity Communication article : Chip Fornication. Considering that the chips are not in contact with each other, El Reg must have meant Coupling 2.0.

Tags : Proximity Communication Chip Interconnect